On 2019-01-10 20:25, Boris Brezillon wrote:
On Thu, 10 Jan 2019 18:51:21 +0000 Peter Rosin peda@axentia.se wrote:
On 2019-01-10 18:29, Boris Brezillon wrote:
On Thu, 10 Jan 2019 15:10:48 +0000 Peter Rosin peda@axentia.se wrote:
The A2Q and UPDATE bits have no effect in the channel disable registers. However, since they are present, assume that the intention is to disable planes, not immediately as indicated by the RST bit, but on the next frame shift since that is what A2Q and UPDATE means in the channel enable registers.
Disabling the plane on the next frame shift is done with the EN bit, so use that.
It's been a long time, but I think I had a good reason for forcing a reset. IIRC, when you don't do that and the CRTC is disabled before the plane, the EN bit stays around, and next time you queue a plane update, you'll start with an invalid buf pointer.
It might be possible to clear the EN bit in ...CHDR before enabling the plane in ...CHER. Or is that too late?
I think I tried that, but I'm not sure (BTW, this change was done in bd4248bb5e8b ("drm: atmel-hlcdc: reset layer A2Q and UPDATE bits when
That patch is a big fat NOP if you read the documentation. Those bits are marked with a '-' for all LCDC channel disable registers, for all supported chips IIUC. Are the effects of those bits mentioned in any errata?
It would be good with a comment that the present undocumented disable method is intentional. That would have kept me from assuming the whole thing was just copy-paste junk from ..._enable that happened to work.
disabling it")). Anyway, I'm not even sure this is still needed now that atomic updates have a wait_for_flip_done/vblank() in the commit path.
The documentation for the RST bit states "Resets the layer immediately. The frame is aborted." which sounds a bit scary and heavy-handed. But again, I don't know what that actually means and what the effects are but that was the reason for me wanting to avoid the RST bit.
Cheers, Peter
But this patch is not overly important, I just wanted to avoid the resulting "black hole" when the plane DMA is disabled mid-frame. But disabling planes is probably not something that happens frequently and will perhaps not be noticed at all...
Okay. Other patches look good to me, I'm just waiting for Nicolas feedback before applying them.