linux-kernel - Re: [PATCH v2 1/1] drm/mediatek: Add return value check when reading DPCD

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Message-ID: <CABnWg9tDMkKkFbQpL8YphOBu3_2zr_q4YASnO-UYMrdM22wCuQ@mail.gmail.com>
Date: Mon, 2 Dec 2024 03:38:07 -0600
From: Guillaume Ranquet <granquet@...libre.com>
To: Liankun Yang <liankun.yang@...iatek.com>, chunkuang.hu@...nel.org, 
	p.zabel@...gutronix.de, airlied@...il.com, simona@...ll.ch, 
	matthias.bgg@...il.com, angelogioacchino.delregno@...labora.com, 
	ck.hu@...iatek.com, dmitry.osipenko@...labora.com, rex-bc.chen@...iatek.com, 
	jitao.shi@...iatek.com, mac.shen@...iatek.com, peng.liu@...iatek.com, 
	Project_Global_Chrome_Upstream_Group@...iatek.com
Cc: dri-devel@...ts.freedesktop.org, linux-mediatek@...ts.infradead.org, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] drm/mediatek: Add return value check when reading DPCD

On Thu, 28 Nov 2024 04:08, Liankun Yang <liankun.yang@...iatek.com> wrote:
>Returns the number of bytes transferred (1) on success.
>Check the return value to confirm that AUX communication is successful.
>
>Fixes: d9e6ea02fc3f ("drm/mediatek: dp: Add MT8195 External DisplayPort support")
>
>Signed-off-by: Liankun Yang <liankun.yang@...iatek.com>
>---
>Changes in V2:
>- Modify Fixes in Commit Message.
>Per suggestion from the previous thread:
>https://patchwork.kernel.org/project/linux-mediatek/patch/20240930092000.5385-1-liankun.yang@mediatek.com/
>---
> drivers/gpu/drm/mediatek/mtk_dp.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
>diff --git a/drivers/gpu/drm/mediatek/mtk_dp.c b/drivers/gpu/drm/mediatek/mtk_dp.c
>index 1cc916b16471..9dc68ec2ff43 100644
>--- a/drivers/gpu/drm/mediatek/mtk_dp.c
>+++ b/drivers/gpu/drm/mediatek/mtk_dp.c
>@@ -2101,6 +2101,7 @@ static enum drm_connector_status mtk_dp_bdg_detect(struct drm_bridge *bridge)
> 	enum drm_connector_status ret = connector_status_disconnected;
> 	bool enabled = mtk_dp->enabled;
> 	u8 sink_count = 0;
>+	size_t value;
>
> 	if (!mtk_dp->train_info.cable_plugged_in)
> 		return ret;
>@@ -2115,7 +2116,12 @@ static enum drm_connector_status mtk_dp_bdg_detect(struct drm_bridge *bridge)
> 	 * function, we just need to check the HPD connection to check
> 	 * whether we connect to a sink device.
> 	 */
>-	drm_dp_dpcd_readb(&mtk_dp->aux, DP_SINK_COUNT, &sink_count);
>+	value = drm_dp_dpcd_readb(&mtk_dp->aux, DP_SINK_COUNT, &sink_count);
>+	if (value < 0) {
>+		drm_err(mtk_dp->drm_dev, "Failed to read DP Sink Count: %zd\n", value);
>+		return ret;
>+	}
>+
> 	if (DP_GET_SINK_COUNT(sink_count))
> 		ret = connector_status_connected;

Hi Liankun,

thx for your fix.
I think your patch could be improved by using the drm_dp_helper
function drm_dp_read_sink_count() ?

Thx,
Guillaume.

>
>--
>2.45.2