On Tuesday 12 March 2013 07:07 PM, Tomi Valkeinen wrote:
On 2013-03-12 14:57, Archit Taneja wrote:
We could also use the recommended channel way for omapdrm, I can't
figure out what's the better approach at the moment.
Hmm, I think it'd be safer to use the recommended channel from omapdss
for now. The current omapdss code doesn't really let you use any other
channel than the recommended one (which was thus renamed to
dispc_channel in my later version).
I think omapdss needs to give the freedom to set a different dispc
manager for an output. This is because in omapdrm crtcs are sort of
floating, and when a connector(and it's encoder) needs to be enabled, it
tries to look search for a crtc it can connect to. If omapdss sort of
fixes the output->manager link, which is not how it should work.
I think it is fine for us to use this approach for omapfb when creating
the links, but not within dss.
For example, the code here:
- /*
- * XXX We shouldn't need dssdev->channel for this. The dsi pll clock
- * source for DPI is SoC integration detail, not something that should
- * be configured in the dssdev
- */
- dsidev = dpi_get_dsidev(dssdev->channel);
+ dsidev = dpi_get_dsidev(dpi.output.dispc_channel);
We are sort of using the recommended channel to figure out which DSI pll
to use. We don't have much of an option here because dpi_init_display()
happens much earlier. But if it were to connect to a different manager
later on, we would get into trouble.
Right. It should be changed to allow dynamic dispc channel changes (as I
said in my mail). But that requires changing how the output drivers and
the output.c work. Perhaps nothing too difficult, but just something
that has not been done =).
Or does your patch do a better job at selecting the outputs (I'm mostly
thinking about OMAP5 here, which has a bit more conflicts with the mgrs
and outputs than earlier omaps).
My approach is very drm oriented, the problem with omapdrm right now is
that we want to limit the number of crtcs(which map to managers). The
lesser the number of crtcs, the more free planes we have for overlaying.
If through bootargs or CONFIG, we set NUM_CRTCs to 2. We can only set up
only 2 overlay managers. My patch just tries to figure out which are the
best 2 managers to choose out of the total number of managers, in such a
way that most encoders/panels on the platform are supported.
The drm framework(I think) keeps the connections between crtc and
encoders flexible through the possible_crtcs flag maintained by
encoders. It figures out which crtc is free, and tries to use that one
at that moment. Once that encoder is done using it, the crtc can be used
by another encoder later. We can also change the crtc of an
encoder(after it's off).
So omapdss fixing the dispc channel for an output doesn't seem suitable
for drm.
So, I don't disagree with you. But I don't quite understand why we could
not use the fixed channels for now? They should work in all the boards
we have, right? Or is there something with DRM that forces the driver to
select the channel dynamically?
I think we can use fixed channels, but if the number of different fixed
channels crosses the number of crtcs the kernel wants, then we would
need to atleast change the channels of some of the outputs.
For example, suppose omapdrm is asked to use only 2 crtcs, and it picks
up LCD2 and TV managers. Now if there is some panel which says it's
recommended channel is LCD, then things won't work.
At the moment, omapdrm maps a crtc with a manger using a function called
pipe2chan() which just selects a manager with the biggest channel no. So
if the kernel is configured to have num_crtcs as 1. The single crtc will
be mapped to LCD2. This method is wrong, as it doesn't even look at the
type of panels at all. For an omap5 panda, the most suitable manager to
map to the crtc would be TV(for hdmi).
I think what we probably need to do is to combine both the methods. I.e,
make each output connectible to only one channel, and also iterate
through the panels in omapdrm to find the most suitable channels. So in
my patch, instead of looking at all the supported managers for an
output(checking with dss_feat_get_supported_outputs() on each manager),
I just look at the recommended channel, and try to map that manager.
This way, we have a better approach than the pipe2chan() thing, but we
restrict each encoder to connect to only one crtc, which we could extend
later if the need arises.
Should we go with this approach then?
As long as omapdss doesn't handle switching the clock sources (and
perhaps some other settings also, like OMAP5's DPI video source
selection. we've never had support for changing the channel later.),
having omapdrm select the channels could lead to problems if it happens
to select the wrong channel.
Yes, most of the other combinations wont work because of missing things
like clock source selection in DSS_CTRL and using the other video port
of DSI.
Archit
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