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

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Date:   Fri, 5 Feb 2021 13:36:43 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Matwey V. Kornilov" <matwey@....msu.ru>,
        Andrew Lunn <andrew@...n.ch>,
        Robert Foss <robert.foss@...aro.org>
Subject: Re: [PATCH] media: pwc: Fix the URB buffer allocation

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.

Andrew, your patch:

https://patchwork.linuxtv.org/project/linux-media/patch/20210204232851.1020416-1-andrew@lunn.ch/

is effectively identical to Takashi's, so I'll mark your patch as Obsoleted.
Just so you know :-)

Regards,

	Hans

On 21/01/2021 21:28, Takashi Iwai wrote:
> The URB buffer allocation of pwc driver involves with the
> dma_map_single(), and it needs to pass the right device.  Currently it
> passes usb_device.dev, but it's no real device that manages the DMA.
> Since the passed device has no DMA mask set up, now the pwc driver
> hits the WARN_ON_ONCE() check in dma_map_page_attrs() (that was
> introduced in 5.10), resulting in an error at URB allocations.
> Eventually this ended up with the black output.
> 
> This patch fixes the bug by passing the proper device, the bus
> controller, to make the URB allocation and map working again.
> 
> BugLink: https://bugzilla.suse.com/show_bug.cgi?id=1181133
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Takashi Iwai <tiwai@...e.de>
> ---
>  drivers/media/usb/pwc/pwc-if.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/usb/pwc/pwc-if.c b/drivers/media/usb/pwc/pwc-if.c
> index 61869636ec61..d771160bb168 100644
> --- a/drivers/media/usb/pwc/pwc-if.c
> +++ b/drivers/media/usb/pwc/pwc-if.c
> @@ -461,7 +461,7 @@ static int pwc_isoc_init(struct pwc_device *pdev)
>  		urb->pipe = usb_rcvisocpipe(udev, pdev->vendpoint);
>  		urb->transfer_flags = URB_ISO_ASAP | URB_NO_TRANSFER_DMA_MAP;
>  		urb->transfer_buffer_length = ISO_BUFFER_SIZE;
> -		urb->transfer_buffer = pwc_alloc_urb_buffer(&udev->dev,
> +		urb->transfer_buffer = pwc_alloc_urb_buffer(udev->bus->controller,
>  							    urb->transfer_buffer_length,
>  							    &urb->transfer_dma);
>  		if (urb->transfer_buffer == NULL) {
> @@ -524,7 +524,7 @@ static void pwc_iso_free(struct pwc_device *pdev)
>  		if (urb) {
>  			PWC_DEBUG_MEMORY("Freeing URB\n");
>  			if (urb->transfer_buffer)
> -				pwc_free_urb_buffer(&urb->dev->dev,
> +				pwc_free_urb_buffer(urb->dev->bus->controller,
>  						    urb->transfer_buffer_length,
>  						    urb->transfer_buffer,
>  						    urb->transfer_dma);
>