On Fri, Mar 26, 2021 at 5:38 AM Thierry Reding <thierry.reding@xxxxxxxxx> wrote: > > On Wed, Mar 17, 2021 at 06:53:04PM -0700, Rob Clark wrote: > > On Wed, Mar 17, 2021 at 4:27 PM Matthias Kaehlcke <mka@xxxxxxxxxxxx> wrote: > > > > > > 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. > > > > Yeah, it is a weird grey area between "discoverable" and "not > > discoverable".. but I favor DT reflecting reality as much as > > possible/feasible, so I think this is definity cleaner than "white > > lies" > > This is practically no different than the "white lie". I suppose you > could perhaps call it "more honest", if you want. > > The point remains that unless we describe exactly which panel we're > dealing with, we ultimately have no way of properly quirking anything if > we ever have to. Also, once we allow this kind of wildcard we can > suddenly get into a situation where people might want to reuse this on > something that's not at all a google-pompom board because the same > particular power sequence happens to work on on some other board. > > Similarly I can imagine a situation where we could now have the same > panel supported by multiple different wildcard compatible strings. How > is that supposed to be any cleaner than what we have now? > > And I still keep wondering why bootloaders can't be taught about these > kinds of things. We have in the past discussed various solutions where > the bootloader could detect the type of panel connected and set the > proper compatible string. The bootloader cannot detect the panel without powering up the panel, which it normally does not do if you are not in dev-mode (it would add a significant amount of time to bootup, which is why we can't do this) BR, -R > If that's too complicated and these really are standardized interfaces > that work across a wide range of devices with perhaps a couple of > standard parameter, then introducing a standard connector type like > Rob Herring is suggesting makes more sense because that more properly > describes where exactly the standardization is going on (i.e. at the > interface level rather than the panel level). > > Thierry
