On 03/03/2015 01:30 PM, Mark Brown wrote:
On Tue, Mar 03, 2015 at 12:09:14PM +0200, Jyri Sarha wrote:
On 03/02/2015 09:58 PM, Lars-Peter Clausen wrote:
Can you include a description why this is needed and how and when it is
supposed to be used?
Would this addition do:
------------------------------------------------------------
These constraints help to disable the sample-format and sample-rate
combinations that do not properly work on a specific HW.
------------------------------------------------------------
Not entirely...
The reason why we need these is coming from limitations in McASP clock
generation. With a simple divider one can only produce certain bit-clocks.
With those bit-clocks we can only play/capture some sample-rate and
sample-width combinations accurately.
The McASP driver could try to set the constraints automatically. However,
since the constraint code can not select sample-width and sample-rate
combinations there is a compromise to be made between them. Making such
compromises automatically does not usually work that well.
...this is more the point. Perhaps the constraints language needs
improvement here?
Improving constraint functionality would certainly help, however the way
that code works is beyond my understanding and I do not believe such an
improvement would be coming from anybody else any time soon either.
In our case these properties could of course be added to McASP driver, but
then again I would expect that there is a wider need for this kind of
functionality. And it may not always be clear if either end of the link
alone is responsible for less than perfect operation.
The trouble with this sort of interface is that it's a quick and dirty
way for people to bodge around things rather than actually fixing them
properly. Of course sometimes fixing things properly is really hard and
that means we want a temporary bodge but having to put them in DT is
really unfortunate.
I agree with that. However, the simple-card binding goes already now
quite a bit beyond just describing the hardware. The binding for
instance decides the configuration that is going to be used over the
dai-link. These constraints could be seen as an extension to that
configuration.
I am wondering if there would be some better way to select the dai-link
configuration than writing it to DT or creating a custom machine driver
for each setup.
But about this patch. Should I just give it up, or would you be willing
to apply it if I improve the description more and add a warning against
using these properties to work around driver bugs to the binding document?
Best regards,
Jyri
--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
