All of lore.kernel.org
 help / color / mirror / Atom feed
From: Christoph Hellwig <hch@lst.de>
To: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Maxim Kochetkov <fido_max@inbox.ru>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	robh@kernel.org, mpe@ellerman.id.au, aou@eecs.berkeley.edu,
	palmer@dabbelt.com, paul.walmsley@sifive.com,
	Conor Dooley <conor@kernel.org>,
	hch@lst.de
Subject: Re: [PATCH 1/1] riscv: set ARCH_DMA_DEFAULT_COHERENT if RISCV_DMA_NONCOHERENT is not set
Date: Fri, 22 Dec 2023 05:14:28 +0100	[thread overview]
Message-ID: <20231222041428.GA2803@lst.de> (raw)
In-Reply-To: <f31d929c-fa0a-4046-be05-38e92afa5d92@flygoat.com>

On Thu, Dec 21, 2023 at 10:27:33PM +0000, Jiaxun Yang wrote:
>
>
> 在 2023/12/21 20:29, Conor Dooley 写道:
>> + Christoph
>>
>> I don't think this patch is correct. Regardless of whether we support
>> cache management operations, DMA is assumed to be coherent unless
>> peripherals etc are specified to otherwise in DT (or however ACPI deals
>> with that kind of thing).
>>
>> What problem are you trying to solve here?
>>
>> On Thu, Dec 21, 2023 at 09:51:52PM +0300, Maxim Kochetkov wrote:
>>> Not all the RISCV are DMA coherent by default.
>
> Sorry for chime in here.
> IMO if your platform is not coherent by default, just insert 
> "dma-noncoherent"
> at devicetree root node.

Exactly.  ARCH_DMA_DEFAULT_COHERENTis a setting that just says for
a given architecture assumes coherent unless otherwise specified,
which has historically been the case for mips.  Not setting it means
non-coherent unless specified, which has historially been the case
for arm.

RISC-V starte out without support for non-coherent DMA, and high ups
in RISCV still told me in 2019 that RISC-V doesn't need cache
management instructions because no new hardware would ever not be
dma coherent.  Yeah, right..

Anyay, Linux for RISC-V has historically been coherent only and then
coherent default, so this option is wrong, and you need to mark
you platform as non-coherent by inserting dma-noncoherent somewhere.


_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@lst.de>
To: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Maxim Kochetkov <fido_max@inbox.ru>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	robh@kernel.org, mpe@ellerman.id.au, aou@eecs.berkeley.edu,
	palmer@dabbelt.com, paul.walmsley@sifive.com,
	Conor Dooley <conor@kernel.org>,
	hch@lst.de
Subject: Re: [PATCH 1/1] riscv: set ARCH_DMA_DEFAULT_COHERENT if RISCV_DMA_NONCOHERENT is not set
Date: Fri, 22 Dec 2023 05:14:28 +0100	[thread overview]
Message-ID: <20231222041428.GA2803@lst.de> (raw)
In-Reply-To: <f31d929c-fa0a-4046-be05-38e92afa5d92@flygoat.com>

On Thu, Dec 21, 2023 at 10:27:33PM +0000, Jiaxun Yang wrote:
>
>
> 在 2023/12/21 20:29, Conor Dooley 写道:
>> + Christoph
>>
>> I don't think this patch is correct. Regardless of whether we support
>> cache management operations, DMA is assumed to be coherent unless
>> peripherals etc are specified to otherwise in DT (or however ACPI deals
>> with that kind of thing).
>>
>> What problem are you trying to solve here?
>>
>> On Thu, Dec 21, 2023 at 09:51:52PM +0300, Maxim Kochetkov wrote:
>>> Not all the RISCV are DMA coherent by default.
>
> Sorry for chime in here.
> IMO if your platform is not coherent by default, just insert 
> "dma-noncoherent"
> at devicetree root node.

Exactly.  ARCH_DMA_DEFAULT_COHERENTis a setting that just says for
a given architecture assumes coherent unless otherwise specified,
which has historically been the case for mips.  Not setting it means
non-coherent unless specified, which has historially been the case
for arm.

RISC-V starte out without support for non-coherent DMA, and high ups
in RISCV still told me in 2019 that RISC-V doesn't need cache
management instructions because no new hardware would ever not be
dma coherent.  Yeah, right..

Anyay, Linux for RISC-V has historically been coherent only and then
coherent default, so this option is wrong, and you need to mark
you platform as non-coherent by inserting dma-noncoherent somewhere.


  reply	other threads:[~2023-12-22  4:14 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-12-21 18:51 [PATCH 1/1] riscv: set ARCH_DMA_DEFAULT_COHERENT if RISCV_DMA_NONCOHERENT is not set Maxim Kochetkov
2023-12-21 18:51 ` Maxim Kochetkov
2023-12-21 20:29 ` Conor Dooley
2023-12-21 20:29   ` Conor Dooley
2023-12-21 22:27   ` Jiaxun Yang
2023-12-21 22:27     ` Jiaxun Yang
2023-12-22  4:14     ` Christoph Hellwig [this message]
2023-12-22  4:14       ` Christoph Hellwig
2023-12-22 14:39       ` Maxim Kochetkov
2023-12-22 14:39         ` Maxim Kochetkov
2023-12-22 14:54         ` Conor Dooley
2023-12-22 14:54           ` Conor Dooley
2023-12-22 15:04           ` Christoph Hellwig
2023-12-22 15:04             ` Christoph Hellwig
2023-12-22 15:38           ` Maxim Kochetkov
2023-12-22 15:38             ` Maxim Kochetkov
2023-12-22 15:45             ` Jiaxun Yang
2023-12-22 15:45               ` Jiaxun Yang
2023-12-22 15:53               ` Maxim Kochetkov
2023-12-22 15:53                 ` Maxim Kochetkov
2023-12-22 16:01                 ` Jiaxun Yang
2023-12-22 16:01                   ` Jiaxun Yang
2023-12-23  4:59                   ` Christoph Hellwig
2023-12-23  4:59                     ` Christoph Hellwig
2023-12-25  6:47                     ` Maxim Kochetkov
2023-12-25  6:47                       ` Maxim Kochetkov

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20231222041428.GA2803@lst.de \
    --to=hch@lst.de \
    --cc=aou@eecs.berkeley.edu \
    --cc=conor@kernel.org \
    --cc=fido_max@inbox.ru \
    --cc=jiaxun.yang@flygoat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-riscv@lists.infradead.org \
    --cc=mpe@ellerman.id.au \
    --cc=palmer@dabbelt.com \
    --cc=paul.walmsley@sifive.com \
    --cc=robh@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.