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From: Conor Dooley <conor@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Conor Dooley <conor.dooley@microchip.com>,
	Greg Ungerer <gerg@linux-m68k.org>,
	iommu@lists.linux.dev, Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	Magnus Damm <magnus.damm@gmail.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Wei Fang <wei.fang@nxp.com>, Shenwei Wang <shenwei.wang@nxp.com>,
	Clark Wang <xiaoning.wang@nxp.com>,
	NXP Linux Team <linux-imx@nxp.com>,
	linux-m68k@lists.linux-m68k.org, netdev@vger.kernel.org,
	linux-riscv@lists.infradead.org,
	linux-renesas-soc@vger.kernel.org,
	Jim Quinlan <james.quinlan@broadcom.com>
Subject: Re: [PATCH 01/12] riscv: RISCV_NONSTANDARD_CACHE_OPS shouldn't depend on RISCV_DMA_NONCOHERENT
Date: Mon, 16 Oct 2023 18:16:20 +0100	[thread overview]
Message-ID: <20231016-outwit-bungee-b46cf212c292@spud> (raw)
In-Reply-To: <20231016131716.GA26484@lst.de>


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On Mon, Oct 16, 2023 at 03:17:16PM +0200, Christoph Hellwig wrote:
> On Mon, Oct 16, 2023 at 01:49:41PM +0100, Conor Dooley wrote:
> > Hey,
> > 
> > On Mon, Oct 16, 2023 at 07:47:43AM +0200, Christoph Hellwig wrote:
> > > RISCV_NONSTANDARD_CACHE_OPS is also used for the pmem cache maintenance
> > > helpers, which are built into the kernel unconditionally.
> > 
> > You surely have better insight than I do here, but is this actually
> > required?
> > This patch seems to allow creation of a kernel where the cache
> > maintenance operations could be used for pmem, but would be otherwise
> > unavailable, which seems counter intuitive to me.
> >
> > Why would someone want to provide the pmem helpers with cache
> > maintenance operations, but not provide them generally?
> > 
> 
> Even if all your periphals are cache coherent (very common on server
> class hardware) you still need cache maintenance for pmem.  No need
> to force the extra text size and runtime overhead for non-coherent DMA.

Ah, right.

> > I also don't really understand what the unconditional nature of the pmem
> > helpers has to do with anything, as this patch does not unconditionally
> > provide any cache management operations, only relax the conditions under
> > which the non-standard cache management operations can be provided.
> 
> They simply were broken if a platform had non-standard cache mem but
> only coherent DMA before.  That's probably more a theoretical than
> practial case, but still worth fixing.

And this part of it makes more sense with the above use-case explained.

Acked-by: Conor Dooley <conor.dooley@microchip.com>

Thanks,
Conor.


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  reply	other threads:[~2023-10-16 17:16 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-10-16  5:47 fix the non-coherent coldfire dma_alloc_coherent v2 Christoph Hellwig
2023-10-16  5:47 ` [PATCH 01/12] riscv: RISCV_NONSTANDARD_CACHE_OPS shouldn't depend on RISCV_DMA_NONCOHERENT Christoph Hellwig
2023-10-16 12:49   ` Conor Dooley
2023-10-16 13:17     ` Christoph Hellwig
2023-10-16 17:16       ` Conor Dooley [this message]
2023-10-16  5:47 ` [PATCH 02/12] riscv: only select DMA_DIRECT_REMAP from RISCV_ISA_ZICBOM Christoph Hellwig
2023-10-16 11:18   ` Robin Murphy
2023-10-16 12:55   ` Conor Dooley
2023-10-16 15:39   ` Lad, Prabhakar
2023-10-16  5:47 ` [PATCH 03/12] soc: renesas: ARCH_R9A07G043 depends on !RISCV_ISA_ZICBOM Christoph Hellwig
2023-10-16 12:53   ` Conor Dooley
2023-10-16 15:40   ` Lad, Prabhakar
2023-10-17  7:59   ` Geert Uytterhoeven
2023-10-16  5:47 ` [PATCH 04/12] soc: renesas: select RISCV_DMA_NONCOHERENT from ARCH_R9A07G043 Christoph Hellwig
2023-10-16 12:52   ` Conor Dooley
2023-10-16 13:17     ` Christoph Hellwig
2023-10-17 10:44       ` Geert Uytterhoeven
2023-10-17 12:46         ` Christoph Hellwig
2023-10-17 13:12           ` Geert Uytterhoeven
2023-10-16 15:42   ` Lad, Prabhakar
2023-10-17  8:20   ` Geert Uytterhoeven
2023-10-16  5:47 ` [PATCH 05/12] dma-direct: add depdenencies to CONFIG_DMA_GLOBAL_POOL Christoph Hellwig
2023-10-16 11:18   ` Robin Murphy
2023-10-16 15:44   ` Lad, Prabhakar
2023-10-16  5:47 ` [PATCH 06/12] dma-direct: add a CONFIG_ARCH_DMA_ALLOC symbol Christoph Hellwig
2023-10-16 11:33   ` Robin Murphy
2023-10-16  5:47 ` [PATCH 07/12] dma-direct: simplify the use atomic pool logic in dma_direct_alloc Christoph Hellwig
2023-10-16 11:58   ` Robin Murphy
2023-10-16  5:47 ` [PATCH 08/12] dma-direct: warn when coherent allocations aren't supported Christoph Hellwig
2023-10-16 11:59   ` Robin Murphy
2023-10-16  5:47 ` [PATCH 09/12] m68k: use the coherent DMA code for coldfire without data cache Christoph Hellwig
2023-10-17  8:40   ` Geert Uytterhoeven
2023-10-19 12:50   ` Greg Ungerer
2023-10-16  5:47 ` [PATCH 10/12] net: fec: use dma_alloc_noncoherent for data cache enabled coldfire Christoph Hellwig
2023-10-17  8:43   ` Geert Uytterhoeven
2023-10-16  5:47 ` [PATCH 11/12] m68k: don't provide arch_dma_alloc for nommu/coldfire Christoph Hellwig
2023-10-16  5:47 ` [PATCH 12/12] m68k: remove unused includes from dma.c Christoph Hellwig
2023-10-17  8:48   ` Geert Uytterhoeven
2023-10-19 13:09 ` fix the non-coherent coldfire dma_alloc_coherent v2 Greg Ungerer

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