linux-kernel - Re: [PATCH V6 3/6] drm: bridge: samsung-dsim: Fetch pll-clock-frequency automatically

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Date:   Wed, 17 May 2023 14:56:47 +0200
From:   Lucas Stach <l.stach@...gutronix.de>
To:     Adam Ford <aford173@...il.com>, dri-devel@...ts.freedesktop.org
Cc:     Marek Vasut <marex@...x.de>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Robert Foss <rfoss@...nel.org>,
        Jonas Karlman <jonas@...boo.se>, aford@...conembedded.com,
        Frieder Schrempf <frieder.schrempf@...tron.de>,
        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>,
        Jagan Teki <jagan@...rulasolutions.com>
Subject: Re: [PATCH V6 3/6] drm: bridge: samsung-dsim: Fetch
 pll-clock-frequency automatically

Hi Adam,

Am Montag, dem 15.05.2023 um 18:57 -0500 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.
> Since it can be optional, change the message from an error to
> dev_info.
> 
> Signed-off-by: Adam Ford <aford173@...il.com>
> Tested-by: Chen-Yu Tsai <wenst@...omium.org>
> Tested-by: Frieder Schrempf <frieder.schrempf@...tron.de>
> Reviewed-by: Frieder Schrempf <frieder.schrempf@...tron.de>
> ---
>  drivers/gpu/drm/bridge/samsung-dsim.c | 23 ++++++++++++++++-------
>  1 file changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
> index bf4b33d2de76..08266303c261 100644
> --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> @@ -1712,11 +1712,11 @@ static const struct mipi_dsi_host_ops samsung_dsim_ops = {
>  };
>  
>  static int samsung_dsim_of_read_u32(const struct device_node *np,
> -				    const char *propname, u32 *out_value)
> +				    const char *propname, u32 *out_value, bool optional)
>  {
>  	int ret = of_property_read_u32(np, propname, out_value);
>  
> -	if (ret < 0)
> +	if (ret < 0 && !optional)
>  		pr_err("%pOF: failed to get '%s' property\n", np, propname);
>  
>  	return ret;
> @@ -1726,20 +1726,29 @@ 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;
> +				       &dsi->pll_clk_rate, 1);
> +
> +	/* If it doesn't exist, read it from the clock instead of failing */
> +	if (ret < 0) {
> +		dev_info(dev, "Using sclk_mipi for pll clock frequency\n");

While this is certainly helpful while debugging the driver, I don't
think it warrants a info print. Remove or downgrade to dev_dbg?

On the other hand the changed driver behavior should be documented in
the devicetree binding by moving "samsung,pll-clock-frequency" into the
optional properties and spelling out which clock rate is used when the
property is absent.

Regards,
Lucas

> +		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);
> +	}
>  
>  	ret = samsung_dsim_of_read_u32(node, "samsung,burst-clock-frequency",
> -				       &dsi->burst_clk_rate);
> +				       &dsi->burst_clk_rate, 0);
>  	if (ret < 0)
>  		return ret;
>  
>  	ret = samsung_dsim_of_read_u32(node, "samsung,esc-clock-frequency",
> -				       &dsi->esc_clk_rate);
> +				       &dsi->esc_clk_rate, 0);
>  	if (ret < 0)
>  		return ret;
>