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Message-ID: <599394c0220079b7b42dc732be817ca8a1eb4214.camel@crapouillou.net>
Date: Tue, 02 Apr 2024 13:31:25 +0200
From: Paul Cercueil <paul@...pouillou.net>
To: Vinod Koul <vkoul@...nel.org>
Cc: Jonathan Cameron <jic23@...nel.org>, Christian König
<christian.koenig@....com>, Jonathan Corbet <corbet@....net>, Lars-Peter
Clausen <lars@...afoo.de>, Sumit Semwal <sumit.semwal@...aro.org>, Nuno Sa
<nuno.sa@...log.com>, Michael Hennerich <michael.hennerich@...log.com>,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
dmaengine@...r.kernel.org, linux-iio@...r.kernel.org,
linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH v9 1/6] dmaengine: Add API function
dmaengine_prep_peripheral_dma_vec()
Hi Vinod,
Le jeudi 28 mars 2024 à 11:53 +0530, Vinod Koul a écrit :
> On 10-03-24, 13:48, Paul Cercueil wrote:
> > This function can be used to initiate a scatter-gather DMA
> > transfer,
> > where the address and size of each segment is located in one entry
> > of
> > the dma_vec array.
> >
> > 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.
> >
> > Note that dmaengine_prep_interleaved_dma() is not helpful either in
> > that
> > case, as it assumes that the address of each segment will be higher
> > than
> > the one of the previous segment, which we just cannot guarantee in
> > case
> > of a scatter-gather transfer.
> >
> > Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> > Signed-off-by: Nuno Sa <nuno.sa@...log.com>
> >
> > ---
> > v3: New patch
> >
> > v5: Replace with function dmaengine_prep_slave_dma_vec(), and
> > struct
> > 'dma_vec'.
> > Note that at some point we will need to support cyclic
> > transfers
> > using dmaengine_prep_slave_dma_vec(). Maybe with a new "flags"
> > parameter to the function?
> >
> > v7:
> > - Renamed *device_prep_slave_dma_vec() ->
> > device_prep_peripheral_dma_vec();
> > - Added a new flag parameter to the function as agreed between
> > Paul
> > and Vinod. I renamed the first parameter to prep_flags as it's
> > supposed to
> > be used (I think) with enum dma_ctrl_flags. I'm not really sure
> > how that API
> > can grow but I was thinking in just having a bool cyclic
> > parameter (as the
> > first intention of the flags is to support cyclic transfers)
> > but ended up
> > "respecting" the previously agreed approach.
> > ---
> > include/linux/dmaengine.h | 27 +++++++++++++++++++++++++++
> > 1 file changed, 27 insertions(+)
> >
> > diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> > index 752dbde4cec1..856df8cd9a4e 100644
> > --- a/include/linux/dmaengine.h
> > +++ b/include/linux/dmaengine.h
> > @@ -160,6 +160,16 @@ struct dma_interleaved_template {
> > struct data_chunk sgl[];
> > };
> >
> > +/**
> > + * struct dma_vec - DMA vector
> > + * @addr: Bus address of the start of the vector
> > + * @len: Length in bytes of the DMA vector
> > + */
> > +struct dma_vec {
> > + dma_addr_t addr;
> > + size_t len;
> > +};
> > +
> > /**
> > * enum dma_ctrl_flags - DMA flags to augment operation
> > preparation,
> > * control completion, and communicate status.
> > @@ -910,6 +920,10 @@ 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_peripheral_dma_vec)(
> > + struct dma_chan *chan, const struct dma_vec *vecs,
> > + size_t nents, enum dma_transfer_direction
> > direction,
> > + unsigned long prep_flags, unsigned long flags);
> > struct dma_async_tx_descriptor *(*device_prep_slave_sg)(
> > struct dma_chan *chan, struct scatterlist *sgl,
> > unsigned int sg_len, enum dma_transfer_direction
> > direction,
> > @@ -973,6 +987,19 @@ static inline struct dma_async_tx_descriptor
> > *dmaengine_prep_slave_single(
> > dir, flags,
> > NULL);
> > }
> >
> > +static inline struct dma_async_tx_descriptor
> > *dmaengine_prep_peripheral_dma_vec(
> > + struct dma_chan *chan, const struct dma_vec *vecs, size_t
> > nents,
> > + enum dma_transfer_direction dir, unsigned long prep_flags,
> > + unsigned long flags)
> > +{
> > + if (!chan || !chan->device || !chan->device-
> > >device_prep_peripheral_dma_vec)
> > + return NULL;
> > +
> > + return chan->device->device_prep_peripheral_dma_vec(chan,
> > vecs, nents,
> > + dir,
> > prep_flags,
> > +
> > flags);
> > +}
>
> API looks good to me, thanks
> Few nits though:
> - Can we add kernel-doc for this new API please
> - Also update the documentation adding this new api
> - Lastly, we seem to have two flags, I know you have added a comment
> but
> I dont seem to recall the discussion (looked at old threads for
> clue
> as well), can you please remind me why we need both? And in your
> case,
> what is the intended usage of these flags, i would prefer single
> clean one...
>
The "prep_flags" is a mask of "enum dma_ctrl_flags".
The second "flags" was supposed to be specific to this function, and
was to future-proof the API as we eventually want to have a "cyclic"
flag, which would emulate a cyclic transfer by linking the SG hardware
descriptors accordingly.
However - I think we can already do that with DMA_PREP_REPEAT and
DMA_PREP_LOAD_EOT, right? So we can probably drop the second "flags".
Cheers,
-Paul
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