Hi, On Wed, Apr 12, 2023 at 9:19 PM Nikita Travkin <nikita@xxxxxxx> wrote: > > Doug Anderson писал(а) 13.04.2023 01:22: > > Hi, > > > > On Sat, Apr 8, 2023 at 1:20 AM Nikita Travkin <nikita@xxxxxxx> wrote: > >> > >> This bridge doesn't actually implement HPD due to it being way too slow > >> but instead expects the panel driver to wait enough to assume HPD is > >> asserted. However some panels (such as the generic 'edp-panel') expect > >> the bridge to deal with the delay and pass maximum delay to the aux > >> instead. > >> > >> In order to support such panels, add a dummy implementation of wait > >> that would just sleep the maximum delay and assume no failure has > >> happened. > >> > >> Signed-off-by: Nikita Travkin <nikita@xxxxxxx> > >> --- > >> This was suggested in [1] to make sure DT users can be semantically > >> correct (not adding no-hpd when the line is actually there) while > >> still using a hard delay to be faster than waiting the long debounce > >> time. > >> > >> [1] - https://lore.kernel.org/all/CAD=FV=VR7sKsquE25eF7joc7gPApu-vqwduZzjE=wFCoXjMYnQ@xxxxxxxxxxxxxx/ > >> --- > >> drivers/gpu/drm/bridge/ti-sn65dsi86.c | 19 +++++++++++++++++++ > >> 1 file changed, 19 insertions(+) > >> > >> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c > >> index 7a748785c545..260cad1fd1da 100644 > >> --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c > >> +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c > >> @@ -618,6 +618,24 @@ static ssize_t ti_sn_aux_transfer(struct drm_dp_aux *aux, > >> return len; > >> } > >> > >> +static int ti_sn_aux_wait_hpd_asserted(struct drm_dp_aux *aux, unsigned long wait_us) > >> +{ > >> + /* > >> + * The HPD in this chip is a bit useless (See comment in > >> + * ti_sn65dsi86_enable_comms) so if our driver is expected to wait > >> + * for HPD, we just assume it's asserted after the wait_us delay. > >> + * > >> + * In case we are asked to wait forever (wait_us=0) take conservative > >> + * 500ms delay. > >> + */ > >> + if (wait_us == 0) > >> + wait_us = 500000; > >> + > >> + usleep_range(wait_us, wait_us + 1000); > >> + > >> + return 0; > >> +} > >> + > >> static int ti_sn_aux_probe(struct auxiliary_device *adev, > >> const struct auxiliary_device_id *id) > >> { > >> @@ -627,6 +645,7 @@ static int ti_sn_aux_probe(struct auxiliary_device *adev, > >> pdata->aux.name = "ti-sn65dsi86-aux"; > >> pdata->aux.dev = &adev->dev; > >> pdata->aux.transfer = ti_sn_aux_transfer; > >> + pdata->aux.wait_hpd_asserted = ti_sn_aux_wait_hpd_asserted; > > > > This looks reasonable to me, but I think you only want this > > implementation if the "no-hpd" property _isn't_ present. In other > > words: > > > > if (!of_property_read_bool(np, "no-hpd")) > > pdata->aux.wait_hpd_asserted = ti_sn_aux_wait_hpd_asserted; > > > > Essentially: > > > > * If "no-hpd" is present in ti-sn65dsi86 then we'll assume that HPD is > > handled by the panel driver via a GPIO or a "no-hpd" there (which will > > cause the panel driver to wait the maximum duration). > > > > * If "no-hpd" isn't present in ti-sn65dsi86 then HPD is actually > > hooked up and thus the panel driver _won't_ handle it. > > > > Does that seem right? Presumably this should be explained by comments. > > > > This does sound reasonable indeed, I didn't think to add it > conditionally because, looking at the current users of > wait_hpd_asserted, they will first try the "no-hpd" paths > and will only call the bridge when they think it's on the > bridge to wait. > > Thus, if DT is modeled properly - Panel has no-hpd or a gpio, > wait_hpd_asserted will never be called anyway. Other bridges > seem to also unconditionally enable the method. > > For this to be a trouble, a panel driver has to be "broken" > with some form of calling wait_hpd_asserted despite knowing > the HPD line is not hooked up... > > So I feel like guarding the wait_hpd_asserted for no-hpd > users should not actually change much, but if you think > I should add the check anyway, please let me know. Ah, true, it shouldn't actually matter. I guess I still like it slightly better with the extra check but not enough that I'll insist on it. Thus: Reviewed-by: Douglas Anderson <dianders@xxxxxxxxxxxx> I can commit this to drm-misc-next, but I'll plan to wait ~1 week to see if anyone else has any comments about it. -Doug
