From: Christoph Hellwig <hch@lst.de>
To: Guo Ren <guoren@kernel.org>
Cc: "Nick Kossifidis" <mick@ics.forth.gr>,
"Christoph Hellwig" <hch@lst.de>,
"Drew Fustini" <drew@beagleboard.org>,
"Anup Patel" <anup.patel@wdc.com>,
"Palmer Dabbelt" <palmerdabbelt@google.com>,
wefu@redhat.com, "Wei Wu (吴伟)" <lazyparser@gmail.com>,
linux-riscv <linux-riscv@lists.infradead.org>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
linux-arch <linux-arch@vger.kernel.org>,
linux-sunxi@lists.linux.dev, "Guo Ren" <guoren@linux.alibaba.com>,
"Paul Walmsley" <paul.walmsley@sifive.com>,
"Benjamin Koch" <snowball@c3pb.de>,
"Matteo Croce" <mcroce@linux.microsoft.com>,
"Wei Fu" <tekkamanninja@gmail.com>
Subject: Re: [PATCH RFC 0/3] riscv: Add DMA_COHERENT support
Date: Mon, 7 Jun 2021 08:27:01 +0200 [thread overview]
Message-ID: <20210607062701.GB24060@lst.de> (raw)
In-Reply-To: <CAJF2gTQuQ5bE6HeGSoNaDynA0o3+KEo4snwft42YGzE=+DjKOQ@mail.gmail.com>
On Mon, Jun 07, 2021 at 11:19:03AM +0800, Guo Ren wrote:
> >From Linux non-coherency view, we need:
> - Non-cache + Strong Order PTE attributes to deal with drivers' DMA descriptors
> - Non-cache + weak order to deal with framebuffer drivers
> - CMO dma_sync to sync cache with DMA devices
This is not strictly true. At the very minimum you only need cache
invalidation and writeback instructions. For example early parisc
CPUs and some m68knommu SOCs have no support for uncached areas at all,
and Linux works. But to be fair this is very painful and supports only
very limited periphals. So for modern full Linux support some uncahed
memory is advisable. But that doesn't have to be using PTE attributes.
It could also be physical memory regions that are either totally fixed
or somewhat dynamic.
WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@lst.de>
To: Guo Ren <guoren@kernel.org>
Cc: "Nick Kossifidis" <mick@ics.forth.gr>,
"Christoph Hellwig" <hch@lst.de>,
"Drew Fustini" <drew@beagleboard.org>,
"Anup Patel" <anup.patel@wdc.com>,
"Palmer Dabbelt" <palmerdabbelt@google.com>,
wefu@redhat.com, "Wei Wu (吴伟)" <lazyparser@gmail.com>,
linux-riscv <linux-riscv@lists.infradead.org>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
linux-arch <linux-arch@vger.kernel.org>,
linux-sunxi@lists.linux.dev, "Guo Ren" <guoren@linux.alibaba.com>,
"Paul Walmsley" <paul.walmsley@sifive.com>,
"Benjamin Koch" <snowball@c3pb.de>,
"Matteo Croce" <mcroce@linux.microsoft.com>,
"Wei Fu" <tekkamanninja@gmail.com>
Subject: Re: [PATCH RFC 0/3] riscv: Add DMA_COHERENT support
Date: Mon, 7 Jun 2021 08:27:01 +0200 [thread overview]
Message-ID: <20210607062701.GB24060@lst.de> (raw)
In-Reply-To: <CAJF2gTQuQ5bE6HeGSoNaDynA0o3+KEo4snwft42YGzE=+DjKOQ@mail.gmail.com>
On Mon, Jun 07, 2021 at 11:19:03AM +0800, Guo Ren wrote:
> >From Linux non-coherency view, we need:
> - Non-cache + Strong Order PTE attributes to deal with drivers' DMA descriptors
> - Non-cache + weak order to deal with framebuffer drivers
> - CMO dma_sync to sync cache with DMA devices
This is not strictly true. At the very minimum you only need cache
invalidation and writeback instructions. For example early parisc
CPUs and some m68knommu SOCs have no support for uncached areas at all,
and Linux works. But to be fair this is very painful and supports only
very limited periphals. So for modern full Linux support some uncahed
memory is advisable. But that doesn't have to be using PTE attributes.
It could also be physical memory regions that are either totally fixed
or somewhat dynamic.
