linux-kernel - Re: [PATCH v3 3/3] drm/mediatek: fix the wrong pixel clock when resolution is 4K

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Date:	Thu, 11 Aug 2016 09:15:12 +0200
From:	Philipp Zabel <p.zabel@...gutronix.de>
To:	Bibby Hsieh <bibby.hsieh@...iatek.com>
Cc:	David Airlie <airlied@...ux.ie>,
	Matthias Brugger <matthias.bgg@...il.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	dri-devel@...ts.freedesktop.org,
	linux-mediatek@...ts.infradead.org,
	Yingjoe Chen <yingjoe.chen@...iatek.com>,
	Cawa Cheng <cawa.cheng@...iatek.com>,
	Daniel Kurtz <djkurtz@...omium.org>,
	YT Shen <yt.shen@...iatek.com>,
	Thierry Reding <thierry.reding@...il.com>,
	CK Hu <ck.hu@...iatek.com>, Mao Huang <littlecvr@...omium.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Sascha Hauer <kernel@...gutronix.de>,
	Junzhi Zhao <junzhi.zhao@...iatek.com>
Subject: Re: [PATCH v3 3/3] drm/mediatek: fix the wrong pixel clock when
 resolution is 4K

Am Donnerstag, den 04.08.2016, 10:38 +0800 schrieb Bibby Hsieh:
> From: Junzhi Zhao <junzhi.zhao@...iatek.com>
> 
> Pixel clock should be 297MHz when resolution is 4K.
> 
> Signed-off-by: Junzhi Zhao <junzhi.zhao@...iatek.com>
> Signed-off-by: Bibby Hsieh <bibby.hsieh@...iatek.com>
> ---
>  drivers/gpu/drm/mediatek/mtk_dpi.c |    8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_dpi.c b/drivers/gpu/drm/mediatek/mtk_dpi.c
> index d05ca79..a90af59 100644
> --- a/drivers/gpu/drm/mediatek/mtk_dpi.c
> +++ b/drivers/gpu/drm/mediatek/mtk_dpi.c
> @@ -438,10 +438,14 @@ static int mtk_dpi_set_display_mode(struct mtk_dpi *dpi,
>  	}
>  
>  	pix_rate = 1000UL * mode->clock;
> -	if (mode->clock <= 74000)
> +	if (mode->clock <= 27000)
> +		factor = 16 * 3;
> +	else if (mode->clock <= 74250)
>  		factor = 8 * 3;
> -	else
> +	else if (mode->clock <= 167000)
>  		factor = 4 * 3;
> +	else
> +		factor = 2 * 3;
>  	pll_rate = pix_rate * factor;
>  
>  	dev_dbg(dpi->dev, "Want PLL %lu Hz, pixel clock %lu Hz\n",

Could you add a comment why this also changes the 74 MHz limit to 74.25
MHz and that adds a factor 16*3 for clocks <= 27 MHz ?

regards
Philipp