linux-kernel - Re: [PATCH v2 3/3] drm/tilcdc: fix pixel clock setting warning message

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Message-ID: <0d8770b6-755d-8fc7-4e52-2d745971876d@kernel.org>
Date:   Mon, 22 Mar 2021 09:26:49 +0200
From:   Tomi Valkeinen <tomba@...nel.org>
To:     Dario Binacchi <dariobin@...ero.it>, linux-kernel@...r.kernel.org
Cc:     Daniel Vetter <daniel@...ll.ch>, David Airlie <airlied@...ux.ie>,
        Jyri Sarha <jyri.sarha@....fi>, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2 3/3] drm/tilcdc: fix pixel clock setting warning
 message

On 21/03/2021 10:31, Dario Binacchi wrote:
> The warning message did not printed the LCD pixel clock rate but the LCD
> clock divisor input rate. As a consequence, the required and real pixel
> clock rates are now passed to the tilcdc_pclk_diff().
> 
> Signed-off-by: Dario Binacchi <dariobin@...ero.it>
> 
> ---
> 
> Changes in v2:
> - The patch has been added in version 2.
> 
>   drivers/gpu/drm/tilcdc/tilcdc_crtc.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
> index ac6228cb04d9..c0792c52dc02 100644
> --- a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
> +++ b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
> @@ -203,7 +203,7 @@ static void tilcdc_crtc_set_clk(struct drm_crtc *crtc)
>   	struct drm_device *dev = crtc->dev;
>   	struct tilcdc_drm_private *priv = dev->dev_private;
>   	struct tilcdc_crtc *tilcdc_crtc = to_tilcdc_crtc(crtc);
> -	unsigned long clk_rate, real_rate, real_pclk_rate, pclk_rate;
> +	unsigned long clk_rate, real_pclk_rate, pclk_rate;
>   	unsigned int clkdiv;
>   	int ret;
>   
> @@ -239,12 +239,12 @@ static void tilcdc_crtc_set_clk(struct drm_crtc *crtc)
>   		 * 5% is an arbitrary value - LCDs are usually quite tolerant
>   		 * about pixel clock rates.
>   		 */
> -		real_rate = clkdiv * pclk_rate;
> +		real_pclk_rate = clk_rate / clkdiv;
>   
> -		if (tilcdc_pclk_diff(clk_rate, real_rate) > 5) {
> +		if (tilcdc_pclk_diff(pclk_rate, real_pclk_rate) > 5) {
>   			dev_warn(dev->dev,
>   				 "effective pixel clock rate (%luHz) differs from the calculated rate (%luHz)\n",
> -				 clk_rate, real_rate);
> +				 pclk_rate, real_pclk_rate);

Aren't these backwards? "Effective" is the real one in the HW. I'm not 
sure what "calculated" means here, I guess it should be "requested".

  Tomi