On Tue, Mar 16, 2021 at 02:08:19PM -0700, Douglas Anderson wrote: > The sc7180-trogdor-pompom board might be attached to any number of a > pile of eDP panels. At the moment I'm told that the list might include: > - KD KD116N21-30NV-A010 > - KD KD116N09-30NH-A016 > - Starry 2081116HHD028001-51D > - Sharp LQ116M1JW10 > > It should be noted that while the EDID programmed in the first 3 > panels indicates that they should run with exactly the same timing (to > keep things simple), the 4th panel not only needs different timing but > has a different resolution. > > As is true in general with eDP panels, we can figure out which panel > we have and all the info needed to drive its pixel clock by reading > the EDID. However, we can do this only after we've powered the panel > on. Powering on the panels requires following the timing diagram in > each panel's datasheet which specifies delays between certain > actions. This means that, while we can be quite dynamic about handling > things we can't just totally skip out on describing the panel like we > could do if it was connected to an external-facing DP port. > > While the different panels have slightly different delays, it's > possible to come up with a set of unified delays that will work on all > the panels. From reading the datasheets: > * KD KD116N21-30NV-A010 and KD KD116N09-30NH-A016 > - HPD absent delay: 200 ms > - Unprepare delay: 150 ms (datasheet is confusing, might be 500 ms) > * Starry 2081116HHD028001-51D > - HPD absent delay: 100 ms > - Enable delay: (link training done till enable BL): 200 ms > - Unprepare delay: 500 ms > * Sharp LQ116M1JW10 > - HPD absent delay: 200 ms > - Unprepare delay: 500 ms > - Prepare to enable delay (power on till backlight): 100 ms > > Unified: > - HPD absent delay: 200 ms > - Unprepare delay: 500 ms > - Enable delay: 200 ms > > NOTE: in theory the only thing that we _really_ need unity on is the > "HPD absent delay" since once the panel asserts HPD we can read the > EDID and could make per-panel decisions if we wanted. > > Let's create a definition of "a panel that can be attached to pompom" > as a panel that provides a valid EDID and can work with the standard > pompom power sequencing. If more panels are later attached to pompom > then it's fine as long as they work in a compatible way. > > One might ask why we can't just use a generic string here and provide > the timings directly in the device tree file. As I understand it, > trying to describe generic power sequencing in the device tree is > frowned upon and the one instance (SD/MMC) is regarded as a mistake > that shouldn't be repeated. Specifying a power sequence per board (or > per board class) feels like a reasonable compromise. We're not trying > to define fully generic power sequence bindings but we can also take > advantage of the semi-probable properties of the attached device. > > NOTE: I believe that past instances of supporting this type of thing > have used the "white lie" approach. One representative panel was > listed in the device tree. The power sequencings of this > representative panel were OK to use across all panels that might be > attached and other differences were handled by EDID. This patch > attempts to set a new precedent and avoid the need for the white lie. > > Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx> > --- Sounds reasonable to me if DT maintainers can live with this abstract hardware definition. It's clearer than the 'white lie' approach. It's then up to the vendor/manufacturer to ensure to only ship devices with panels that have compatible timings. > .../devicetree/bindings/display/panel/panel-simple.yaml | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/Documentation/devicetree/bindings/display/panel/panel-simple.yaml b/Documentation/devicetree/bindings/display/panel/panel-simple.yaml > index 62b0d54d87b7..9807dbc1cceb 100644 > --- a/Documentation/devicetree/bindings/display/panel/panel-simple.yaml > +++ b/Documentation/devicetree/bindings/display/panel/panel-simple.yaml > @@ -140,6 +140,10 @@ properties: > - giantplus,gpg48273qs5 > # GiantPlus GPM940B0 3.0" QVGA TFT LCD panel > - giantplus,gpm940b0 > + # A panel connected to a google,pompom board. Panel is guaranteed to > + # confirm to google,pompom-panel power sequencing requirements and then s/confirm/conform/ ? > + # the specific panel will be probed via EDID. > + - google,pompom-panel > # HannStar Display Corp. HSD070PWW1 7.0" WXGA TFT LCD panel > - hannstar,hsd070pww1 > # HannStar Display Corp. HSD100PXN1 10.1" XGA LVDS panel FWIW: Reviewed-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
