linux-kernel - Re: [PATCH v6 3/4] drm/msm/dp: parser link-frequencies as property of dp

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Message-ID: <3ead3652-1241-89bd-3441-8ca4a4c8df57@linaro.org>
Date:   Thu, 1 Dec 2022 02:26:19 +0200
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, bjorn.andersson@...aro.org
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 v6 3/4] drm/msm/dp: parser link-frequencies as property of
 dp_out endpoint

On 01/12/2022 01:51, Kuogee Hsieh wrote:
> 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
> 
> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
> ---
>   drivers/gpu/drm/msm/dp/dp_parser.c | 16 ++++++++++++++++
>   drivers/gpu/drm/msm/dp/dp_parser.h |  2 ++
>   2 files changed, 18 insertions(+)
> 
> diff --git a/drivers/gpu/drm/msm/dp/dp_parser.c b/drivers/gpu/drm/msm/dp/dp_parser.c
> index b06ff60..2006341 100644
> --- a/drivers/gpu/drm/msm/dp/dp_parser.c
> +++ b/drivers/gpu/drm/msm/dp/dp_parser.c
> @@ -95,6 +95,7 @@ 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;
>   
>   	/*
> @@ -103,6 +104,7 @@ static int dp_parser_misc(struct dp_parser *parser)
>   	cnt = drm_of_get_data_lanes_count(of_node, 1, DP_MAX_NUM_DP_LANES);
>   	if (cnt > 0) {
>   		parser->max_dp_lanes = cnt;
> +		parser->max_dp_link_rate = DP_LINK_RATE_HBR2; /* 540000 khz */
>   		return 0;
>   	}
>   
> @@ -116,8 +118,22 @@ static int dp_parser_misc(struct dp_parser *parser)
>   			parser->max_dp_lanes = DP_MAX_NUM_DP_LANES; /* 4 lanes */
>   		else
>   			parser->max_dp_lanes = cnt;
> +
> +		cnt = of_property_count_u64_elems(endpoint, "link-frequencies");
> +		if (cnt < 0) {
> +			parser->max_dp_link_rate = DP_LINK_RATE_HBR2; /* 540000 khz */
> +		} else {
> +			if (cnt > DP_MAX_NUM_DP_LANES)
> +				cnt = DP_MAX_NUM_DP_LANES;

Why are you comparing the number of link frequencies with the number of 
lanes? You don't need the comparison at all.

> +
> +			of_property_read_u64_index(endpoint, "link-frequencies",
> +							cnt - 1, &frequency);

Checking of the return value?

> +
> +			parser->max_dp_link_rate = (frequency / 1000); /* kbits */
> +		}
>   	} else {
>   		parser->max_dp_lanes = DP_MAX_NUM_DP_LANES; /* 4 lanes */
> +		parser->max_dp_link_rate = DP_LINK_RATE_HBR2; /* 540000 khz */

Instead of having all the nested if's and setting of max_dp_link rate in 
several branches, please add a function that returns either a valid rate 
or an error. Then you can simply check the result of that function and 
set the default.

>   	}
>   
>   	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);

-- 
With best wishes
Dmitry