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

On Tue, 2012-08-14 at 22:26 +0530, Archit Taneja wrote:

On Tuesday 14 August 2012 07:14 PM, Tomi Valkeinen wrote:

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 

Yes, that kind of thing is easy to do by just changing the pck divider,
which is in a shadow register. I mean, "easy" in theory, at least. Our
clock calculation doesn't work like that currently, though, so it could
end up changing DSS fck.

can't do it, we could remove the set_timings totally.

But we do need set_timings for other outputs also (like sdi). We just
can't change them just like that. Only outputs that do not need timings
are DSI command mode and rfbi.

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.

I think changing things like timings is quite a rare operation. The only
case it'd be necessary to change timings often, with speed, and without
artifacts would be the fps drop you mentioned, for lower power use with
panels that don't mind the fps drop.

If I understood correctly, Rob said that drm already disables the output
when changing the mode, when I asked if it's ok for the apply's
set_timings to require the output to be off.

In any case this is not a big issue, I mean, it's not causing any
problems. Somebody is going to disable the output anyway when changing
the timings. Perhaps even these patches are good, because they make the
set_timings consistent across the output drivers (don't they?).

 Tomi