On Thu, Apr 23, 2020 at 6:26 PM Douglas Anderson dianders@chromium.org wrote:
People use panel-simple when they have panels that are builtin to their device. In these cases the HPD (Hot Plug Detect) signal isn't really used for hotplugging devices but instead is used for power sequencing. Panel timing diagrams (especially for eDP panels) usually have the HPD signal in them and it acts as an indicator that the panel is ready for us to talk to it.
Sometimes the HPD signal is hooked up to a normal GPIO on a system. In this case we need to poll it in the correct place to know that the panel is ready for us. In some system designs the right place for this is panel-simple.
When adding this support, we'll account for the case that there might be a circular dependency between panel-simple and the provider of the GPIO. The case this was designed for was for the "ti-sn65dsi86" bridge chip. If HPD is hooked up to one of the GPIOs provided by the bridge chip then in our probe function we'll always get back -EPROBE_DEFER. Let's handle this by allowing this GPIO to show up late if we saw -EPROBE_DEFER during probe. NOTE: since the gpio_get_optional() is used, if the "hpd-gpios" isn't there our variable will just be NULL and we won't do anything in prepare().
Signed-off-by: Douglas Anderson dianders@chromium.org Reviewed-by: Stephen Boyd swboyd@chromium.org
Changes in v3:
- Remind how gpio_get_optional() works in the commit message.
Reviewed-by: Linus Walleij linus.walleij@linaro.org
I have a small inkling to protest against calling this driver "panel-simple" as we tend to stockpile things like this.
I suppose panel-panacea.c is a better name at this point :/
Yours, Linus Walleij