Re: [PATCH v5 2/2] media: usb: pwc: Don't use coherent DMA buffers for ISO transfer

[Tomasz Figa]

On Wed, Dec 19, 2018 at 11:51 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
>
> On Wed, Dec 19, 2018 at 05:18:35PM +0900, Tomasz Figa wrote:
> > The existing code that deals with dma_alloc_attrs() without
> > DMA_ATTR_NON_CONSISTENT would just call dma_get_sgtable_attrs() like
> > here:
>
> I know.  And dma_get_sgtable_attrs is fundamentally flawed and we
> need to kill this interface as it just can't worked with virtually
> tagged cases.  It is a prime example for an interface that looks
> nice and simple but is plain wrong.

Got it, thanks.

I haven't been following the problems with virtually tagged cases,
would you mind sharing some background, so that we can consider it
when adding non-consistent allocations to VB2?

Best regards,
Tomasz