On Fri, Jun 10, 2016 at 3:52 PM, Doug Anderson <dianders@xxxxxxxxxxxx> wrote: > Rob, > > On Fri, Jun 10, 2016 at 11:43 AM, Rob Clark <robdclark@xxxxxxxxx> wrote: >> On Fri, Jun 10, 2016 at 1:02 PM, Douglas Anderson <dianders@xxxxxxxxxxxx> wrote: >>> The Starry KR122EA0SRA is a 12.2", 1920x1200 TFT-LCD panel connected >>> using eDP interfaces. >> >> so drive-by comment... but shouldn't eDP be probe-able? Not sure why >> we need panel drivers or DT bindings? > > I was wondering about that too. As far as I can tell: > > 1. We need a panel driver because that appears to be what owns a > reference to the backlight / panel power regulator and that part is > not auto-probable. oh, hmm.. sad.. I was hoping that eDP would save us from dsi per-panel driver hell.. I guess being able to use panel-simple is at least an improvement. But panel specific sequences is sounds like panel-simple won't save us all the time :-( > 2. As far as I could tell, there is no way to declare a generic > (unspecified) panel in the device tree. Everyone seems to include > "simple-panel" in their compatible string but as far as I can tell > nothing in the kernel looks at it. > > 3. In theory, all the info specified here should match the EDID > exactly and thus (as you said) be probable. However, it sounds like > (for power sequencing reasons) there might be reasons why you'd want > to know exactly what panel was present beforehand. You might need to > power the panel and backlight in very specific sequences, for > instance. I'm not sure it's always 100% possible in all embedded > designs to read the EDID before you know how the sequencing should > work (but, of course, I'm a NOOB). > > 4. Reading the EDID can be slow. If you happen to know all the info > on the panel beforehand you can significantly speed up boot speed, > notably how fast you can get something on the screen. The theory is (although I think not true currently for most of the arm drivers) that we should be reading back from hw the current config from bootloader splash screen, to avoid a modeset (and conveniently also the need to read edid) at boot. BR, -R > > Anyway, maybe someone else who actually knows what they're talking > about will chime in. ;) > > -Doug -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
