linux-kernel - Re: [PATCH 2/3] dma-mapping: don't return errors from dma_set_seg

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Message-ID: <a1a07edf-9ab2-4121-a230-0d06bda3bf3d@arm.com>
Date: Fri, 2 Aug 2024 12:53:01 +0100
From: Robin Murphy <robin.murphy@....com>
To: Christoph Hellwig <hch@....de>
Cc: Marek Szyprowski <m.szyprowski@...sung.com>, iommu@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] dma-mapping: don't return errors from
 dma_set_seg_boundary

On 01/08/2024 2:33 pm, Christoph Hellwig wrote:
> On Thu, Aug 01, 2024 at 01:36:01PM +0100, Robin Murphy wrote:
>> I guess I assumed that the old block layer bodges in this area had been
>> cleaned up already - perhaps it *is* high time for whatever's left to grow
>> a proper understanding of whether a block device actually does its own DMA
>> or not.
> 
> Can you point to a discussion on that?  The concepts here don't make
> quite sense to me.

No specific discussion, I just have a vague memory of hacks in the USB 
layer when I first started looking at this stuff 10 years ago... From a 
bit of digging to try to remind myself, I'm fairly sure that must have 
been the block bounce related stuff, which you cleaned up in 
6eb0233ec2d0 ("usb: don't inherity DMA properties for USB devices") a 
while back.

Cheers,
Robin.