From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Arnd Bergmann <arnd@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>, Vineet Gupta <vgupta@kernel.org>,
Russell King <linux@armlinux.org.uk>,
Neil Armstrong <neil.armstrong@linaro.org>,
Linus Walleij <linus.walleij@linaro.org>,
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John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
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Subject: Re: [PATCH 06/21] powerpc: dma-mapping: minimize for_cpu flushing
Date: Mon, 27 Mar 2023 12:56:33 +0000 [thread overview]
Message-ID: <52eef604-085e-acf9-f3ee-41ba9d8441d2@csgroup.eu> (raw)
In-Reply-To: <20230327121317.4081816-7-arnd@kernel.org>
Le 27/03/2023 à 14:13, Arnd Bergmann a écrit :
> From: Arnd Bergmann <arnd@arndb.de>
>
> The powerpc dma_sync_*_for_cpu() variants do more flushes than on other
> architectures. Reduce it to what everyone else does:
>
> - No flush is needed after data has been sent to a device
>
> - When data has been received from a device, the cache only needs to
> be invalidated to clear out cache lines that were speculatively
> prefetched.
>
> In particular, the second flushing of partial cache lines of bidirectional
> buffers is actively harmful -- if a single cache line is written by both
> the CPU and the device, flushing it again does not maintain coherency
> but instead overwrite the data that was just received from the device.
Hum ..... Who is right ?
That behaviour was introduced by commit 03d70617b8a7 ("powerpc: Prevent
memory corruption due to cache invalidation of unaligned DMA buffer")
I think your commit log should explain why that commit was wrong, and
maybe say that your patch is a revert of that commit ?
Christophe
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> arch/powerpc/mm/dma-noncoherent.c | 18 ++++--------------
> 1 file changed, 4 insertions(+), 14 deletions(-)
>
> diff --git a/arch/powerpc/mm/dma-noncoherent.c b/arch/powerpc/mm/dma-noncoherent.c
> index f10869d27de5..e108cacf877f 100644
> --- a/arch/powerpc/mm/dma-noncoherent.c
> +++ b/arch/powerpc/mm/dma-noncoherent.c
> @@ -132,21 +132,11 @@ void arch_sync_dma_for_cpu(phys_addr_t paddr, size_t size,
> switch (direction) {
> case DMA_NONE:
> BUG();
> - case DMA_FROM_DEVICE:
> - /*
> - * invalidate only when cache-line aligned otherwise there is
> - * the potential for discarding uncommitted data from the cache
> - */
> - if ((start | end) & (L1_CACHE_BYTES - 1))
> - __dma_phys_op(start, end, DMA_CACHE_FLUSH);
> - else
> - __dma_phys_op(start, end, DMA_CACHE_INVAL);
> - break;
> - case DMA_TO_DEVICE: /* writeback only */
> - __dma_phys_op(start, end, DMA_CACHE_CLEAN);
> + case DMA_TO_DEVICE:
> break;
> - case DMA_BIDIRECTIONAL: /* writeback and invalidate */
> - __dma_phys_op(start, end, DMA_CACHE_FLUSH);
> + case DMA_FROM_DEVICE:
> + case DMA_BIDIRECTIONAL:
> + __dma_phys_op(start, end, DMA_CACHE_INVAL);
> break;
> }
> }
next prev parent reply other threads:[~2023-03-27 12:57 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 [this message]
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
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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