From: Christoph Hellwig <hch@lst.de>
To: Greg Ungerer <gerg@kernel.org>
Cc: Angelo Dureghello <adureghello@baylibre.com>,
Arnd Bergmann <arnd@kernel.org>,
linux-m68k@lists.linux-m68k.org, linux-kernel@vger.kernel.org,
dmaengine@vger.kernel.org, linux-can@vger.kernel.org,
linux-spi@vger.kernel.org, Vladimir Oltean <olteanv@gmail.com>,
Christoph Hellwig <hch@lst.de>
Subject: Re: [RFC 4/4] m68k: coldfire: fix non-standard readX()/writeX() functions
Date: Mon, 1 Jun 2026 16:43:32 +0200 [thread overview]
Message-ID: <20260601144332.GC4918@lst.de> (raw)
In-Reply-To: <2b532d56-dce4-4f6d-84e0-2fd87d5494f8@kernel.org>
On Sun, May 31, 2026 at 11:42:26PM +1000, Greg Ungerer wrote:
> I don't think that is right. The way the underlying data cache is setup for
> MMU ColdFire (via the ACR/CACR registers) means that individual pages cannot
> be marked as non-cached. So coherent memory allocations are not possible -
> at least the way things are today.
>
> It would be possible to set aside a chunk of RAM at kernel startup time
> to use as a pool for coherent allocations (since it could be marked as
> non-cached via the ACR/CACR registers), but there is no code to support doing
> that today.
With CONFIG_DMA_GLOBAL_POOL there is some generic code dealing with
most of this. But if this driver worked on coldfire in the past,
it must have been fine with non-coherent memory and could use the
non-coherent allocator.
next prev parent reply other threads:[~2026-06-01 14:43 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20260506142644.3234270-2-gerg@kernel.org>
2026-05-06 14:26 ` [RFC 4/4] m68k: coldfire: fix non-standard readX()/writeX() functions Greg Ungerer
2026-05-06 16:14 ` Frank Li
2026-05-06 19:12 ` Arnd Bergmann
2026-05-07 12:43 ` Greg Ungerer
2026-05-07 12:59 ` Arnd Bergmann
2026-05-17 19:43 ` Angelo Dureghello
2026-05-17 20:08 ` Arnd Bergmann
2026-05-17 22:04 ` Angelo Dureghello
2026-05-17 22:41 ` Angelo Dureghello
2026-05-24 21:17 ` Angelo Dureghello
2026-05-24 21:34 ` Angelo Dureghello
2026-05-25 13:39 ` Angelo Dureghello
2026-05-31 13:42 ` Greg Ungerer
2026-06-01 14:43 ` Christoph Hellwig [this message]
2026-05-07 13:30 ` Marc Kleine-Budde
2026-05-07 14:33 ` Greg Ungerer
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