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

From: Paul Cercueil <paul@crapouillou.net>
To: Hillf Danton <hdanton@sina.com>
Cc: "Jonathan Cameron" <jic23@kernel.org>,
	"Lars-Peter Clausen" <lars@metafoo.de>,
	"Vinod Koul" <vkoul@kernel.org>,
	"Michael Hennerich" <Michael.Hennerich@analog.com>,
	"Nuno Sá" <noname.nuno@gmail.com>,
	"Sumit Semwal" <sumit.semwal@linaro.org>,
	"Christian König" <christian.koenig@amd.com>,
	linux-kernel@vger.kernel.org, dmaengine@vger.kernel.org,
	linux-iio@vger.kernel.org, linux-media@vger.kernel.org,
	dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org
Subject: Re: [PATCH v3 01/11] dmaengine: Add API function dmaengine_prep_slave_dma_array()
Date: Tue, 04 Apr 2023 09:42:11 +0200	[thread overview]
Message-ID: <c9c9fa881aeda36862d0ad8c5a46472e0e363531.camel@crapouillou.net> (raw)
In-Reply-To: <20230404015944.502-1-hdanton@sina.com>

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@crapouillou.net>
> > 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 ;)

Thanks for the feedback.

Cheers,
-Paul

> > 
> > Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> > 
> > ---
> > 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);