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next prev parent reply other threads:[~2021-06-07 6:27 UTC|newest]
Thread overview: 112+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-19 5:04 [PATCH RFC 0/3] riscv: Add DMA_COHERENT support guoren
2021-05-19 5:04 ` guoren
2021-05-19 5:04 ` [PATCH RFC 1/3] riscv: pgtable.h: Fixup _PAGE_CHG_MASK usage guoren
2021-05-19 5:04 ` guoren
2021-05-19 5:04 ` [PATCH RFC 2/3] riscv: Add DMA_COHERENT for custom PTE attributes guoren
2021-05-19 5:04 ` guoren
2021-05-19 5:04 ` [PATCH RFC 3/3] riscv: Add SYNC_DMA_FOR_CPU/DEVICE for DMA_COHERENT guoren
2021-05-19 5:04 ` guoren
2021-05-19 6:32 ` Guo Ren
2021-05-19 6:32 ` Guo Ren
2021-05-19 5:20 ` [PATCH RFC 0/3] riscv: Add DMA_COHERENT support Christoph Hellwig
2021-05-19 5:20 ` Christoph Hellwig
2021-05-19 5:48 ` Guo Ren
2021-05-19 5:48 ` Guo Ren
2021-05-19 5:55 ` Christoph Hellwig
2021-05-19 5:55 ` Christoph Hellwig
2021-05-19 6:09 ` Guo Ren
2021-05-19 6:09 ` Guo Ren
2021-05-19 6:44 ` Drew Fustini
2021-05-19 6:44 ` Drew Fustini
2021-05-19 6:53 ` Christoph Hellwig
2021-05-19 6:53 ` Christoph Hellwig
2021-05-20 1:45 ` Guo Ren
2021-05-20 1:45 ` Guo Ren
2021-05-20 5:48 ` Christoph Hellwig
2021-05-20 5:48 ` Christoph Hellwig
2021-06-06 18:14 ` Nick Kossifidis
2021-06-06 18:14 ` Nick Kossifidis
2021-06-07 0:04 ` Guo Ren
2021-06-07 0:04 ` Guo Ren
2021-06-07 2:16 ` Nick Kossifidis
2021-06-07 2:16 ` Nick Kossifidis
2021-06-07 3:19 ` Guo Ren
2021-06-07 3:19 ` Guo Ren
2021-06-07 6:27 ` Christoph Hellwig [this message]
2021-06-07 6:27 ` Christoph Hellwig
2021-06-07 6:41 ` Guo Ren
2021-06-07 6:41 ` Guo Ren
2021-06-07 6:51 ` Christoph Hellwig
2021-06-07 6:51 ` Christoph Hellwig
2021-06-07 7:46 ` Guo Ren
2021-06-07 7:46 ` Guo Ren
2021-06-08 15:00 ` David Laight
2021-06-08 15:00 ` David Laight
2021-06-08 15:32 ` 'Christoph Hellwig'
2021-06-08 15:32 ` 'Christoph Hellwig'
2021-06-08 16:11 ` David Laight
2021-06-08 16:11 ` David Laight
2021-06-07 8:35 ` Nick Kossifidis
2021-06-07 8:35 ` Nick Kossifidis
2021-06-09 3:28 ` Guo Ren
2021-06-09 3:28 ` Guo Ren
2021-06-09 6:05 ` Jisheng Zhang
2021-06-09 6:05 ` Jisheng Zhang
2021-06-09 9:45 ` Nick Kossifidis
2021-06-09 9:45 ` Nick Kossifidis
2021-06-09 12:43 ` Guo Ren
2021-06-09 12:43 ` Guo Ren
2021-05-19 6:05 ` Guo Ren
2021-05-19 6:05 ` Guo Ren
2021-05-19 6:06 ` Christoph Hellwig
2021-05-19 6:06 ` Christoph Hellwig
2021-05-19 6:11 ` Guo Ren
2021-05-19 6:11 ` Guo Ren
2021-05-19 6:54 ` Drew Fustini
2021-05-19 6:54 ` Drew Fustini
2021-05-19 6:56 ` Christoph Hellwig
2021-05-19 6:56 ` Christoph Hellwig
2021-05-19 7:14 ` Anup Patel
2021-05-19 7:14 ` Anup Patel
2021-05-19 8:25 ` Damien Le Moal
2021-05-19 8:25 ` Damien Le Moal
2021-05-20 1:47 ` Guo Ren
2021-05-20 1:47 ` Guo Ren
2021-05-20 1:59 ` Guo Ren
2021-05-20 1:59 ` Guo Ren
2021-05-22 0:36 ` Guo Ren
2021-05-22 0:36 ` Guo Ren
2021-05-30 0:30 ` Palmer Dabbelt
2021-05-30 0:30 ` Palmer Dabbelt
2021-06-03 4:13 ` Palmer Dabbelt
2021-06-03 4:13 ` Palmer Dabbelt
2021-06-03 6:00 ` Anup Patel
2021-06-03 6:00 ` Anup Patel
2021-06-03 15:39 ` Palmer Dabbelt
2021-06-03 15:39 ` Palmer Dabbelt
2021-06-04 9:02 ` David Laight
2021-06-04 9:02 ` David Laight
2021-06-04 9:53 ` Arnd Bergmann
2021-06-04 9:53 ` Arnd Bergmann
2021-06-04 14:47 ` Guo Ren
2021-06-04 14:47 ` Guo Ren
2021-06-04 16:12 ` Palmer Dabbelt
2021-06-04 16:12 ` Palmer Dabbelt
2021-06-04 21:26 ` Arnd Bergmann
2021-06-04 21:26 ` Arnd Bergmann
2021-06-04 22:10 ` Palmer Dabbelt
2021-06-04 22:10 ` Palmer Dabbelt
2021-06-08 12:26 ` Guo Ren
2021-06-08 12:26 ` Guo Ren
2021-06-06 17:11 ` Guo Ren
2021-06-06 17:11 ` Guo Ren
2021-06-07 3:38 ` Anup Patel
2021-06-07 3:38 ` Anup Patel
2021-06-07 4:22 ` Guo Ren
2021-06-07 4:22 ` Guo Ren
2021-06-07 4:47 ` Anup Patel
2021-06-07 4:47 ` Anup Patel
2021-06-07 5:08 ` Guo Ren
2021-06-07 5:08 ` Guo Ren
2021-06-07 5:13 ` Guo Ren
2021-06-07 5:13 ` Guo Ren
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