linux-kernel - Re: [PATCH] drm/test/shmem: set a DMA mask for the mock device

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Message-ID: <ut2c26ig4e6pbtvszmfm34h4ev3oflwkz3mwkjtqaxlpethwfk@w3bnhg4iw4mn>
Date: Tue, 27 Feb 2024 17:25:46 +0100
From: Maxime Ripard <mripard@...nel.org>
To: Marco Pagani <marpagan@...hat.com>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
	Daniel Vetter <daniel@...ll.ch>, Guenter Roeck <linux@...ck-us.net>, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/test/shmem: set a DMA mask for the mock device

Hi,

On Mon, Feb 26, 2024 at 04:48:51PM +0100, Marco Pagani wrote:
> 
> On 2024-02-26 12:26, Maxime Ripard wrote:
> > Hi,
> > 
> > On Mon, Feb 26, 2024 at 12:00:27PM +0100, Marco Pagani wrote:
> >> Set a DMA mask for the mock device to avoid warnings generated in
> >> dma_map_sgtable().
> >>
> >> Reported-by: Guenter Roeck <linux@...ck-us.net>
> >> Signed-off-by: Marco Pagani <marpagan@...hat.com>
> > 
> > I've submitted last week this patch:
> > https://lore.kernel.org/all/20240221125324.718192-1-mripard@kernel.org/
> > 
> > Which should be equivalent, but fixes the issue for all users in the
> > tree.
> 
> Hi, thanks for letting me know. Fixing this issue for all DRM tests that were
> using platform devices through the helpers makes perfect sense to me. I'm a
> little more thoughtful about setting the mask for all KUnit tests that use fake
> devices since there may be specific use cases. Just one curiosity: why setting
> the default mask manually instead of using one of the dma_set_*() functions?

I think the (well, mine at least) expectation is that a kunit device is
a device that can be used in all reasonable contexts. Setting up the
device to be able to use any DMA-related function (or functions that use
a DMA-related function) makes total sense to me.

But it's a discussion worth having I think, so it would make sense to
raise this point with the kunit maintainers if you feel like it.

Maxime

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