linux-kernel - Re: [PATCH] dma/mapping.c: dev_dbg support for dma_addressing

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Message-ID: <f909b34f-784c-4439-928a-fe00ac34fb35@nvidia.com>
Date: Mon, 14 Apr 2025 21:36:51 +1000
From: Balbir Singh <balbirs@...dia.com>
To: Christoph Hellwig <hch@...radead.org>
Cc: iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
 Marek Szyprowski <m.szyprowski@...sung.com>,
 Robin Murphy <robin.murphy@....com>,
 Christian König <christian.koenig@....com>,
 Ingo Molnar <mingo@...nel.org>, Kees Cook <kees@...nel.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 Peter Zijlstra <peterz@...radead.org>, Andy Lutomirski <luto@...nel.org>,
 Alex Deucher <alexander.deucher@....com>, Bert Karwatzki <spasswolf@....de>
Subject: Re: [PATCH] dma/mapping.c: dev_dbg support for dma_addressing_limited

On 4/14/25 21:14, Christoph Hellwig wrote:
> On Mon, Apr 14, 2025 at 09:06:46PM +1000, Balbir Singh wrote:
>> +	dev_dbg(dev, "might have lower perf due to bounce buffering\n");
> 
> I don't think that's a good message.  Report the actual observation,
> i.e. "device is DMA addressing limited" and not a guessed conclusion.
> 

The bounce buffering remark came from the rest of the mention in code
and I agree the perf is based on my experience and may not be true
in all cases.

I'll respin

Balbir