user471: According to this answer:

Nirvana is the ground layer ("dhatu") underneath them all. ...
Nirvana is this most fundamental law (the formula, the rule, the
  program) according to which the Universe develops.

This comment also seems to support that idea:

... the expression "the unmade is a foundation for phenomena" is
  probably an agreeable thing to say given than it occurs in the pali
  discourses "amatogadha" meaning deathless as foundation or deathless
  as ground. There is also a reasonable way to defend it, which makes it
  not a real point of controversy imo but a rather reasonable assumption
  in that the pali wording is to be taken at facevalue and read
  literally.

This sounds very similar to Advaita which describes Brahman as the substratum or foundation of all phenomena, just as different kinds of pots and plates made of clay, all have clay as their foundation.
Questions:

Does the notion "Nirvana is the ground layer" come from Mahayana? From which Mahayana subschool or text?
Does the Pali Canon support the notion that "Nirvana is the ground layer"? Does this relate to "amatogadha" some how? What's that?
The ground layer concept sounds similar to luminous mind. However, we know that Nirvana is unconditioned, while the luminous mind is conditioned. Does this "Nirvana is the ground layer" concept connect to the luminous mind in any way?


user8157: It seems Nibbana is described below; which does not sound like ground layer underneath:

“Suppose, bhikkhus, there was a house or a hall with a peaked roof,
  with windows on the northern, southern, and eastern sides. When the
  sun rises and a beam of light enters through a window, where would it
  become established?”
“On the western wall, venerable sir.”
“If there were no western wall, where would it become established?”
“On the earth, venerable sir.”
“If there were no earth, where would it become established?”
“On the water, venerable sir.”
“If there were no water, where would it become established?”
“It would not become established anywhere, venerable sir.”
“So too, bhikkhus, if there is no lust for the nutriment edible food …
  for the nutriment contact … for the nutriment mental volition … for
  the nutriment consciousness … consciousness does not become
  established there and come to growth. Where consciousness does not
  become established and come to growth … … I say that is without
  sorrow, anguish, and despair.”
SN 12.64


user-1: I have never seen this discussed before but it is something i've been interested in as far as expression and meaning goes. There are several meanings which can be arrived at;
 1. There is ultimate mind of all beings, we are all one.
 2. There is a state of mind which is impetruble, immovable, unaffected, such that is the ultimate goal ultimate security.
 3. There is that which is mind and that is mind-made. With the cessation of mind which is mind made there is discernment of not mind, whereas that which can be taken to be a mind of a being would be extinct and not in play. 
The #3 is the one that can be further is explained that mind of a being exists in as far as the aggregates exist, if there are no aggregates, in a context where they are not in play "have no footing" there can be no talk about the world let alone a person or a person soul. 
If there is with the cessation of the mind made a discernment of a discernable reality which isn't included in the aggregates then the question can not be posed; 'Isn't this discernment then a consciousness of some sort?' 

The answer would be that consciosness per definition is associated with contact and three types of fabrication. With the cessation of mind-made phenomena, the context presumes that it isn't consciousness but a discernment of it's cessation that is being talked about. 
That which is discerned is cognized! 
What is cognized there is the cessation, extinguishment; Nibbana, resolution of all fabrication..

Thus the perspective of the observer or the one who experiences is contained to context where existence of the aggregates is affirmed for this or that person who sees for that is in as far as his existence is affirmed.
Nibbana as ground quite interesting because the curious thing is why are the Dhamma amatogadha if, how and when vinnanam anidassanam is also taken to have the unconditioned as it's referent. 
Which is of course extremely interesting because in the context of vinnanam anidassanam the elements are said not to be said to be ceased but are as not gaining footing, which also can be taken to be a way to navigate the context between existence of aggregates being in and out of play, affirmed or not-affirmed.
That is the gist of it, further i think there is a good explaination because the paraphrasing of Kevatta's question reflects very well the need to contain the narrative of a person and associated aggregates and their cessation and arising to one side and that which is discerned as highest pleasure as another. 
The fact is that the notion of an Arahants discernment exists only in as far as his life force faculty persists, when it is extinguished the discernment faculty ceases. So if ie Arahant's last perception is that of extinguishment, then even that is ceased with his death because dead people don't meditate. 
As for this controversy there is the AN10.58 which literally says that sabbe dhamme amatogadha. Thanissaro translates it as footing and so does Piya Tan. Sujato and Bodhi translate it as 'culminating'. Sujato acknowledges that the literal translation is like Thanissaro pins it but according to his own conjecture he thinks it is an idiom and should not be translated as is expressed.
Bodhi is also inconsistent because he translates one place that discernment does gain a footing in the deathless but not all phenomena do that basically. It is inconsistent.
Sujato considers the matter solved as far as i know and nobody really discusses this.
I've written some posts on this if you are interested.

