Hi, On Tue, Apr 5, 2022 at 10:36 AM Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx> wrote: > > On 05/04/2022 20:02, Doug Anderson wrote: > > Hi, > > > > On Tue, Apr 5, 2022 at 5:54 AM Dmitry Baryshkov > > <dmitry.baryshkov@xxxxxxxxxx> wrote: > >>> 3. For DP and eDP HPD means something a little different. Essentially > >>> there are two concepts: a) is a display physically connected and b) is > >>> the display powered up and ready. For DP, the two are really tied > >>> together. From the kernel's point of view you never "power down" a DP > >>> display and you can't detect that it's physically connected until it's > >>> ready. Said another way, on you tie "is a display there" to the HPD > >>> line and the moment a display is there it's ready for you to do AUX > >>> transfers. For eDP, in the lowest power state of a display it _won't_ > >>> assert its "HPD" signal. However, it's still physically present. For > >>> eDP you simply have to _assume_ it's present without any actual proof > >>> since you can't get proof until you power it up. Thus for eDP, you > >>> report that the display is there as soon as we're asked. We can't > >>> _talk_ to the display yet, though. So in get_modes() we need to be > >>> able to power the display on enough to talk over the AUX channel to > >>> it. As part of this, we wait for the signal named "HPD" which really > >>> means "panel finished powering on" in this context. > >>> > >>> NOTE: for aux transfer, we don't have the _display_ pipe and clocks > >>> running. We only have enough stuff running to do the AUX transfer. > >>> We're not clocking out pixels. We haven't fully powered on the > >>> display. The AUX transfer is designed to be something that can be done > >>> early _before_ you turn on the display. > >>> > >>> > >>> OK, so basically that was a longwinded way of saying: yes, we could > >>> avoid the AUX transfer in probe, but we can't wait all the way to > >>> enable. We have to be able to transfer in get_modes(). If you think > >>> that's helpful I think it'd be a pretty easy patch to write even if it > >>> would look a tad bit awkward IMO. Let me know if you want me to post > >>> it up. > >> > >> I think it would be a good idea. At least it will allow us to judge, > >> which is the more correct way. > > > > I'm still happy to prototype this, but the more I think about it the > > more it feels like a workaround for the Qualcomm driver. The eDP panel > > driver is actually given a pointer to the AUX bus at probe time. It's > > really weird to say that we can't do a transfer on it yet... As you > > said, this is a little sideband bus. It should be able to be used > > without all the full blown infra of the rest of the driver. > > Yes, I have that feeling too. However I also have a feeling that just > powering up the PHY before the bus probe is ... a hack. There are no > obvious stopgaps for the driver not to power it down later. This is why I think we need to move to Runtime PM to manage this. Basically: 1. When an AUX transfer happens, you grab a PM runtime reference that _that_ powers up the PHY. 2. At the end of the AUX transfer function, you do a "put_autosuspend". Then it becomes not a hack, right? > A cleaner design might be to split all hotplug event handling from the > dp_display, provide a lightweight state machine for the eDP and select > which state machine to use depending on the hardware connector type. The > dp_display_bind/unbind would probably also be duplicated and receive > correct code flows for calling dp_parser_get_next_bridge, etc. > Basically that means that depending on the device data we'd use either > dp_display_comp_ops or (new) edp_comp_ops. > > WDYT? I don't think I know the structure of the MSM DP code to make a definitive answer here. I think I'd have to see a patch. However I'd agree in general terms that we need some different flows for the two. ;-) We definitely want to limit the differences but some of them will be unavoidable... -Doug
