Lars-Peter Clausen <lars@xxxxxxxxxx> writes:
> On 07/16/2015 03:08 PM, Vinod Koul wrote:
>> On Mon, Jul 13, 2015 at 01:00:54PM +0200, Lars-Peter Clausen wrote:
>>>>>> Actually there has never been a recommendation for slave cases. It came from async
>>>>>> API and slave users should never have used it, untill now.
>>>>>
>>>>> That doesn't reflect reality. The fast majority slave API users set
>>>>> the flag and some DMAengine drivers expect it to be set.
>>>> That is simply wrong and we need to fix that
>>>
>>> Could you explain why you think that it is wrong?
>>>
>>> I think we might have different understandings of what exactly the
>>> DMA_CTRL_ACK flag means.
>> This is documented now
>>
>> * DMA_CTRL_ACK
>> - If set, the transfer can be reused after being completed.
>> - There is a guarantee the transfer won't be freed until it is acked
>> by async_tx_ack().
>> - As a consequence, if a device driver wants to skip the dma_map_sg()
>> and
>> dma_unmap_sg() in between 2 transfers, because the DMA'd data wasn't used,
>> it can resubmit the transfer right after its completion.
>>
>> Any user who doesnt want this interpretation should be fixed, any driver not
>> doing this should be fixed :)
>
> That would be every user and every driver. This documentation was added as part
> of Robert's series, but does not agree, with either other documentation of the
> flag, e.g. in include/linux/dmaengine.h, nor with any of the users. The
> documentation needs to be fixed, not the other way around.
Might it be possible that I implemented code and documentation with the inverted
logic ? Or said differently, if I had written :
- If *clear*, the transfer can be reused after being completed.
And inverted the test in virt-dma.c, would it be better, Vinod ?
I'm asking because in the code I read :
- include/linux/dmaengine.h:
if clear, the descriptor cannot be reused until the client
acknowledges receipt.
- drivers/dma/virt-dma.c
If set, the transfer can be reused after being completed.
If I invert my DMA_CTRL_ACK documentation and code logic in virt-dma.c, would
that fit the old meaning, and would that still be acceptable by Vinod ?
Cheers.
--
Robert
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