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Thu, 13 Feb 2020 23:07:25 -0800 Received: from MTKMBS07N2.mediatek.inc (172.21.101.141) by MTKMBS62N1.mediatek.inc (172.29.193.41) with Microsoft SMTP Server (TLS) id 15.0.1395.4; Thu, 13 Feb 2020 23:07:37 -0800 Received: from mtkcas08.mediatek.inc (172.21.101.126) by mtkmbs07n2.mediatek.inc (172.21.101.141) with Microsoft SMTP Server (TLS) id 15.0.1395.4; Fri, 14 Feb 2020 15:06:38 +0800 Received: from [172.21.77.4] (172.21.77.4) by mtkcas08.mediatek.inc (172.21.101.73) with Microsoft SMTP Server id 15.0.1395.4 via Frontend Transport; Fri, 14 Feb 2020 15:07:21 +0800 Message-ID: <1581664042.20487.4.camel@mtksdaap41> Subject: Re: [PATCH] drm/mediatek: fix race condition for HDMI jack status reporting From: CK Hu To: Tzung-Bi Shih Date: Fri, 14 Feb 2020 15:07:22 +0800 In-Reply-To: <20200213153226.I477092c2f104fd589133436c3ae4590e6fc6323b@changeid> References: <20200213153226.I477092c2f104fd589133436c3ae4590e6fc6323b@changeid> X-Mailer: Evolution 3.10.4-0ubuntu2 MIME-Version: 1.0 X-MTK: N X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200213_230729_752057_7B3DD55D X-CRM114-Status: GOOD ( 16.44 ) X-BeenThere: linux-mediatek@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: alsa-devel@alsa-project.org, p.zabel@pengutronix.de, airlied@linux.ie, dri-devel@lists.freedesktop.org, broonie@kernel.org, linux-mediatek@lists.infradead.org, daniel@ffwll.ch, matthias.bgg@gmail.com, dgreid@google.com, linux-arm-kernel@lists.infradead.org, cychiang@google.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "Linux-mediatek" Errors-To: linux-mediatek-bounces+linux-mediatek=archiver.kernel.org@lists.infradead.org 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 > --- > 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 > #include > #include > +#include > #include > #include > #include > @@ -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); _______________________________________________ Linux-mediatek mailing list Linux-mediatek@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-mediatek