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    SubjectRe: [PATCH] media: pwc: Fix the URB buffer allocation
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    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@vger.kernel.org>
    > Signed-off-by: Takashi Iwai <tiwai@suse.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);
    >

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