Hi, Tzung-Bi:
On Thu, 2020-02-13 at 15:59 +0800, Tzung-Bi Shih wrote:
> 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 <tzun...@google.com>
> ---
> 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)
I think sound driver could be removed for some reason, and fn should be
set to NULL before sound driver removed. In this case, codec_dev != NULL
and fn == NULL.
Regards,
CK
> + 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);
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