On Tuesday 12 March 2013 07:59 PM, Tomi Valkeinen wrote:
On 2013-03-12 16:01, Archit Taneja wrote:
On Tuesday 12 March 2013 07:07 PM, Tomi Valkeinen wrote:
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.
Are you saying omapdrm picks the managers for the crtcs before knowing what panels there are? That can't work right... We need to know what outputs are to be used before we can select the managers. Or, we always need crtcs for all the managers.
That's how it is right now.
If we do know the panels, and thus outputs, then the managers to be used are found easily from output->dispc_channel.
Yes, my patch tries to do the same, but it could assign a manger which isn't the recommended channel. It can pick one from the list of supported channels. I've explained it a bit more below.
But, of course, the crtc to manager mapping could be changed (if omapdrm supports this). If omapdrm is asked to use only 1 crtc, but there are two panels, then only one panel can be used at a time, and the manager for the crtc needs to be changed when the panel to be used is changed. But even in this case used manager is clear, it comes from output->dispc_channel.
This is something I don't know that can be done or not, or if it can be done easily. A crtc isn't purely an overlay manager. It also needs to have one plane associated to it. So, if we want to change the overlay manager tied to a crtc on the fly, we should make sure that it's still connected to a plane pointing to the same buffer. This needs a better understanding of drm internals. I guess Rob could answer this better.
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.
I don't know, I feel like I'm not understanding something here =).
:)
I think what I said above is equivalent to what you said here:
"If we do know the panels, and thus outputs, then the managers to be used are found easily from output->dispc_channel."
Instead of using output->dispc_channel, the patch I made tried to get the first supported channel(in increasing order of channel index) for an output. If that channel was already taken/reserved by a previous output, it tries to take the next supported channel if there are enough crtcs left.
My patch would break things if it chooses a manager for an output for which we haven't written the necessary code yet(switching clock sources etc).
So, what I'm saying is that we should stick to output->dispc_channel. We iterate through all the panels, and by using output->dispc_channel, we get the manager for an output, and map that manager to a crtc, and make sure the number of unique managers we finally use is equal to NUM_CRTC.
Does that sound good?
Archit