hdmi_conn_detect and mtk_hdmi_audio_hook_plugged_cb woule be called
by different threads. plugged_cb and codec_dev are in danger of race
condition.
Fixes by:
- Checks NULLs first.
- Uses WRITE_ONCE() to prevent store tearing (i.e. write to plugged_cb
after codec_dev).
- Uses codec_dev as a signal to report HDMI jack status.
The patch intends to not use mutex to protect the shared variables.
In runtime, mtk_hdmi_audio_hook_plugged_cb would be called only once
if no one rebinds the sound card. In contrast, hdmi_conn_detect could
be called multiple times. Uses a mutex within hdmi_conn_detect calling
path is a waste (no lock contention).
Fixes: 5d3c64477392 ("drm/mediatek: support HDMI jack status reporting")
Signed-off-by: Tzung-Bi Shih <tzungbi@xxxxxxxxxx>
---
drivers/gpu/drm/mediatek/mtk_hdmi.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/mediatek/mtk_hdmi.c b/drivers/gpu/drm/mediatek/mtk_hdmi.c
index 03aeb73005ef..746567c91bb7 100644
--- a/drivers/gpu/drm/mediatek/mtk_hdmi.c
+++ b/drivers/gpu/drm/mediatek/mtk_hdmi.c
@@ -1201,7 +1201,7 @@ mtk_hdmi_update_plugged_status(struct mtk_hdmi *hdmi)
{
bool connected = mtk_cec_hpd_high(hdmi->cec_dev);
- if (hdmi->plugged_cb && hdmi->codec_dev)
+ if (hdmi->codec_dev)
hdmi->plugged_cb(hdmi->codec_dev, connected);
return connected ?
@@ -1669,8 +1669,12 @@ static int mtk_hdmi_audio_hook_plugged_cb(struct device *dev, void *data,
{
struct mtk_hdmi *hdmi = data;
- hdmi->plugged_cb = fn;
- hdmi->codec_dev = codec_dev;
+ if (!fn || !codec_dev)
+ return -EINVAL;
+
+ /* Use WRITE_ONCE() to prevent store tearing. */
+ WRITE_ONCE(hdmi->plugged_cb, fn);
+ WRITE_ONCE(hdmi->codec_dev, codec_dev);
mtk_hdmi_update_plugged_status(hdmi);
return 0;
--
2.25.0.225.g125e21ebc7-goog
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