linux-kernel - Re: [PATCH 6/6] media: uvcvideo: Use dma_alloc

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Date:   Thu, 28 Jan 2021 18:00:57 +0100
From:   Ricardo Ribalda <ribalda@...omium.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Sergey Senozhatsky <senozhatsky@...gle.com>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Robin Murphy <robin.murphy@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>
Subject: Re: [PATCH 6/6] media: uvcvideo: Use dma_alloc_noncontiguos API

HI Christoph

Thanks for your comments

On Thu, Jan 28, 2021 at 4:09 PM Christoph Hellwig <hch@....de> wrote:
>
> I just included this patch as-is, but here are a few comments:
>
> On Thu, Jan 28, 2021 at 03:58:37PM +0100, Christoph Hellwig wrote:
> > +static void uvc_urb_dma_sync(struct uvc_urb *uvc_urb, bool for_device)
> > +{
> > +     struct device *dma_dev = dma_dev = stream_to_dmadev(uvc_urb->stream);
> > +
> > +     if (for_device)
> > +             dma_sync_sgtable_for_device(dma_dev, uvc_urb->sgt,
> > +                                         DMA_FROM_DEVICE);
> > +     else
> > +             dma_sync_sgtable_for_cpu(dma_dev, uvc_urb->sgt,
> > +                                      DMA_FROM_DEVICE);
> > +}
>
> Given that we vmap the addresses this also needs
> flush_kernel_vmap_range / invalidate_kernel_vmap_range calls for
> VIVT architectures.

We only read from the device to the cpu. Then can we run only
invalidate_kernel_vmap_range() ?

something like ?
else {
          dma_sync_sgtable_for_cpu(dma_dev, uvc_urb->sgt, DMA_FROM_DEVICE);
           invalidate_kernel_vmap_range(uvc_urb->buffer,
uvc_urb->stream->urb_size );
}

Thanks!






--
Ricardo Ribalda