[PATCH] drm/mediatek: fix race condition for HDMI jack status reporting
From: Tzung-Bi Shih <hidden>
Date: 2020-02-13 08:00:24
Also in:
alsa-devel, dri-devel, linux-mediatek
Subsystem:
drm drivers, drm drivers for mediatek, the rest · Maintainers:
David Airlie, Simona Vetter, Chun-Kuang Hu, Philipp Zabel, Linus Torvalds
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 <redacted>
---
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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