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

[Tomi Valkeinen]

Hi,

On 05/05/2025 17:45, Vitor Soares wrote:
> 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 at 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 at vger.kernel.org> # 6.1.x
>>> Fixes: e19233955d9e ("drm/bridge: Add Cadence DSI driver")
>>> Signed-off-by: Vitor Soares <vitor.soares at 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.

Yes, I see such a solution in some of the bridge and panel drivers. I'm 
probably missing something here, as I don't think it's correct.

Why do we need to set the system suspend/resume hooks? What is the 
scenario where those will be called, and the 
pm_runtime_force_suspend()/resume() do something that's not already done 
via the normal DRM pipeline enable/disable?

  Tomi