linux-kernel - Re: [PATCH] media: pwc: Fix the URB buffer allocation

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Message-ID: <YB1EXirrstMlg/vA@lunn.ch>
Date:   Fri, 5 Feb 2021 14:13:02 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     Hans Verkuil <hverkuil@...all.nl>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Matwey V. Kornilov" <matwey@....msu.ru>,
        Robert Foss <robert.foss@...aro.org>
Subject: Re: [PATCH] media: pwc: Fix the URB buffer allocation

Hi Takashi

> Indeed, looks so.  In most cases, this doesn't matter since both point
> to the same device object.  In some cases like xhci-plat HCD, they
> differ.  And sysdev  might be a better choice from the consistency
> POV.
> 
> But this brought an interesting question, too.  eg. USB chipidea
> HCD uses platform devices for both controller and sysdev, and I
> couldn't find any DMA mask setup.  So, no matter what to use, the uwc
> driver would be broken on this...  Maybe it's just not covered.

Did you do a git bisect to see what actually broke it?  "1161db6776bd:
media: usb: pwc: Don't use coherent DMA buffers for ISO transfer"
introduced the code, not the regression. If we understand the
regression, that might give us the answer about chipidea.

	    Andrew