Re: [PATCH v1] drm/bridge: cdns-dsi: Replace deprecated UNIVERSAL_DEV_PM_OPS()

[Vitor Soares <ivitro@gmail.com>]

On Tue, 2025-04-29 at 09:32 +0300, Tomi Valkeinen wrote:
> Hi,
> 
> On 28/04/2025 12:40, Vitor Soares wrote:
> > From: Vitor Soares <vitor.soares@toradex.com>
> > 
> > The deprecated UNIVERSAL_DEV_PM_OPS() macro uses the provided callbacks
> > for both runtime PM and system sleep. This causes the DSI clocks to be
> > disabled twice: once during runtime suspend and again during system
> > suspend, resulting in a WARN message from the clock framework when
> > attempting to disable already-disabled clocks.
> > 
> > [   84.384540] clk:231:5 already disabled
> > [   84.388314] WARNING: CPU: 2 PID: 531 at /drivers/clk/clk.c:1181
> > clk_core_disable+0xa4/0xac
> > ...
> > [   84.579183] Call trace:
> > [   84.581624]  clk_core_disable+0xa4/0xac
> > [   84.585457]  clk_disable+0x30/0x4c
> > [   84.588857]  cdns_dsi_suspend+0x20/0x58 [cdns_dsi]
> > [   84.593651]  pm_generic_suspend+0x2c/0x44
> > [   84.597661]  ti_sci_pd_suspend+0xbc/0x15c
> > [   84.601670]  dpm_run_callback+0x8c/0x14c
> > [   84.605588]  __device_suspend+0x1a0/0x56c
> > [   84.609594]  dpm_suspend+0x17c/0x21c
> > [   84.613165]  dpm_suspend_start+0xa0/0xa8
> > [   84.617083]  suspend_devices_and_enter+0x12c/0x634
> > [   84.621872]  pm_suspend+0x1fc/0x368
> > 
> > To address this issue, replace UNIVERSAL_DEV_PM_OPS() with
> > DEFINE_RUNTIME_DEV_PM_OPS(), which avoids redundant suspend/resume calls
> > by checking if the device is already runtime suspended.
> > 
> > Cc: <stable@vger.kernel.org> # 6.1.x
> > Fixes: e19233955d9e ("drm/bridge: Add Cadence DSI driver")
> > Signed-off-by: Vitor Soares <vitor.soares@toradex.com>
> > ---
> >   drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c | 10 +++++-----
> >   1 file changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
> > b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
> > index b022dd6e6b6e..62179e55e032 100644
> > --- a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
> > +++ b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
> > @@ -1258,7 +1258,7 @@ static const struct mipi_dsi_host_ops cdns_dsi_ops = {
> >         .transfer = cdns_dsi_transfer,
> >   };
> >   
> > -static int __maybe_unused cdns_dsi_resume(struct device *dev)
> > +static int cdns_dsi_resume(struct device *dev)
> >   {
> >         struct cdns_dsi *dsi = dev_get_drvdata(dev);
> >   
> > @@ -1269,7 +1269,7 @@ static int __maybe_unused cdns_dsi_resume(struct
> > device *dev)
> >         return 0;
> >   }
> >   
> > -static int __maybe_unused cdns_dsi_suspend(struct device *dev)
> > +static int cdns_dsi_suspend(struct device *dev)
> >   {
> >         struct cdns_dsi *dsi = dev_get_drvdata(dev);
> >   
> > @@ -1279,8 +1279,8 @@ static int __maybe_unused cdns_dsi_suspend(struct
> > device *dev)
> >         return 0;
> >   }
> >   
> > -static UNIVERSAL_DEV_PM_OPS(cdns_dsi_pm_ops, cdns_dsi_suspend,
> > cdns_dsi_resume,
> > -                           NULL);
> > +static DEFINE_RUNTIME_DEV_PM_OPS(cdns_dsi_pm_ops, cdns_dsi_suspend,
> > +                                cdns_dsi_resume, NULL);
> 
> I'm not sure if this, or the UNIVERSAL_DEV_PM_OPS, is right here. When 
> the system is suspended, the bridge drivers will get a call to the 
> *_disable() hook, which then disables the device. If the bridge driver 
> would additionally do something in its system suspend hook, it would 
> conflict with normal disable path.
> 
> I think bridges/panels should only deal with runtime PM.
> 
>   Tomi
> 

In the proposed change, we make use of pm_runtime_force_suspend() during
system-wide suspend. If the device is already suspended, this call is a
no-op and disables runtime PM to prevent spurious wakeups during the
suspend period. Otherwise, it triggers the device’s runtime_suspend()
callback.

I briefly reviewed other bridge drivers, and those that implement runtime
PM appear to follow a similar approach, relying solely on runtime PM
callbacks and using pm_runtime_force_suspend()/resume() to handle
system-wide transitions.

Best regards,
Vitor Soares