From: "Arnd Bergmann" <arnd@arndb.de>
To: "Russell King" <linux@armlinux.org.uk>,
"Arnd Bergmann" <arnd@kernel.org>
Cc: linux-kernel@vger.kernel.org, "Vineet Gupta" <vgupta@kernel.org>,
"Neil Armstrong" <neil.armstrong@linaro.org>,
"Linus Walleij" <linus.walleij@linaro.org>,
"Catalin Marinas" <catalin.marinas@arm.com>,
"Will Deacon" <will@kernel.org>, guoren <guoren@kernel.org>,
"Brian Cain" <bcain@quicinc.com>,
"Geert Uytterhoeven" <geert@linux-m68k.org>,
"Michal Simek" <monstr@monstr.eu>,
"Thomas Bogendoerfer" <tsbogend@alpha.franken.de>,
"Dinh Nguyen" <dinguyen@kernel.org>,
"Stafford Horne" <shorne@gmail.com>,
"Helge Deller" <deller@gmx.de>,
"Michael Ellerman" <mpe@ellerman.id.au>,
"Christophe Leroy" <christophe.leroy@csgroup.eu>,
"Paul Walmsley" <paul.walmsley@sifive.com>,
"Palmer Dabbelt" <palmer@dabbelt.com>,
"Rich Felker" <dalias@libc.org>,
"John Paul Adrian Glaubitz" <glaubitz@physik.fu-berlin.de>,
"David S . Miller" <davem@davemloft.net>,
"Max Filippov" <jcmvbkbc@gmail.com>,
"Christoph Hellwig" <hch@lst.de>,
"Robin Murphy" <robin.murphy@arm.com>,
"Lad, Prabhakar" <prabhakar.mahadev-lad.rj@bp.renesas.com>,
"Conor.Dooley" <conor.dooley@microchip.com>,
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"linux-openrisc@vger.kernel.org" <linux-openrisc@vger.kernel.org>,
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Subject: Re: [PATCH 20/21] ARM: dma-mapping: split out arch_dma_mark_clean() helper
Date: Fri, 31 Mar 2023 16:06:37 +0200 [thread overview]
Message-ID: <1be05746-9deb-49cb-b106-71b2db8318cd@app.fastmail.com> (raw)
In-Reply-To: <ZCGv18wnEtoFvtfM@shell.armlinux.org.uk>
On Mon, Mar 27, 2023, at 17:01, Russell King (Oracle) wrote:
> On Mon, Mar 27, 2023 at 02:13:16PM +0200, Arnd Bergmann wrote:
>> From: Arnd Bergmann <arnd@arndb.de>
>>
>> The arm version of the arch_sync_dma_for_cpu() function annotates pages as
>> PG_dcache_clean after a DMA, but no other architecture does this here.
>
> ... because this is an arm32 specific feature. Generically, it's
> PG_arch_1, which is a page flag free for architecture use. On arm32
> we decided to use this to mark whether we can skip dcache writebacks
> when establishing a PTE - and thus it was decided to call it
> PG_dcache_clean to reflect how arm32 decided to use that bit.
>
> This isn't just a DMA thing, there are other places that we update
> the bit, such as flush_dcache_page() and copy_user_highpage().
>
> So thinking that the arm32 PG_dcache_clean is something for DMA is
> actually wrong.
>
> Other architectures are free to do their own other optimisations
> using that bit, and their implementations may be DMA-centric.
The flag is used the same way on most architectures, though some
use the opposite polarity and call it PG_dcache_dirty. The only
other architecture that uses it for DMA is ia64, with the difference
being that this also marks the page as clean even for coherent
DMA, not just when doing a flush as part of noncoherent DMA.
Based on Robin's reply it sounds that this is not a valid assumption
on Arm, if a coherent DMA can target a dirty dcache line without
cleaning it.