user16296: Yeah, many Mahayana texts seem to imply Advaitin Brahman with Buddha-dhatu, Buddha-nature, tathagatgarbha etc. I encounter a lot of such terminologies while reading texts of supposedly 2nd or 3rd turning wheels. In section 1, chapter 3  of Mahayana Parinirvana Sutta - 

“Even though he has said that all phenomena [dharmas] are devoid of the Self, it is not that they are completely/ truly devoid of the Self. What is this Self? Any phenomenon [dharma] that is true [satya], real [tattva], eternal [nitya], sovereign/ autonomous/ self-governing [aisvarya], and whose ground/ foundation is unchanging [asraya-aviparinama], is termed 'the Self' [atman]. This is as in the case of the great Doctor who well understands the milk medicine. The same is the case with the Tathagata. For the sake of beings, he says ’there is the Self in all things’. O you the four classes! Learn Dharma thus!" [Emphasis added].

Devoid of any interpretation, In this text Buddha talking about the self as a sentient self-aware entity common ground of all which is the same as Brahman of Advaitins. It is not ego-substance or anything that can belong to any individual like Atma of dualists. He himself clarified what he meant by Self in the same chapter as follows - 

...Common mortals and the ignorant may measure the size of their own self and say, 'It is like the size of a thumb, like a mustard seed, or like the size of a mote.' When the Tathagata speaks of Self, in no case are things thus. That is why he says: 'All things have no Self...

Also, Bodhidharma in his The Treatise on the Two Entrances and Four Practices says - 

Many roads lead to the Path, but basically, there are only
  two: reason and practice. To enter by reason means to realize the
  essence through instruction and to realize that all living things
  share the same true nature, which isn't apparent because it's
  shrouded by sensation and delusion. Those who turn from delusion
  back to reality, who meditate on walls, the absence of self and
  other, the oneness of mortal and sage, and who remain unmoved
  even by scriptures are in complete and unspoken agreement with
  reason. Without moving, without effort, they enter, we say, by
  reason. - Page 3, Zen teachings of Bodhidharma


user43: 1. Does the notion "Nirvana is the ground layer" come from Mahayana? From which Mahayana subschool or text?
Yes. Well, they don't call it "Nirvana" - because they think this word got spoiled by abuse and acquired a dualistic meaning (as the opposite of Samsara). Instead, they simply call it "The Ground of All", "The Absolute", "The Unity of Relative and Absolute" etc.
This is certainly a well-known feature of Tibetan Buddhist lineages in Karma Kagyu and Nyungma schools that adhere to the so-called Shentong interpretation of Emptiness: 

https://en.wikipedia.org/wiki/Ground_(Dzogchen)
https://en.wikipedia.org/wiki/Rangtong-Shentong


Shentong was systematized and articulated under that name by Dolpopa Sherab Gyaltsen (1292–1361), who identified absolute reality with the Buddha-nature.

...  

The earliest shentong views are usually asserted to have been presented in a group of treatises variously attributed jointly to Asanga and Maitreyanātha, especially in the treatise known as the Unsurpassed Continuum (Uttaratantraśāstra, also called the Ratnagotravibhāga),[22] and in a body of Mādhyamaka treatises attributed to Nāgārjuna (e.g., the Dharmadhātustava, "In praise of the Dharmadhatu").

...  

