On Mon, Mar 02, 2020 at 10:53:56PM +0000, Peter Rosin wrote: > On 2020-03-02 21:34, Ville Syrjala wrote: > > From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > > > > The currently listed dotclock disagrees with the currently > > listed vrefresh rate. Change the dotclock to match the vrefresh. > > > > Someone tell me which (if either) of the dotclock or vreresh is > > correct? > > TL/DR; I do not care if you change the refresh rate or the dotclock. > > The whole entry for that panel in simple-panel is dubious. The panel > is really an LVDS panel (capable of both VESA/Jeida RGB888, selectable > with the SELLVDS pin). With Jeida you can, as usual, omit the 4th > data channel and use the panel with RGB666. In either case, you need > an LVDS signal and nothing else... > > The panel can also rotate the picture 180 degrees using the RL/UD pin. > > These options are of course not expressed in the simple panel driver > (and we have always used fixed signals for those pins in our designs, > IIRC). As far as I'm concerned, the panel can be removed from > simple-panel. Our device trees are nowadays correctly expressing the > hardware with an LVDS encoder between the RGB output and the panel > and points to the panel-lvds driver for the panel. How do you make sure that you always bind against the correct driver? If it matches simple-panel and panel-lvds, it's not deterministically going to pick the right one. Well, it may actually be deterministic on Linux, but perhaps only by accident. > The reason that it is as it is, is that we obviously didn't understand > what we were doing when we added the entry, and this garbage was what > we came up with that produced a picture. > > If you want to keep the panel in simple-panel despite all this, the > timing constraints are as follows: > > Pixel clock 50-80 MHz, 65 MHz typical > Horizontal period 1094-1720 clocks, 1344 typical > 16.0-23.4 us 20.7 us > Horizontal enable 1024 clocks, always > Vertical period 776-990 lines, 806 typical > 13.3-18.0 ms 16.7 ms > Vertical enable 768 lines, always > > Using a "long" (the datasheet is not very specific on this issue) vertical > period may introduce deterioration of display quality, flicker etc. > > I don't think the division between front-porch/back-porch matters much. > > That said, I have no idea whatsoever if others have started using this > panel entry. My guess is that it has zero users, but who can tell? A quick grep shows that arch/arm/boot/dts/at91-nattis-2-natte-2.dts is the only device tree that uses this panel in the upstream kernel. Thierry
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