linux-kernel - Re: [PATCH V3 3/7] drm: bridge: samsung-dsim: Fetch pll-clock-frequency automatically

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Message-ID: <7519081.EvYhyI6sBW@steina-w>
Date:   Thu, 04 May 2023 11:21:30 +0200
From:   Alexander Stein <alexander.stein@...tq-group.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     marex@...x.de, Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Jonas Karlman <jonas@...boo.se>, aford@...conembedded.com,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        linux-kernel@...r.kernel.org,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Chen-Yu Tsai <wenst@...omium.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Adam Ford <aford173@...il.com>,
        Jagan Teki <jagan@...rulasolutions.com>,
        Adam Ford <aford173@...il.com>
Subject: Re: [PATCH V3 3/7] drm: bridge: samsung-dsim: Fetch pll-clock-frequency automatically

Am Dienstag, 2. Mai 2023, 03:07:55 CEST schrieb Adam Ford:
> Make the pll-clock-frequency optional.  If it's present, use it
> to maintain backwards compatibility with existing hardware.  If it
> is absent, read clock rate of "sclk_mipi" to determine the rate.
> 
> Signed-off-by: Adam Ford <aford173@...il.com>
> Tested-by: Chen-Yu Tsai <wenst@...omium.org>
> ---
>  drivers/gpu/drm/bridge/samsung-dsim.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c
> b/drivers/gpu/drm/bridge/samsung-dsim.c index bf4b33d2de76..2dc02a9e37c0
> 100644
> --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> @@ -1726,12 +1726,20 @@ static int samsung_dsim_parse_dt(struct samsung_dsim
> *dsi) {
>  	struct device *dev = dsi->dev;
>  	struct device_node *node = dev->of_node;
> +	struct clk *pll_clk;
>  	int ret;
> 
>  	ret = samsung_dsim_of_read_u32(node, "samsung,pll-clock-frequency",
>  				       &dsi->pll_clk_rate);
> -	if (ret < 0)
> -		return ret;
> +
> +	/* If it doesn't exist, read it from the clock instead of failing */
> +	if (ret < 0) {
> +		pll_clk = devm_clk_get(dev, "sclk_mipi");
> +		if (!IS_ERR(pll_clk))
> +			dsi->pll_clk_rate = clk_get_rate(pll_clk);
> +		else
> +			return PTR_ERR(pll_clk);
> +	}
> 

Now that 'samsung,pll-clock-frequency' is optional the error in 
samsung_dsim_of_read_u32() should be changed. Otherwise you will get
> /soc@...us@...00000/dsi@...10000: failed to get 'samsung,pll-clock-
frequency' property

Best regards,
Alexander

>  	ret = samsung_dsim_of_read_u32(node, "samsung,burst-clock-
frequency",
>  				       &dsi->burst_clk_rate);


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