Hi Tony,
Thank you for the patch.
On Wed, Apr 28, 2021 at 12:25:00PM +0300, Tony Lindgren wrote:
> On resume, dispc pm_runtime_force_resume() is not enabling the hardware
> as we pass the pm_runtime_need_not_resume() test as the device is suspended
> with no child devices.
>
> As the resume continues, omap_atomic_comit_tail() calls dispc_runtime_get()
> that calls rpm_resume() enabling the hardware, and increasing child_count
> for it's parent device.
>
> But at this point device_complete() has not yet been called for dispc. So
> when omap_atomic_comit_tail() calls dispc_runtime_put(), it won't idle
> the hardware as rpm_suspend() returns -EBUSY, and the clocks are left on
> after resume. The parent child count is not decremented as the -EBUSY
> cannot be easily handled until later on after device_complete().
>
> This can be easily seen for example after suspending Beagleboard-X15 with
> no displays connected, and by reading the CM_DSS_DSS_CLKCTRL register at
> 0x4a009120 after resume. After a suspend and resume cycle, it shows a
> value of 0x00040102 instead of 0x00070000 like it should.
>
> Let's fix the issue by calling dispc_runtime_suspend() and
> dispc_runtime_resume() directly from dispc_suspend() and dispc_resume().
> This leaves out the PM runtime related issues for system suspend.
>
> We could handle the issue by adding more calls to dispc_runtime_get()
> and dispc_runtime_put() from omap_drm_suspend() and omap_drm_resume()
> as suggested by Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>.
> But that would just add more inter-component calls and more dependencies
> to PM runtime for system suspend and does not make things easier in the
> long.
Based on my experience on the camera and display side with devices that
are made of multiple components, suspend and resume are best handled in
a controlled way by the top-level driver. Otherwise you end up having
different components suspending and resuming in random orders, and
that's a recipe for failure.
Can we get the omapdrm suspend/resume to run first/last, and
stop/restart the whole device from there ?
> See also earlier commit 88d26136a256 ("PM: Prevent runtime suspend during
> system resume") and commit ca8199f13498 ("drm/msm/dpu: ensure device
> suspend happens during PM sleep") for more information.
>
> Fixes: ecfdedd7da5d ("drm/omap: force runtime PM suspend on system suspend")
> Signed-off-by: Tony Lindgren <tony@xxxxxxxxxxx>
> ---
>
> Changes since v1:
> - Updated the description for a typo noticed by Tomi
> - Added more info about what all goes wrong
>
> ---
> drivers/gpu/drm/omapdrm/dss/dispc.c | 27 ++++++++++++++++++++++++++-
> 1 file changed, 26 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/omapdrm/dss/dispc.c b/drivers/gpu/drm/omapdrm/dss/dispc.c
> --- a/drivers/gpu/drm/omapdrm/dss/dispc.c
> +++ b/drivers/gpu/drm/omapdrm/dss/dispc.c
> @@ -182,6 +182,7 @@ struct dispc_device {
> const struct dispc_features *feat;
>
> bool is_enabled;
> + bool needs_resume;
>
> struct regmap *syscon_pol;
> u32 syscon_pol_offset;
> @@ -4887,10 +4888,34 @@ static int dispc_runtime_resume(struct device *dev)
> return 0;
> }
>
> +static int dispc_suspend(struct device *dev)
> +{
> + struct dispc_device *dispc = dev_get_drvdata(dev);
> +
> + if (!dispc->is_enabled)
> + return 0;
> +
> + dispc->needs_resume = true;
> +
> + return dispc_runtime_suspend(dev);
> +}
> +
> +static int dispc_resume(struct device *dev)
> +{
> + struct dispc_device *dispc = dev_get_drvdata(dev);
> +
> + if (!dispc->needs_resume)
> + return 0;
> +
> + dispc->needs_resume = false;
> +
> + return dispc_runtime_resume(dev);
> +}
> +
> static const struct dev_pm_ops dispc_pm_ops = {
> .runtime_suspend = dispc_runtime_suspend,
> .runtime_resume = dispc_runtime_resume,
> - SET_LATE_SYSTEM_SLEEP_PM_OPS(pm_runtime_force_suspend, pm_runtime_force_resume)
> + SET_LATE_SYSTEM_SLEEP_PM_OPS(dispc_suspend, dispc_resume)
> };
>
> struct platform_driver omap_dispchw_driver = {
--
Regards,
Laurent Pinchart
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