linux-kernel - Re: [PATCH v10 4/5] drm/msm/dp: parser link-frequencies as property of dp

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Date:   Wed, 7 Dec 2022 22:13:23 +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, 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 v10 4/5] drm/msm/dp: parser link-frequencies as property
 of dp_out endpoint

On 07/12/2022 18:57, 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
> 
> 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
> 
> Changes in v10:
> -- add dp_parser_link_frequencies()
> 
> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
> ---
>   drivers/gpu/drm/msm/dp/dp_parser.c | 27 +++++++++++++++++++++++++++
>   drivers/gpu/drm/msm/dp/dp_parser.h |  2 ++
>   2 files changed, 29 insertions(+)
> 
> diff --git a/drivers/gpu/drm/msm/dp/dp_parser.c b/drivers/gpu/drm/msm/dp/dp_parser.c
> index b5f7e70..9398abe 100644
> --- a/drivers/gpu/drm/msm/dp/dp_parser.c
> +++ b/drivers/gpu/drm/msm/dp/dp_parser.c
> @@ -91,6 +91,28 @@ static int dp_parser_ctrl_res(struct dp_parser *parser)
>   	return 0;
>   }
>   
> +static u32 dp_parser_link_frequencies(struct device_node *of_node)
> +{
> +	struct device_node *endpoint;
> +	u64 frequency = 0;
> +	int cnt = 0;
> +
> +	endpoint = of_graph_get_endpoint_by_regs(of_node, 1, 0); /* port@1 */

if (!endpoint)
   return -ENODEV; (or 0, as you have u32)

It's much easier IMO.

> +	if (endpoint)
> +		cnt = of_property_count_u64_elems(endpoint, "link-frequencies");
> +
> +	if (cnt > 0) {
> +		of_property_read_u64_index(endpoint, "link-frequencies",
> +						cnt - 1, &frequency);
> +		frequency /= 10;	/* from symbol rate to link rate */
> +		frequency /= 1000;	/* kbits */

kbytes?

> +	}
> +
> +	of_node_put(endpoint);

Even easier:

cnt = of_property_count(...);
if (cnt > 0)
     of_property_read_u64_index(...);
of_node_put(endpoint);

frequency /= 10;
frequency /= 1000;

return frequency;

> +
> +	return (u32)frequency;
> +}
> +
>   static int dp_parser_misc(struct dp_parser *parser)
>   {
>   	struct device_node *of_node = parser->pdev->dev.of_node;
> @@ -113,6 +135,11 @@ static int dp_parser_misc(struct dp_parser *parser)
>   			parser->max_dp_lanes = DP_MAX_NUM_DP_LANES; /* 4 lanes */
>   	}
>   
> +	parser->max_dp_link_rate = dp_parser_link_frequencies(of_node);
> +

Drop the empty line please. The if checks the result of the previous 
assignment. It's easier to comprehend if they visually belong to the 
same code block.

> +	if (!parser->max_dp_link_rate)
> +                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..6b10c3e 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 /* khz */
>   
>   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