On Wed, Jul 4, 2018 at 10:00 AM, Vinod vkoul@kernel.org wrote:
Hi Marek,
On 02-07-18, 15:08, Marek Szyprowski wrote:
'cmd_pause' DMA channel capability means that respective DMA engine supports both pausing and resuming given DMA channel. However, in some cases it is important to know if DMA channel can be paused without the need to resume it. This is a typical requirement for proper residue reading on transfer timeout in UART drivers. There are also some DMA engines with limited hardware, which doesn't really support resuming.
Am curious given that your hardware does not support resume, what was motivation for adding pause?
Reporting pause and resume capabilities separately allows UART drivers to properly check for the really required capabilities and operate in DMA mode also in systems with limited DMA hardware. On the other hand drivers, which rely on full channel suspend/resume support, should now check for both 'pause' and 'resume' features.
Existing clients of dma_get_slave_caps() have been checked and the only driver which rely on proper channel resuming is soc-generic-dmaengine-pcm driver, which has been updated to check the newly added capability. Existing 'cmd_pause' now only indicates that DMA engine support pausing given DMA channel.
The change looks fine to me. I was hoping that serial would also check this..
AFAIU serial does not need to resume.