linux-kernel - Re: [PATCH v9 4/5] drm/msm/dp: parser link-frequencies as property of dp

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Message-ID: <90C493B1-E7E3-46A9-89F0-443922B8FEF5@linaro.org>
Date:   Tue, 06 Dec 2022 02:41:21 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Kuogee Hsieh <quic_khsieh@...cinc.com>,
        dri-devel@...ts.freedesktop.org, robdclark@...il.com,
        sean@...rly.run, swboyd@...omium.org, dianders@...omium.org,
        vkoul@...nel.org, daniel@...ll.ch, airlied@...ux.ie,
        agross@...nel.org, andersson@...nel.org,
        konrad.dybcio@...ainline.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, devicetree@...r.kernel.org,
        airlied@...il.com
CC:     quic_abhinavk@...cinc.com, quic_sbillaka@...cinc.com,
        freedreno@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 4/5] drm/msm/dp: parser link-frequencies as property of dp_out endpoint

6 декабря 2022 г. 02:08:13 GMT+03:00, Kuogee Hsieh <quic_khsieh@...cinc.com> пишет:
>Add capability to parser and retrieve max DP link supported rate from
>link-frequencies property of dp_out endpoint.
>
>Changes in v6:
>-- second patch after split parser patch into two patches
>
>Changes in v7:
>-- without checking cnt against DP_MAX_NUM_DP_LANES to retrieve link rate
>
>Changes in v9:
>-- separate parser link-frequencies out of data-lanes
>
>Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
>---
> drivers/gpu/drm/msm/dp/dp_parser.c | 20 ++++++++++++++++++--
> drivers/gpu/drm/msm/dp/dp_parser.h |  2 ++
> 2 files changed, 20 insertions(+), 2 deletions(-)
>
>diff --git a/drivers/gpu/drm/msm/dp/dp_parser.c b/drivers/gpu/drm/msm/dp/dp_parser.c
>index b5f7e70..fdea843 100644
>--- a/drivers/gpu/drm/msm/dp/dp_parser.c
>+++ b/drivers/gpu/drm/msm/dp/dp_parser.c
>@@ -94,15 +94,17 @@ static int dp_parser_ctrl_res(struct dp_parser *parser)
> static int dp_parser_misc(struct dp_parser *parser)
> {
> 	struct device_node *of_node = parser->pdev->dev.of_node;
>+	struct device_node *endpoint;
>+	u64 frequency;
> 	int cnt;
> 
> 	/*
> 	 * data-lanes is the property of dp_out endpoint
> 	 */
> 	cnt = drm_of_get_data_lanes_count_ep(of_node, 1, 0, 1, DP_MAX_NUM_DP_LANES);
>-	if (cnt > 0)
>+	if (cnt > 0) {
> 		parser->max_dp_lanes = cnt;
>-	else {
>+	} else {

This belongs to the previous patch 

> 		/*
> 		 * legacy code, data-lanes is the property of mdss_dp node
> 		 */
>@@ -113,6 +115,20 @@ static int dp_parser_misc(struct dp_parser *parser)
> 			parser->max_dp_lanes = DP_MAX_NUM_DP_LANES; /* 4 lanes */
> 	}
> 
>+	cnt = 0;
>+	endpoint = of_graph_get_endpoint_by_regs(of_node, 1, 0); /* port@1 */
>+	if (endpoint)
>+		cnt = of_property_count_u64_elems(endpoint, "link-frequencies");
>+	of_node_put(endpoint);
>+	if (cnt > 0) {
>+		of_property_read_u64_index(endpoint, "link-frequencies",

And this is use after free.

I still think than an additional function would make code simpler. You can return an error code at any point. And then handle it in the calling code.

>+						cnt - 1, &frequency);
>+		frequency /= 10;	/* from symbol rate to link rate */
>+		parser->max_dp_link_rate = (frequency / 1000); /* kbits */
>+	} else {
>+		parser->max_dp_link_rate = DP_LINK_RATE_HBR2; /* 540000 khz */
>+	}
>+
> 	return 0;
> }
> 
>diff --git a/drivers/gpu/drm/msm/dp/dp_parser.h b/drivers/gpu/drm/msm/dp/dp_parser.h
>index 866c1a8..3ddf639 100644
>--- a/drivers/gpu/drm/msm/dp/dp_parser.h
>+++ b/drivers/gpu/drm/msm/dp/dp_parser.h
>@@ -15,6 +15,7 @@
> #define DP_LABEL "MDSS DP DISPLAY"
> #define DP_MAX_PIXEL_CLK_KHZ	675000
> #define DP_MAX_NUM_DP_LANES	4
>+#define DP_LINK_RATE_HBR2       540000
> 
> enum dp_pm_type {
> 	DP_CORE_PM,
>@@ -119,6 +120,7 @@ struct dp_parser {
> 	struct dp_io io;
> 	struct dp_display_data disp_data;
> 	u32 max_dp_lanes;
>+	u32 max_dp_link_rate;
> 	struct drm_bridge *next_bridge;
> 
> 	int (*parse)(struct dp_parser *parser);