Rigpa has two aspects, namely kadag and lhun grub. Kadag means "purity" or specifically "primordial purity". Lhun grub in Tibetan normally implies automatic, self-caused or spontaneous actions or processes. As quality of rigpa it means "spontaneous presence". It may also mean "having a self-contained origin", being primordially Existent, without an origin, self-existent.

...  

Buddha-nature is immaculate. It is profound, serene, unfabricated suchness, an uncompounded expanse of luminosity; nonarising, unceasing, primordial peace, spontaneously present nirvana.

...  

The practical training of the Dzogchen path is traditionally, and most simply, described [as:] To see directly the Absolute state, the Ground of our being is the View; the way of stabilising that view, and making it an unbroken experience is Meditation; and integrating the View into our entire reality, and life, is what is meant by Action.

In Chan and Zen schools this is generally discussed under the heading of Buddha Nature and "One's True Nature":

https://en.wikipedia.org/wiki/Buddha-nature


... the ultimate universal ground also has always been with the Buddha-Essence (Tathagatagarbha), and this essence in terms of the universal ground has been taught by the Tathagata. The fools who do not know it, because of their habits, see even the universal ground as (having) various happiness and suffering and actions and emotional defilements. Its nature is pure and immaculate, its qualities are as wishing-jewels; there are neither changes nor cessations. Whoever realizes it attains Liberation

...  

This "dharma of the one mind", which is the "original tathagatagarbha", is said to be "calm and motionless" [...] The tathagatagarbha is equated with the "original edge of reality" (bhutakoti) that is beyond all distinctions - the equivalent of original enlightenment, or the essence.

2. Does the Pali Canon support the notion that "Nirvana is the ground layer"? Does this relate to "amatogadha" some how? What's that?
I believe it does. There are many pointers spread around Dependent Origination teachings, and all the descriptions of Nibbana, with references like amatogadha and amata-dhatu, the Buddha's story about him getting "to the end of the world" etc.
3. The ground layer concept sounds similar to luminous mind. However, we know that Nirvana is unconditioned, while the luminous mind is conditioned. Does this "Nirvana is the ground layer" concept connect to the luminous mind in any way?
I don't know why you say "we know" that luminous mind is conditioned. In Mahayana, the fundamental luminosity of mind is considered unconditioned (see Rigpa, Clear Light). 

https://en.wikipedia.org/wiki/Rigpa
https://en.wikipedia.org/wiki/Luminous_mind#Vajrayana


In Tibetan Buddhist Dzogchen literature, luminosity ('od gsal) is associated with an aspect of the Ground termed "spontaneous presence" (Lhun grub), meaning a presence that is uncreated and not based on anything causally extraneous to itself. This term is often paired with 'original-purity' (ka dag), which is associated with emptiness (shunyata), and are both seen as inseparable aspects of the Ground.


471: <p>According to <a href="https://buddhism.stackexchange.com/a/34630/471">this answer</a>:</p>

<blockquote>
  <p>Nirvana is the ground layer ("dhatu") underneath them all. ...</p>
  
  <p>Nirvana is this most fundamental law (the formula, the rule, the
  program) according to which the Universe develops.</p>
</blockquote>

<p><a href="https://buddhism.stackexchange.com/q/34616/471#comment58414_34619">This comment</a> also seems to support that idea:</p>

<blockquote>
  <p>... the expression "the unmade is a foundation for phenomena" is
  probably an agreeable thing to say given than it occurs in the pali
  discourses "amatogadha" meaning deathless as foundation or deathless
  as ground. There is also a reasonable way to defend it, which makes it
  not a real point of controversy imo but a rather reasonable assumption
  in that the pali wording is to be taken at facevalue and read
  literally.</p>
</blockquote>

<p>This sounds very similar to Advaita which describes Brahman as the substratum or foundation of all phenomena, just as different kinds of pots and plates made of clay, all have clay as their foundation.</p>

