On Fri, Nov 08, 2019 at 03:12:28PM -0700, Jeffrey Hugo wrote: > On Fri, Nov 8, 2019 at 2:29 PM Stephan Gerhold <stephan@xxxxxxxxxxx> wrote: > > > > At the moment, the MSM DSI driver calls drm_panel_enable() rather early > > from the DSI bridge pre_enable() function. At this point, the encoder > > (e.g. MDP5) is not enabled, so we have not started transmitting > > video data. > > > > However, the drm_panel_funcs documentation states that enable() > > should be called on the panel *after* video data is being transmitted: > > > > The .prepare() function is typically called before the display controller > > starts to transmit video data. [...] After the display controller has > > started transmitting video data, it's safe to call the .enable() function. > > This will typically enable the backlight to make the image on screen visible. > > > > Calling drm_panel_enable() too early causes problems for some panels: > > The TFT LCD panel used in the Samsung Galaxy Tab A 9.7 (2015) (APQ8016) > > uses the MIPI_DCS_SET_DISPLAY_BRIGHTNESS command to control > > backlight/brightness of the screen. The enable sequence is therefore: > > > > drm_panel_enable() > > drm_panel_funcs.enable(): > > backlight_enable() > > backlight_ops.update_status(): > > mipi_dsi_dcs_set_display_brightness(dsi, bl->props.brightness); > > > > The panel seems to silently ignore the MIPI_DCS_SET_DISPLAY_BRIGHTNESS > > command if it is sent too early. This prevents setting the initial brightness, > > causing the display to be enabled with minimum brightness instead. > > Adding various delays in the panel initialization code does not result > > in any difference. > > > > On the other hand, moving drm_panel_enable() to dsi_mgr_bridge_enable() > > fixes the problem, indicating that the panel requires the video stream > > to be active before the brightness command is accepted. > > > > Therefore: Move drm_panel_enable() to dsi_mgr_bridge_enable() to > > delay calling it until video data is being transmitted. > > > > Move drm_panel_disable() to dsi_mgr_bridge_disable() for similar reasons. > > (This is not strictly required for the panel affected above...) > > > > Tested-by: Jasper Korten <jja2000@xxxxxxxxx> > > Signed-off-by: Stephan Gerhold <stephan@xxxxxxxxxxx> > > --- > > Since this is a core change I thought it would be better to send this > > early. I believe Jasper still wants to finish some other changes before > > submitting the initial device tree for the Samsung Galaxy Tab A 9.7 (2015). ;) > > > > I also tested it on msm8916-samsung-a5u-eur, its display is working fine > > with or without this patch. > > Nack, please. I was curious so I threw this on the Lenovo Miix 630 > laptop. I don't get a display back with this patch. I'll try to > figure out why, but currently I can't get into the machine. Thanks for testing the patch! Let's try to figure that out... I'm a bit confused, but this might be because I'm not very familiar with the MSM8998 laptops. It does not seem to have display in mainline yet, so do you have a link to all the patches you are using at the moment? Judging from the patches I was able to find, the Lenovo Miix 630 is using a DSI to eDP bridge. Isn't the panel managed by the bridge driver in that case? struct msm_dsi contains: /* * panel/external_bridge connected to dsi bridge output, only one of the * two can be valid at a time */ struct drm_panel *panel; struct drm_bridge *external_bridge; So if you have "external_bridge" set in your case, "panel" should be NULL. I have only moved code that uses msm_dsi->panel, so my patch really shouldn't make any difference for you. Am I confusing something here? Thanks, Stephan
