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Date:   Tue, 4 Apr 2023 10:54:12 +0200
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Subject: Re: [PATCH v3 01/11] dmaengine: Add API function
 dmaengine_prep_slave_dma_array()
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To:     Paul Cercueil <paul@crapouillou.net>,
        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>,
        =?UTF-8?Q?Nuno_S=c3=a1?= <noname.nuno@gmail.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        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
References: <20230403154800.215924-1-paul@crapouillou.net>
 <20230404015944.502-1-hdanton@sina.com>
 <c9c9fa881aeda36862d0ad8c5a46472e0e363531.camel@crapouillou.net>
From:   =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>
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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@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 ;)

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@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);