[Freedreno] [PATCH v1 2/2] drm/msm/dp: add mutex to protect internal_hpd against race condition between different threads

[Kuogee Hsieh]

internal_hpd is referenced at both plug and unplug handle.

The majority purpose of  mutext is try to serialize internal_hpd between 
dp_bridge_hpd_disable() and either plug or unplug handle.


On 5/10/2023 4:11 PM, Abhinav Kumar wrote:
>
>
> On 5/10/2023 3:46 PM, Stephen Boyd wrote:
>> Quoting Kuogee Hsieh (2023-05-10 13:31:05)
>>> Intrenal_hpd is referenced by event thread but set by drm bridge 
>>> callback
>>> context. Add mutex to protect internal_hpd to avoid conflicts between
>>> threads.
>>>
>>> Signed-off-by: Kuogee Hsieh <quic_khsieh at quicinc.com>
>>> ---
>>
>> This patch looks completely unnecessary. How can dp_bridge_hpd_enable()
>> be called at the same time that dp_bridge_hpd_disable() is called or
>> dp_bridge_hpd_notify() is called? Isn't there locking or ordering at a
>> higher layer?
>
> Ack. We can drop this patch because we are protected by 
> bridge->hpd_mutex in drm_bridge_hpd_enable() / drm_bridge_hpd_disable 
> () and drm_bridge_hpd_notify().