Re: [PATCH v3 01/11] dmaengine: Add API function dmaengine_prep_slave_dma_array()

[Christian König]

Am 04.04.23 um 09:42 schrieb Paul Cercueil:
> Hi Hillf,
>
> Le mardi 04 avril 2023 à 09:59 +0800, Hillf Danton a écrit :
> > On 3 Apr 2023 17:47:50 +0200 Paul Cercueil <paul@xxxxxxxxxxxxxxx>
> > > This function can be used to initiate a scatter-gather DMA transfer
> > > where the DMA addresses and lengths are located inside arrays.
> > >
> > > The major difference with dmaengine_prep_slave_sg() is that it
> > > supports
> > > specifying the lengths of each DMA transfer; as trying to override
> > > the
> > > length of the transfer with dmaengine_prep_slave_sg() is a very
> > > tedious
> > > process. The introduction of a new API function is also justified
> > > by the
> > > fact that scatterlists are on their way out.
> > Given sg's wayout and conceptually iovec and kvec (in
> > include/linux/uio.h),
> > what you add should have been dma_vec to ease people making use of
> > it.
> >
> >          struct dma_vec {
> >                  dma_addr_t      addr;
> >                  size_t          len;
> >          };
> Well it's not too late ;)

Yeah adding that is pretty much the job I have on my TODO list for quite 
some time.

I wouldn't mind if you start adding that and provide helper functions in 
DMA-buf to convert from/to an sg_table.

This way we can migrate the interface over to a new design over time.

Regards,
Christian.

> Thanks for the feedback.
>
> Cheers,
> -Paul
>
> > > Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
> > >
> > > ---
> > > v3: New patch
> > > ---
> > >   include/linux/dmaengine.h | 16 ++++++++++++++++
> > >   1 file changed, 16 insertions(+)
> > >
> > > diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> > > index c3656e590213..62efa28c009a 100644
> > > --- a/include/linux/dmaengine.h
> > > +++ b/include/linux/dmaengine.h
> > > @@ -912,6 +912,11 @@ struct dma_device {
> > >          struct dma_async_tx_descriptor
> > > *(*device_prep_dma_interrupt)(
> > >                  struct dma_chan *chan, unsigned long flags);
> > >   
> > > +       struct dma_async_tx_descriptor
> > > *(*device_prep_slave_dma_array)(
> > > +               struct dma_chan *chan, dma_addr_t *addrs,
> > > +               size_t *lengths, size_t nb,
> > > +               enum dma_transfer_direction direction,
> > > +               unsigned long flags);
> > Then the callback looks like
> >
> >          struct dma_async_tx_descriptor *(*device_prep_slave_vec)(
> >                  struct dma_chan *chan,
> >                  struct dma_vec *vec,
> >                  int nvec,
> >                  enum dma_transfer_direction direction,
> >                  unsigned long flags);