<p>Questions:</p>

<ol>
<li>Does the notion "Nirvana is the ground layer" come from Mahayana? From which Mahayana subschool or text?</li>
<li>Does the Pali Canon support the notion that "Nirvana is the ground layer"? Does this relate to "amatogadha" some how? What's that?</li>
<li>The ground layer concept sounds similar to <a href="https://buddhism.stackexchange.com/q/25210/471">luminous mind</a>. However, we know that Nirvana is unconditioned, while the luminous mind is conditioned. Does this "Nirvana is the ground layer" concept connect to the luminous mind in any way?</li>
</ol>
 8157: <p>It seems Nibbana is described below; which does not sound like ground layer underneath:</p>

<blockquote>
  <p>“Suppose, bhikkhus, there was a house or a hall with a peaked roof,
  with windows on the northern, southern, and eastern sides. When the
  sun rises and a beam of light enters through a window, where would it
  become established?”</p>
  
  <p>“On the western wall, venerable sir.”</p>
  
  <p>“If there were no western wall, where would it become established?”</p>
  
  <p>“On the earth, venerable sir.”</p>
  
  <p>“If there were no earth, where would it become established?”</p>
  
  <p>“On the water, venerable sir.”</p>
  
  <p>“If there were no water, where would it become established?”</p>
  
  <p>“It would not become established anywhere, venerable sir.”</p>
  
  <p>“So too, bhikkhus, if there is no lust for the nutriment edible food …
  for the nutriment contact … for the nutriment mental volition … for
  the nutriment consciousness … consciousness does not become
  established there and come to growth. Where consciousness does not
  become established and come to growth … … I say that is without
  sorrow, anguish, and despair.”</p>
  
  <p><a href="https://suttacentral.net/sn12.64/en/bodhi" rel="nofollow noreferrer">SN 12.64</a></p>
</blockquote>
 -1: <p>I have never seen this discussed before but it is something i've been interested in as far as expression and meaning goes. There are several meanings which can be arrived at;
 1. There is ultimate mind of all beings, we are all one.
 2. There is a state of mind which is impetruble, immovable, unaffected, such that is the ultimate goal ultimate security.
 3. There is that which is mind and that is mind-made. With the cessation of mind which is mind made there is discernment of not mind, whereas that which can be taken to be a mind of a being would be extinct and not in play. </p>

<p>The #3 is the one that can be further is explained that mind of a being exists in as far as the aggregates exist, if there are no aggregates, in a context where they are not in play "have no footing" there can be no talk about the world let alone a person or a person soul. </p>

<p>If there is with the cessation of the mind made a discernment of a discernable reality which isn't included in the aggregates then the question can not be posed; 'Isn't this discernment then a consciousness of some sort?' </p>

<ul>
<li>The answer would be that consciosness per definition is associated with contact and three types of fabrication. With the cessation of mind-made phenomena, the context presumes that it isn't consciousness but a discernment of it's cessation that is being talked about. </li>
<li>That which is discerned is cognized! </li>
<li>What is cognized there is the cessation, extinguishment; Nibbana, resolution of all fabrication..</li>
</ul>

<p>Thus the perspective of the observer or the one who experiences is contained to context where existence of the aggregates is affirmed for this or that person who sees for that is in as far as his existence is affirmed.</p>

<p>Nibbana as ground quite interesting because the curious thing is why are the Dhamma amatogadha if, how and when vinnanam anidassanam is also taken to have the unconditioned as it's referent. </p>

<p>Which is of course extremely interesting because in the context of vinnanam anidassanam the elements are said not to be said to be ceased but are as not gaining footing, which also can be taken to be a way to navigate the context between existence of aggregates being in and out of play, affirmed or not-affirmed.</p>

<p>That is the gist of it, further i think there is a good explaination because the paraphrasing of Kevatta's question reflects very well the need to contain the narrative of a person and associated aggregates and their cessation and arising to one side and that which is discerned as highest pleasure as another. </p>

<p>The fact is that the notion of an Arahants discernment exists only in as far as his life force faculty persists, when it is extinguished the discernment faculty ceases. So if ie Arahant's last perception is that of extinguishment, then even that is ceased with his death because dead people don't meditate. </p>

