From: Christoph Hellwig <hch@lst.de>
To: Will Deacon <will@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org,
Catalin Marinas <catalin.marinas@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Robin Murphy <robin.murphy@arm.com>,
Christoph Hellwig <hch@lst.de>, Ard Biesheuvel <ardb@kernel.org>
Subject: Re: [PATCH] arm64: dma: Drop cache invalidation from arch_dma_prep_coherent()
Date: Wed, 7 Sep 2022 11:03:05 +0200 [thread overview]
Message-ID: <20220907090305.GA30704@lst.de> (raw)
In-Reply-To: <20220823122111.17439-1-will@kernel.org>
On Tue, Aug 23, 2022 at 01:21:11PM +0100, Will Deacon wrote:
> arch_dma_prep_coherent() is called when preparing a non-cacheable region
> for a consistent DMA buffer allocation. Since the buffer pages may
> previously have been written via a cacheable mapping and consequently
> allocated as dirty cachelines, the purpose of this function is to remove
> these dirty lines from the cache, writing them back so that the
> non-coherent device is able to see them.
Yes.
> I'm slightly wary about this change as other architectures seem to do
> clean+invalidate here, but I'd like to hear what others think in any
> case.
If arm64 is fine with having clean but present cachelines when creating
an uncached mapping for a cache line, the invalidate is not required.
But isn't it better for the cache if these by definition useless
cachelines get evicted?
My biggest concern here is that we're now moving from consolidating
these semantics in all the different architectures to different ones,
making a centralization of the policies even harder.
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2022-09-07 9:12 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-23 12:21 [PATCH] arm64: dma: Drop cache invalidation from arch_dma_prep_coherent() Will Deacon
2022-08-24 9:58 ` Ard Biesheuvel
2022-08-24 11:23 ` Will Deacon
2022-08-24 11:49 ` Ard Biesheuvel
2022-08-24 22:00 ` Catalin Marinas
2022-09-07 9:04 ` Christoph Hellwig
2022-09-07 14:10 ` Russell King (Oracle)
2022-09-07 14:14 ` Christoph Hellwig
2022-09-07 14:15 ` Russell King (Oracle)
2022-09-07 9:03 ` Christoph Hellwig [this message]
2022-09-07 9:27 ` Robin Murphy
2022-09-07 16:25 ` Will Deacon
2022-09-07 17:50 ` Robin Murphy
2022-09-08 10:32 ` Catalin Marinas
2022-09-08 11:32 ` Robin Murphy
2022-09-08 13:02 ` Catalin Marinas
2022-09-08 13:27 ` Catalin Marinas
2022-09-08 13:32 ` Will Deacon
2022-09-08 15:49 ` Catalin Marinas
2022-09-07 16:28 ` Will Deacon
2022-09-22 20:02 ` Catalin Marinas
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=20220907090305.GA30704@lst.de \
--to=hch@lst.de \
--cc=ardb@kernel.org \
--cc=catalin.marinas@arm.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=mark.rutland@arm.com \
--cc=robin.murphy@arm.com \
--cc=will@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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).