hdmi_conn_detect and mtk_hdmi_audio_hook_plugged_cb would be called
by different threads.
Imaging the following calling sequence:
Thread A Thread B
--------------------------------------------------------------------
mtk_hdmi_audio_hook_plugged_cb()
mtk_cec_hpd_high() -> disconnected
hdmi_conn_detect()
mtk_cec_hpd_high() -> connected
plugged_cb(connected)
plugged_cb(disconnected)
The latest disconnected is false reported. Makes mtk_cec_hpd_high
and plugged_cb atomic to fix.
plugged_cb and codec_dev are also in danger of race condition. Instead
of using mutex to protect them:
- 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.
Fixes: 5d3c64477392 ("drm/mediatek: support HDMI jack status reporting")
Signed-off-by: Tzung-Bi Shih <tzungbi@xxxxxxxxxx>
---
Previous discussion: https://patchwork.kernel.org/patch/11367625/
Previous attempt: https://patchwork.kernel.org/patch/11378413/
drivers/gpu/drm/mediatek/mtk_hdmi.c | 18 ++++++++++++++----
1 file changed, 14 insertions(+), 4 deletions(-)
diff --git a/drivers/gpu/drm/mediatek/mtk_hdmi.c b/drivers/gpu/drm/mediatek/mtk_hdmi.c
index 03aeb73005ef..b1e5d0c538fa 100644
--- a/drivers/gpu/drm/mediatek/mtk_hdmi.c
+++ b/drivers/gpu/drm/mediatek/mtk_hdmi.c
@@ -12,6 +12,7 @@
#include <linux/io.h>
#include <linux/kernel.h>
#include <linux/mfd/syscon.h>
+#include <linux/mutex.h>
#include <linux/of_platform.h>
#include <linux/of.h>
#include <linux/of_gpio.h>
@@ -171,6 +172,7 @@ struct mtk_hdmi {
bool enabled;
hdmi_codec_plugged_cb plugged_cb;
struct device *codec_dev;
+ struct mutex update_plugged_status_lock;
};
static inline struct mtk_hdmi *hdmi_ctx_from_bridge(struct drm_bridge *b)
@@ -1199,10 +1201,13 @@ static void mtk_hdmi_clk_disable_audio(struct mtk_hdmi *hdmi)
static enum drm_connector_status
mtk_hdmi_update_plugged_status(struct mtk_hdmi *hdmi)
{
- bool connected = mtk_cec_hpd_high(hdmi->cec_dev);
+ bool connected;
- if (hdmi->plugged_cb && hdmi->codec_dev)
+ mutex_lock(&hdmi->update_plugged_status_lock);
+ connected = mtk_cec_hpd_high(hdmi->cec_dev);
+ if (hdmi->codec_dev)
hdmi->plugged_cb(hdmi->codec_dev, connected);
+ mutex_unlock(&hdmi->update_plugged_status_lock);
return connected ?
connector_status_connected : connector_status_disconnected;
@@ -1669,8 +1674,12 @@ 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;
@@ -1729,6 +1738,7 @@ static int mtk_drm_hdmi_probe(struct platform_device *pdev)
return ret;
}
+ mutex_init(&hdmi->update_plugged_status_lock);
platform_set_drvdata(pdev, hdmi);
ret = mtk_hdmi_output_init(hdmi);
--
2.25.0.225.g125e21ebc7-goog
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