<p>As for this controversy there is the AN10.58 which literally says that sabbe dhamme amatogadha. Thanissaro translates it as footing and so does Piya Tan. Sujato and Bodhi translate it as 'culminating'. Sujato acknowledges that the literal translation is like Thanissaro pins it but according to his own conjecture he thinks it is an idiom and should not be translated as is expressed.</p>

<p>Bodhi is also inconsistent because he translates one place that discernment does gain a footing in the deathless but not all phenomena do that basically. It is inconsistent.</p>

<p>Sujato considers the matter solved as far as i know and nobody really discusses this.</p>

<p>I've written some posts on this if you are interested.</p>
 16296: <p>Yeah, many Mahayana texts seem to imply Advaitin Brahman with Buddha-dhatu, Buddha-nature, tathagatgarbha etc. I encounter a lot of such terminologies while reading texts of supposedly 2nd or 3rd turning wheels. In section 1, chapter 3  of <a href="https://www.wisdomlib.org/buddhism/book/the-mahayana-mahaparinirvana-sutra/d/doc59402.html" rel="nofollow noreferrer">Mahayana Parinirvana Sutta</a> - </p>

<blockquote>
  <p>“Even though he has said that all phenomena [dharmas] are devoid of the Self, it is not that they are completely/ truly devoid of the Self. What is this Self? Any phenomenon [dharma] that is true [satya], real [tattva], eternal [nitya], sovereign/ autonomous/ self-governing [aisvarya], and <strong>whose ground/ foundation is unchanging</strong> [asraya-aviparinama], is termed 'the Self' [atman]. This is as in the case of the great Doctor who well understands the milk medicine. The same is the case with the Tathagata. For the sake of beings, he says ’there is the Self in all things’. O you the four classes! Learn Dharma thus!" [Emphasis added].</p>
</blockquote>

<p>Devoid of any interpretation, In this text Buddha talking about the self as a sentient self-aware entity common ground of all which is the same as Brahman of Advaitins. It is not ego-substance or anything that can belong to any individual like Atma of dualists. He himself clarified what he meant by Self in the same chapter as follows - </p>

<blockquote>
  <p>...Common mortals and the ignorant may measure the size of their own self and say, 'It is like the size of a thumb, like a mustard seed, or like the size of a mote.' <strong>When the Tathagata speaks of Self, in no case are things thus. That is why he says: 'All things have no Self</strong>...</p>
</blockquote>

<p>Also, Bodhidharma in his The Treatise on the Two Entrances and Four Practices says - </p>

<blockquote>
  <p>Many roads lead to the Path, but basically, there are only
  two: reason and practice. To enter by reason means to realize the
  essence through instruction and <strong>to realize that all living things
  share the same true nature, which isn't apparent because it's
  shrouded by sensation and delusion.</strong> Those who turn from delusion
  back to reality, who meditate on walls, the absence of self and
  other, the oneness of mortal and sage, and who remain unmoved
  even by scriptures are in complete and unspoken agreement with
  reason. Without moving, without effort, they enter, we say, by
  reason. - Page 3, Zen teachings of Bodhidharma</p>
</blockquote>
 43: <h2>1. Does the notion "Nirvana is the ground layer" come from Mahayana? From which Mahayana subschool or text?</h2>

<p>Yes. Well, they don't call it "Nirvana" - because they think this word got spoiled by abuse and acquired a dualistic meaning (as the opposite of Samsara). Instead, they simply call it "The Ground of All", "The Absolute", "The Unity of Relative and Absolute" etc.</p>

<p>This is certainly a well-known feature of Tibetan Buddhist lineages in Karma Kagyu and Nyungma schools that adhere to the so-called Shentong interpretation of Emptiness: </p>

<ul>
<li><a href="https://en.wikipedia.org/wiki/Ground_(Dzogchen)" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/Ground_(Dzogchen)</a></li>
<li><a href="https://en.wikipedia.org/wiki/Rangtong-Shentong" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/Rangtong-Shentong</a></li>
</ul>

<blockquote>
  <p>Shentong was systematized and articulated under that name by Dolpopa Sherab Gyaltsen (1292–1361), who identified absolute reality with the Buddha-nature.</p>
</blockquote>

