Hi, On Fri, Dec 22, 2023 at 11:34 PM Doug Anderson <diand...@chromium.org> wrote: > > Hi, > > On Fri, Dec 22, 2023 at 2:29 AM Pin-yen Lin <treapk...@chromium.org> wrote: > > > > Hi Douglas, > > > > On Fri, Dec 22, 2023 at 5:56 AM Douglas Anderson <diand...@chromium.org> > > wrote: > > > > > > Unlike what is claimed in commit f5aa7d46b0ee ("drm/bridge: > > > parade-ps8640: Provide wait_hpd_asserted() in struct drm_dp_aux"), if > > > someone manually tries to do an AUX transfer (like via `i2cdump ${bus} > > > 0x50 i`) while the panel is off we don't just get a simple transfer > > > error. Instead, the whole ps8640 gets thrown for a loop and goes into > > > a bad state. > > > > > > Let's put the function to wait for the HPD (and the magical 50 ms > > > after first reset) back in when we're doing an AUX transfer. This > > > shouldn't actually make things much slower (assuming the panel is on) > > > because we should immediately poll and see the HPD high. Mostly this > > > is just an extra i2c transfer to the bridge. > > > > > > Fixes: f5aa7d46b0ee ("drm/bridge: parade-ps8640: Provide > > > wait_hpd_asserted() in struct drm_dp_aux") > > > Signed-off-by: Douglas Anderson <diand...@chromium.org> > > > --- > > > > > > drivers/gpu/drm/bridge/parade-ps8640.c | 5 +++++ > > > 1 file changed, 5 insertions(+) > > > > > > diff --git a/drivers/gpu/drm/bridge/parade-ps8640.c > > > b/drivers/gpu/drm/bridge/parade-ps8640.c > > > index 541e4f5afc4c..fb5e9ae9ad81 100644 > > > --- a/drivers/gpu/drm/bridge/parade-ps8640.c > > > +++ b/drivers/gpu/drm/bridge/parade-ps8640.c > > > @@ -346,6 +346,11 @@ static ssize_t ps8640_aux_transfer(struct drm_dp_aux > > > *aux, > > > int ret; > > > > > > pm_runtime_get_sync(dev); > > > + ret = _ps8640_wait_hpd_asserted(ps_bridge, 200 * 1000); > > > + if (ret) { > > > + pm_runtime_put_sync_suspend(dev); > > > + return ret; > > > + } > > > ret = ps8640_aux_transfer_msg(aux, msg); > > > pm_runtime_mark_last_busy(dev); > > > pm_runtime_put_autosuspend(dev); > > > -- > > > 2.43.0.472.g3155946c3a-goog > > > > > > > I think commit 9294914dd550 ("drm/bridge: parade-ps8640: Link device > > to ensure suspend/resume order") is trying to address the same > > problem, but we see this issue here because the device link is missing > > DL_FLAG_PM_RUNTIME. I prefer to add DL_FLAG_PM_RUNTIME here so we > > don't need to add a _ps8640_wait_hpd_asserted() after every > > pm_runtime_get_*() call. > > I disagree. We've had several discussions on the lists about this > topic before, though since I'm technically on vacation right now I'm > not going to go look them up. In general "pm_runtime" is not > sufficient for powering up DRM components. While DRM components can > use pm_runtime themselves (as we are doing here), powering up another > DRM component by grabbing a pm_runtime reference isn't right. There is > a reason for the complexity of the DRM prepare/enable and all the > current debates about the right order to call components in prepare() > just demonstrates further that a simple pm_runtime reference isn't > enough. > > It can be noted that, with ${SUBJECT} patch we _aren't_ powering up > the panel. I actually tested two cases on sc7180-lazor. In one case I > just closed the lid, which powered off the panel, but the touchscreen > kept the panel power rail on. In this case with my patch I could still > read the panel EDID. I then hacked the touchscreen off. Now when I > closed the lid I'd get a timeout. This is different than if we tried > to get a pm_runtime reference to the panel. > Okay, thanks for the detailed explanation. Then, let's go with the approach in this patch. So,
Tested-by: Pin-yen Lin <treapk...@chromium.org> Reviewed-by: Pin-yen Lin <treapk...@chromium.org> > > > As a side note, I've verified both this patch and DL_FLAG_PM_RUNTIME > > in our downstream v5.15 kernel and panel-edp driver. Both of them > > successfully wait for HPD asserted when the timeout used to happen, > > but the panel is black in that situation. That being said, this patch > > still brings us to a better state. Originally, panel_edp_resume() > > would return an error when the timeout occurs, so the panel-edp driver > > is stuck at an unexpected state. With this patch or > > DL_FLAG_PM_RUNTIME, the runtime PM callbacks won't fail and a system > > suspend/resume brings the panel back. > > OK. I'm going to shut off email for real this time while I enjoy some > time off. Hopefully the above convinces you. Otherwise I guess we can > continue to debate in mid-January. > > -Doug Happy holiday! Pin-yen