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. Thanks for taking a look! Nikita > -Doug