<p>...  </p>

<blockquote>
  <p>The earliest shentong views are usually asserted to have been presented in a group of treatises variously attributed jointly to Asanga and Maitreyanātha, especially in the treatise known as the Unsurpassed Continuum (Uttaratantraśāstra, also called the Ratnagotravibhāga),[22] and in a body of Mādhyamaka treatises attributed to Nāgārjuna (e.g., the Dharmadhātustava, "In praise of the Dharmadhatu").</p>
</blockquote>

<p>...  </p>

<blockquote>
  <p>Rigpa has two aspects, namely kadag and lhun grub. Kadag means "purity" or specifically "primordial purity". Lhun grub in Tibetan normally implies automatic, self-caused or spontaneous actions or processes. As quality of rigpa it means "spontaneous presence". It may also mean "having a self-contained origin", being primordially Existent, without an origin, self-existent.</p>
</blockquote>

<p>...  </p>

<blockquote>
  <p>Buddha-nature is immaculate. It is profound, serene, unfabricated suchness, an uncompounded expanse of luminosity; nonarising, unceasing, primordial peace, spontaneously present nirvana.</p>
</blockquote>

<p>...  </p>

<blockquote>
  <p>The practical training of the Dzogchen path is traditionally, and most simply, described [as:] To see directly the Absolute state, the Ground of our being is the View; the way of stabilising that view, and making it an unbroken experience is Meditation; and integrating the View into our entire reality, and life, is what is meant by Action.</p>
</blockquote>

<p>In Chan and Zen schools this is generally discussed under the heading of Buddha Nature and "One's True Nature":</p>

<ul>
<li><a href="https://en.wikipedia.org/wiki/Buddha-nature" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/Buddha-nature</a></li>
</ul>

<blockquote>
  <p>... the ultimate universal ground also has always been with the Buddha-Essence (Tathagatagarbha), and this essence in terms of the universal ground has been taught by the Tathagata. The fools who do not know it, because of their habits, see even the universal ground as (having) various happiness and suffering and actions and emotional defilements. Its nature is pure and immaculate, its qualities are as wishing-jewels; there are neither changes nor cessations. Whoever realizes it attains Liberation</p>
</blockquote>

<p>...  </p>

<blockquote>
  <p>This "dharma of the one mind", which is the "original tathagatagarbha", is said to be "calm and motionless" [...] The tathagatagarbha is equated with the "original edge of reality" (bhutakoti) that is beyond all distinctions - the equivalent of original enlightenment, or the essence.</p>
</blockquote>

<h2>2. Does the Pali Canon support the notion that "Nirvana is the ground layer"? Does this relate to "amatogadha" some how? What's that?</h2>

<p>I believe it does. There are many pointers spread around Dependent Origination teachings, and all the descriptions of Nibbana, with references like <em>amatogadha</em> and <em>amata-dhatu</em>, the Buddha's story about him getting "to the end of the world" etc.</p>

<h2>3. The ground layer concept sounds similar to luminous mind. However, we know that Nirvana is unconditioned, while the luminous mind is conditioned. Does this "Nirvana is the ground layer" concept connect to the luminous mind in any way?</h2>

<p>I don't know why you say "we know" that luminous mind is conditioned. In Mahayana, the fundamental luminosity of mind is considered unconditioned (see Rigpa, Clear Light). </p>

<ul>
<li><a href="https://en.wikipedia.org/wiki/Rigpa" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/Rigpa</a></li>
<li><a href="https://en.wikipedia.org/wiki/Luminous_mind#Vajrayana" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/Luminous_mind#Vajrayana</a></li>
</ul>

<blockquote>
  <p>In Tibetan Buddhist Dzogchen literature, luminosity ('od gsal) is associated with an aspect of the Ground termed "spontaneous presence" (Lhun grub), meaning a presence that is uncreated and not based on anything causally extraneous to itself. This term is often paired with 'original-purity' (ka dag), which is associated with emptiness (shunyata), and are both seen as inseparable aspects of the Ground.</p>
</blockquote>
