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

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Message-ID: <YB0/wTjYqE9IgtXZ@lunn.ch>
Date:   Fri, 5 Feb 2021 13:53:21 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     Takashi Iwai <tiwai@...e.de>,
        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

On Fri, Feb 05, 2021 at 01:36:43PM +0100, Hans Verkuil wrote:
> Hi Takashi,
> 
> Thank you for this patch, but it clashes with another patch trying to do the same thing
> that has already been merged in our tree:
> 
> https://patchwork.linuxtv.org/project/linux-media/patch/20210104170007.20625-1-matwey@sai.msu.ru/
> 
> I do prefer your patch over the one already merged since it is a bit simpler, but
> shouldn't the calls to dma_sync_single_for_cpu() and dma_sync_single_for_device()
> in pwc-if.c also use urb->dev->bus->controller?
> 
> Also, Matwey's patch uses urb->dev->bus->sysdev instead of urb->dev->bus->controller.
> How does 'sysdev' relate to 'controller'? I think 'controller' is the right device to
> use, but either seems to work when I test it with my pwc webcam.

Hi Hans

A quick grep in driver/usb show that all but one dma mapping operation
use sysdev. The one other case uses controller. So the numbers suggest
controller is wrong, sysdev is correct.

But maybe ask GregKH?

	   Andrew