Re: [PATCH v1 3/3] dma: tegra: avoid int overflow for transferred count

Lars-Peter Clausen
2014-05-07T19:15:56Z

On 05/07/2014 06:38 PM, Stephen Warren wrote:
> On 05/06/2014 03:22 PM, Christopher Freeman wrote:
>> bytes_transferred will overflow during long audio playbacks. Since
>> the driver only ever consults this value modulo bytes_requested, store the
>> value modulo bytes_requested.
>
> The audio driver may only interpret the value modulo bytes_requested,
> but what about other drivers such as the high-speed UART (and SPI?) drivers?
>
> What is the dmaengine API's design requirement here, and what do other
> dmaengine drivers do. If it's to store the modulo, then I'm fine with
> this change.

Yep, this part of the API. The residue should be between transfer length and
0. While 0 is special and should only be returned if the transfer has
finished. For cyclic transfers this means it should never be zero. So if
transferred_bytes is incremented modulo length and residue is length -
transferred_bytes you get the correct result.