From: "Arnd Bergmann" <arnd@arndb.de>
To: "Ben Collins" <bcollins@kernel.org>
Cc: dmaengine@vger.kernel.org, "Vinod Koul" <vkoul@kernel.org>,
linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
"Robin Murphy" <robin.murphy@arm.com>
Subject: Re: [PATCH] fsldma: Support 40 bit DMA addresses where capable
Date: Wed, 23 Apr 2025 22:56:01 +0200 [thread overview]
Message-ID: <7d914aa8-dc6f-426c-b7fc-dbb03c6b676c@app.fastmail.com> (raw)
In-Reply-To: <2025042316-nippy-lemur-debd6b@boujee-and-buff>
On Wed, Apr 23, 2025, at 22:41, Ben Collins wrote:
> On Wed, Apr 23, 2025 at 03:49:16PM -0500, Arnd Bergmann wrote:
>> Looking at the current code I don't see that any more, so it's
>> possible that now any DMA is allowed even if there is no
>> dma-ranges property at all.
>
> It's still there. It hardcodes zone_dma_limit to 31-bits:
>
> arch/powerpc/mm/mem.c: paging_init()
>
> I'm digging into this more. I'll check back when I have a better
> understanding.
zone_dma_limit is the other side of this: you need a ZONE_DMA
and/or ZONE_DMA32 memory zone that lets a driver allocate buffers
from low addresses if the DMA mask is smaller than the available
memory.
Arnd
prev parent reply other threads:[~2025-04-23 20:56 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-04-22 2:49 [PATCH] fsldma: Support 40 bit DMA addresses where capable Ben Collins
2025-04-22 6:34 ` Arnd Bergmann
2025-04-22 7:12 ` Ben Collins
2025-04-22 7:59 ` Arnd Bergmann
2025-04-22 8:56 ` Ben Collins
2025-04-22 9:25 ` Arnd Bergmann
2025-04-22 21:10 ` Ben Collins
2025-04-23 13:49 ` Arnd Bergmann
2025-04-23 20:41 ` Ben Collins
2025-04-23 20:56 ` Arnd Bergmann [this message]
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