Hi Maxime,

On Thursday 23 October 2014 15:19:33 Maxime Ripard wrote:

On Thu, Oct 23, 2014 at 12:21:31AM +0300, Laurent Pinchart wrote:

quoted

Hi Maxime,

Thank you for the patch.

On Wednesday 22 October 2014 17:44:12 Maxime Ripard wrote:

quoted

For the slave caps retrieval to be really useful, most drivers need to
implement it.

Hence, we need to be slightly more aggressive, and trigger a warning at
registration time for drivers that don't fill their caps infos in order
to
encourage them to implement it.

Signed-off-by: Maxime Ripard <redacted>
---

 drivers/dma/dmaengine.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 98e9431f85ec..4e18981b16bd 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c

@@ -827,6 +827,9 @@ int dma_async_device_register(struct dma_device

*device) BUG_ON(!device->device_issue_pending);

 	BUG_ON(!device->dev);

+	WARN(dma_has_cap(DMA_SLAVE, device->cap_mask) &&
!device->generic_slave_caps,
+	     "this driver doesn't support generic slave capabilities
reporting\n");
+

This might be slightly too aggressive.

I disagree with that. If we want at some point to have the drivers
implement it, we should be aggressive (and note that we don't break
anything, the driver will still work as it used to).

I meant too aggressive given the possibility that a driver might need its own 
implementation if not all channels have the same capability.

quoted

I agree with your previous comment on all DMA engine drivers
returning the same capabilities for all channels, but it might not
be true anymore in the future, in which case drivers will need to
implement a custom slave caps function. We could delay support for
that to when it's needed though.

Actually, my next patch (59) is removing such possibility... And you
acked it ;)

Is it still something we should be concerned about?

Maybe not now, we can always add that possibility back in the future if 
needed.

-- 
Regards,

Laurent Pinchart