Arnd
next prev parent reply other threads:[~2023-03-31 14:07 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-27 12:12 [PATCH 00/21] dma-mapping: unify support for cache flushes Arnd Bergmann
2023-03-27 12:12 ` [PATCH 01/21] openrisc: dma-mapping: flush bidirectional mappings Arnd Bergmann
2023-03-27 12:12 ` [PATCH 02/21] xtensa: dma-mapping: use normal cache invalidation rules Arnd Bergmann
2023-03-27 15:42 ` Max Filippov
2023-03-27 12:12 ` [PATCH 03/21] sparc32: flush caches in dma_sync_*for_device Arnd Bergmann
2023-03-27 12:13 ` [PATCH 04/21] microblaze: dma-mapping: skip extra DMA flushes Arnd Bergmann
2023-03-27 12:13 ` [PATCH 05/21] powerpc: dma-mapping: split out cache operation logic Arnd Bergmann
2023-03-27 12:13 ` [PATCH 06/21] powerpc: dma-mapping: minimize for_cpu flushing Arnd Bergmann
2023-03-27 12:56 ` Christophe Leroy
2023-03-27 13:02 ` Arnd Bergmann
2023-03-27 12:13 ` [PATCH 07/21] powerpc: dma-mapping: always clean cache in _for_device() op Arnd Bergmann
2023-03-27 12:13 ` [PATCH 08/21] riscv: dma-mapping: only invalidate after DMA, not flush Arnd Bergmann
2023-03-29 20:48 ` Conor Dooley
2023-03-30 7:10 ` Arnd Bergmann
2023-03-29 21:51 ` Jessica Clarke
2023-03-30 12:59 ` Lad, Prabhakar
2023-04-19 14:22 ` Palmer Dabbelt
2023-03-27 12:13 ` [PATCH 09/21] riscv: dma-mapping: skip invalidation before bidirectional DMA Arnd Bergmann
2023-03-29 20:16 ` Conor Dooley
2023-03-30 13:26 ` Lad, Prabhakar
2023-04-19 14:22 ` Palmer Dabbelt
2023-05-05 5:47 ` Guo Ren
2023-05-05 13:18 ` Arnd Bergmann
2023-05-06 7:25 ` Guo Ren
2023-05-06 7:53 ` Arnd Bergmann
2023-03-27 12:13 ` [PATCH 10/21] csky: dma-mapping: skip invalidating before DMA from device Arnd Bergmann
2023-03-27 13:37 ` Guo Ren
2023-03-27 12:13 ` [PATCH 11/21] mips: dma-mapping: skip invalidating before bidirectional DMA Arnd Bergmann
2023-03-27 12:13 ` [PATCH 12/21] mips: dma-mapping: split out cache operation logic Arnd Bergmann
2023-03-27 12:13 ` [PATCH 13/21] arc: dma-mapping: skip invalidating before bidirectional DMA Arnd Bergmann
2023-04-02 6:52 ` Vineet Gupta
2023-04-04 8:27 ` Shahab Vahedi
2023-04-06 9:01 ` Shahab Vahedi
2023-03-27 12:13 ` [PATCH 14/21] parisc: dma-mapping: use regular flush/invalidate ops Arnd Bergmann
2023-03-27 12:13 ` [PATCH 15/21] ARM: dma-mapping: always invalidate WT caches before DMA Arnd Bergmann
2023-03-31 9:01 ` Linus Walleij
2023-03-31 9:07 ` Russell King (Oracle)
2023-03-31 9:35 ` Russell King (Oracle)
2023-03-31 10:38 ` Arnd Bergmann
2023-03-31 11:08 ` Russell King (Oracle)
2023-03-31 12:32 ` Arnd Bergmann
2023-03-27 12:13 ` [PATCH 16/21] ARM: dma-mapping: bring back dmac_{clean,inv}_range Arnd Bergmann
2023-03-27 13:10 ` Russell King (Oracle)
2023-03-27 12:13 ` [PATCH 17/21] ARM: dma-mapping: use arch_sync_dma_for_{device,cpu}() internally Arnd Bergmann
2023-03-31 9:10 ` Linus Walleij
2023-03-31 12:48 ` Arnd Bergmann
2023-03-27 12:13 ` [PATCH 18/21] ARM: drop SMP support for ARM11MPCore Arnd Bergmann
2023-03-30 7:48 ` Neil Armstrong
2023-03-30 10:03 ` Arnd Bergmann
2023-03-30 16:40 ` Neil Armstrong
2023-03-30 8:12 ` Linus Walleij
2023-03-30 11:51 ` Ard Biesheuvel
2023-03-31 17:09 ` Catalin Marinas
2023-03-27 12:13 ` [PATCH 19/21] ARM: dma-mapping: use generic form of arch_sync_dma_* helpers Arnd Bergmann
2023-03-27 12:13 ` [PATCH 20/21] ARM: dma-mapping: split out arch_dma_mark_clean() helper Arnd Bergmann
2023-03-27 12:48 ` Robin Murphy
2023-03-31 14:00 ` Arnd Bergmann
2023-03-31 15:12 ` Robin Murphy
2023-03-31 17:20 ` Arnd Bergmann
2023-03-27 15:01 ` Russell King (Oracle)
2023-03-31 14:06 ` Arnd Bergmann [this message]
2023-03-31 15:54 ` Russell King (Oracle)
2023-07-03 7:54 ` Geert Uytterhoeven
2023-07-06 14:11 ` Christoph Hellwig
2023-03-27 12:13 ` [PATCH 21/21] dma-mapping: replace custom code with generic implementation Arnd Bergmann
2023-03-27 22:25 ` Christoph Hellwig
2023-03-31 13:04 ` Arnd Bergmann
2023-03-30 14:06 ` Lad, Prabhakar
2023-04-13 12:13 ` Biju Das
2023-04-13 12:51 ` Arnd Bergmann
2023-06-27 16:52 ` Geert Uytterhoeven
2023-03-31 16:53 ` [PATCH 00/21] dma-mapping: unify support for cache flushes Catalin Marinas
2023-03-31 20:27 ` Arnd Bergmann
2023-05-25 7:46 ` Lad, Prabhakar
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