Hi Maxime, On 23 September 2016 at 23:16, Maxime Ripard <maxime.ripard@xxxxxxxxxxxxxxxxxx> wrote: > On Thu, Sep 22, 2016 at 08:03:31AM +1000, Jonathan Liu wrote: >> Hi Maxime, >> >> On Thursday, 22 September 2016, Maxime Ripard <maxime.ripard@free-electrons. >> com> wrote: >> >> > On Wed, Sep 21, 2016 at 11:03:04PM +1000, Jonathan Liu wrote: >> > > The panel should be enabled after the controller so that the panel >> > > prepare/enable delays are properly taken into account. Similarly, the >> > > panel should be disabled before the controller so that the panel >> > > unprepare/disable delays are properly taken into account. >> > > >> > > This is useful for avoiding visual glitches. >> > >> > This is not really taking any delays into account, especially since >> > drm_panel_enable and prepare are suppose to block until their >> > operation is complete. >> >> >> drm_panel_prepare turns on power to the LCD using enable-gpios property of >> the panel and then blocks for prepare delay. The prepare delay for panel >> can be set to how long it takes between the time the panel is powered to >> when it is ready to receive images. If backlight property is specified the >> backlight will be off while the panel is powered on. >> >> drm_panel_enable blocks for enable delay and then turns on the backlight. >> The enable delay can be set to how long it takes for panel to start making >> the image visible after receiving the first valid frame. For example if the >> panel starts off as white and the TFT takes some time to initialize to >> black before it shows the image being received. >> >> Refer to drivers/gpu/drm/panel-panel.simple.c for details. > > From drm_panel.h: > > """ > * drm_panel_enable - enable a panel > * @panel: DRM panel > * > * Calling this function will cause the panel display drivers to be turned on > * and the backlight to be enabled. Content will be visible on screen after > * this call completes. > """ > > """ > * drm_panel_prepare - power on a panel > * @panel: DRM panel > * > * Calling this function will enable power and deassert any reset signals to > * the panel. After this has completed it is possible to communicate with any > * integrated circuitry via a command bus. > """ > > Those comments clearly says that the caller should not have to deal > with the delays, even more so by just moving calls around and hoping > that the code running in between is adding enough delay for the panel > to behave properly. > > Maxime > > -- > Maxime Ripard, Free Electrons > Embedded Linux and Kernel engineering > http://free-electrons.com https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/include/drm/drm_panel.h#n34 In comment for struct drm_panel_funcs: /** * struct drm_panel_funcs - perform operations on a given panel * @disable: disable panel (turn off back light, etc.) * @unprepare: turn off panel * @prepare: turn on panel and perform set up * @enable: enable panel (turn on back light, etc.) * @get_modes: add modes to the connector that the panel is attached to and * return the number of modes added * @get_timings: copy display timings into the provided array and return * the number of display timings available * * The .prepare() function is typically called before the display controller * starts to transmit video data. Panel drivers can use this to turn the panel * on and wait for it to become ready. If additional configuration is required * (via a control bus such as I2C, SPI or DSI for example) this is a good time * to do that. * * 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. Some panels require a certain amount of * time or frames before the image is displayed. This function is responsible * for taking this into account before enabling the backlight to avoid visual * glitches. * * Before stopping video transmission from the display controller it can be * necessary to turn off the panel to avoid visual glitches. This is done in * the .disable() function. Analogously to .enable() this typically involves * turning off the backlight and waiting for some time to make sure no image * is visible on the panel. It is then safe for the display controller to * cease transmission of video data. * * To save power when no video data is transmitted, a driver can power down * the panel. This is the job of the .unprepare() function. */ https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/gpu/drm/panel/panel-simple.c?id=refs/tags/v4.8-rc7#n39 In struct panel_desc: /** * @prepare: the time (in milliseconds) that it takes for the panel to * become ready and start receiving video data * @enable: the time (in milliseconds) that it takes for the panel to * display the first valid frame after starting to receive * video data * @disable: the time (in milliseconds) that it takes for the panel to * turn the display off (no content is visible) * @unprepare: the time (in milliseconds) that it takes for the panel * to power itself down completely */ Regards, Jonathan _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
