Hi, On Wed, Jun 23, 2021 at 4:26 PM Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: > > > > @@ -1365,7 +1384,8 @@ static int ti_sn_bridge_probe(struct i2c_client *client, > > > > > > pdata->bridge.funcs = &ti_sn_bridge_funcs; > > > pdata->bridge.of_node = client->dev.of_node; > > > - pdata->bridge.ops = DRM_BRIDGE_OP_EDID; > > > + pdata->bridge.ops = (pdata->no_hpd ? 0 : DRM_BRIDGE_OP_DETECT) > > > > Checking for "no_hpd" here is not the right test IIUC. You want to > > check for eDP vs. DP (AKA whether a panel is downstream of you or a > > connector). Specifically if downstream of you is a panel then (I > > believe) HPD won't assert until you turn on the panel and you won't > > turn on the panel (which happens in pre_enable, right?) until HPD > > fires, so you've got a chicken-and-egg problem. If downstream of you > > is a connector, though, then by definition HPD has to just work > > without pre_enable running so then you're OK. > > Agreed. It's even more true now that your rework has landed, as in the > eDP case EDID is handled by the panel driver. I'll rework this. > > Should I also condition setting HPD_DISABLE to the presence of a panel > then ? I could drop of_property_read_bool() and set > > pdata->no_hpd = !!panel; > > > I guess then you'd need to figure out what to do if someone wants to > > use "HPD" on eDP. Do you need to put a polling loop in pre_enable > > then? Or you could just punt not support this case until someone needs > > it. > > I think I'll stop short of saving the world this time, yes :-) We'll see > what to do when this case arises. How about as a compromise you still call of_property_read_bool() but add some type of warning in the logs if someone didn't set "no-hpd" but they have a panel? > > > + | DRM_BRIDGE_OP_EDID; > > > > IMO somewhere in here if HPD is being used like this you should throw > > in a call to pm_runtime_get_sync(). I guess in your solution the > > regulators (for the bridge, not the panel) and enable pin are just > > left on all the time, > > Correct, on my development board the SN65DSI86 is on all the time, I > can't control that. > > > but plausibly someone might want to build a > > system to use HPD and also have the enable pin and/or regulators > > controlled by this driver, right? > > True. DRM doesn't make this very easy, as, as far as I can tell, there's > no standard infrastructure for userspace to register an interest in HPD > that could be notified to bridges. I think it should be fixable, but > it's out of scope for this series :-) Should I still add a > pm_runtime_get_sync() at probe time, or leave this to be addressed by > someone who will need to implement power control ? IMO if you've detected you're running in DP mode you should add the pm_runtime_get_sync() in probe to keep it powered all the time and that seems the simplest. Technically I guess that's not really required since you're polling and you could power off between polls, but then you'd have to re-init a bunch of your state each time you polled too. If you ever transitioned to using an IRQ for HPD then you'd have to keep it always powered anyway. -Doug
