Re: [PATCH v2 09/13] OMAPDSS: SDI: Create a function to set timings

[Archit Taneja <archit@ti.com>]

On Tuesday 14 August 2012 07:14 PM, Tomi Valkeinen wrote:
> On Thu, 2012-08-09 at 17:19 +0530, Archit Taneja wrote:
>> Create function omapdss_sdi_set_timings(). Configuring new timings is done the
>> same way as before, SDI is disabled, and re-enabled with the new timings in
>> dssdev. This just moves the code from the panel drivers to the SDI driver.
>>
>> The panel drivers shouldn't be aware of how SDI manages to configure a new set
>> of timings. This should be taken care of by the SDI driver itself.
>
> I'm not sure about this one. Although I see that dpi.c does currently
> the same thing as you're doing in your patch.

Even HDMI does the same thing.

>
> One thing is that we should try to remove dssdev uses from the output
> drivers, including use of dssdev->state.

Yes, we could do that by keeping a state of the output(and also checking 
state of the manager)

>
> The other thing is that I don't think the output driver should disable &
> enable the output during set timings. I think sdi's set_timings should
> return EBUSY if the output is enabled. The same way as other
> configuration functions should (like dpi_set_data_lines or such).
>
> I'm actually not sure if even the panel driver should disable & enable
> the output during set_timings. Perhaps it should be the caller's
> (omapdrm or such) responsibility....
>
> My reasoning here is that disabling & enabling the video output is not
> invisible to the upper layers, so doing it "in secret" may be bad.
>
> Then again, perhaps timings can be changed freely on some other
> platforms, and then it'd be nice if the panel driver wouldn't disable &
> enable the output.
>
> So I'm again not quite sure what's the best way to handle this... (of
> the dssdev->state I'm sure, its use should be removed from omapdss). Any
> thoughts?

I guess it depends on how drm/fb want to use it. I guess an output 
should have a set_timings() kind of op if it can do it seamlessly. I 
guess we can do that easily in DPI, for example, we could reduce the fps 
from 60 to 30 without causing an artefacts(I think). For outputs which 
can't do it, we could remove the set_timings totally.

However, it'll be kind of inconsistent for some outputs to set timings, 
and for others to not, and if in the future drm/fb gets exposed to ops 
too, we may have dirty checks to see if set_timings is populated or not.

The easiest way would be to make all set_timings just update the copy of 
the timings output has, and expect drm/fb to disable and re enable the 
panel. We may end up doing unnecessary gpio resets and configuration of 
the panels though.

Archit