Re: drm/msm: Second DisplayPort regression in 6.8-rc1

[Johan Hovold <johan@kernel.org>]

On Mon, Feb 19, 2024 at 11:41:41AM +0100, Johan Hovold wrote:

> It seems my initial suspicion that at least some of these regressions
> were related to the runtime PM work was correct. The hard resets happens
> when the DP controller is runtime suspended after being probed:
 
> [   17.074925] bus: 'platform': __driver_probe_device: matched device aea0000.displayport-controller with driver msm-dp-display
> [   17.112000] msm-dp-display aea0000.displayport-controller: dp_display_probe - populate aux bus
> [   17.125208] msm-dp-display aea0000.displayport-controller: dp_pm_runtime_resume
> [   17.197909] msm-dp-display aea0000.displayport-controller: dp_pm_runtime_suspend
> [   17.198079] probe of aea0Format: Log Type - Time(microsec) - Message - Optional Info
> Log Type: B - Since Boot(Power On Reset),  D - Delta,  S - Statistic
> S - QC_IMAGE_VERSION_STRING=BOOT.MXF.1.1-00470-MAKENA-1
> S - IMAGE_VARIANT_STRING=SocMakenaWP
> S - OEM_IMAGE_VERSION_STRING=crm-ubuntu92
> 
>   < machine is reset by hypervisor >
> 
> Presumably the reset happens when controller is being shut down while
> still being used by the EFI framebuffer.
> 
> In the cases where the machines survives boot, the controller is never
> suspended.
> 
> When investigating this I've also seen intermittent:
> 
> 	[drm:dp_display_probe [msm]] *ERROR* device tree parsing failed

Note that there are further indications there may be more than one bug
here too.

I definitely see hard resets when dp_pm_runtime_suspend() is shutting
down the eDP PHY, but there are occasional resets also if I instrument
DP controller probe() to resume and then prevent the controller from
suspending until after a timeout (e.g. to be used as a temporary
workaround):

[   15.676495] bus: 'platform': __driver_probe_device: matched device aea0000.displayport-controller with driver msm-dp-display
[   15.769392] msm-dp-display aea0000.displayport-controller: dp_display_probe - populate aux bus
[   15.778808] msm-dp-display aea0000.displayport-controller: dp_display_probe - scheduling handover
[   15.789931] probe of aea0000.displayport-controller returned 0 after 91121 usecs
[   15.790460] bus: 'dp-aux': __driver_probe_device: matched device aux-aea0000.displayport-controller with driver panel-simple-dp-aux
Format: Log Type - Time(microsec) - Message - Optional Info
Log Type: B - Since Boot(Power On Reset),  D - Delta,  S - Statistic
S - QC_IMAGE_VERSION_STRING=BOOT.MXF.1.1-00470-MAKENA-1

I'll wait for the maintainers and authors of this code to comment, but
it seems the runtime PM work is broken in multiple ways.

Johan