[alsa-devel] [PATCH v2 2/3] drm/mediatek: support HDMI jack status reporting

[CK Hu]

Hi, Tzung-Bi:

On Wed, 2020-02-12 at 19:31 +0800, Tzung-Bi Shih wrote:
> On Wed, Feb 12, 2020 at 4:19 PM CK Hu <ck.hu at mediatek.com> wrote:
> > I think hdmi_conn_detect() and mtk_hdmi_audio_hook_plugged_cb() would be
> > called in different thread. So it's necessary to use a mutex to protect
> > this.
> 
> Thanks for the reminder.  I feel using mutex here is overkill.  Please
> see https://patchwork.kernel.org/patch/11378413/ for my proposed
> solution.
> 

I'm not only consider the race condition of plugged_cb and codec_dev. I
also care about the atomic of mtk_cec_hpd_high() and hdmi->plugged_cb().
If these two function is not an atomic operation, below is an example of
problem:

<Status disconnected>
1. Thread A call mtk_hdmi_audio_hook_plugged_cb()
2. Thread A call mtk_cec_hpd_high() and get disconnected.
<Status connected>
3. Thread B call hdmi_conn_detect()
4. Thread B call mtk_cec_hpd_high() and get connected
5. Thread B callback plugged_cb() with connected
6. Thread A callback plugged_cb() with disconnected (Bug here)

Regards,
CK

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