linux-kernel - Re: [PATCH v4 3/3] drm/mediatek: fix the wrong pixel clock when resolution is 4K

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Date:   Mon, 12 Sep 2016 11:15:42 +0800
From:   CK Hu <ck.hu@...iatek.com>
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>,
        "Philipp Zabel" <p.zabel@...gutronix.de>,
        YT Shen <yt.shen@...iatek.com>,
        "Thierry Reding" <thierry.reding@...il.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 v4 3/3] drm/mediatek: fix the wrong pixel clock when
 resolution is 4K

Hi, Bibby:

Sorry for the late reply.

On Wed, 2016-08-17 at 14:58 +0800, Bibby Hsieh wrote:
> From: Junzhi Zhao <junzhi.zhao@...iatek.com>
> 
> Pixel clock should be 297MHz when resolution is 4K.
> 

>From the code you modified, I think title should be: "Enlarge pll_rate
range from (<original lower bound>, <original upper bound>) to (<new
lower bound>, <new upper bound>)"

In description, you can explain the pll_rate for 4K and this enlargement
could support more resolution include 4K (Not only 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 |    9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_dpi.c b/drivers/gpu/drm/mediatek/mtk_dpi.c
> index 0186e50..90fb831 100644
> --- a/drivers/gpu/drm/mediatek/mtk_dpi.c
> +++ b/drivers/gpu/drm/mediatek/mtk_dpi.c
> @@ -432,11 +432,16 @@ static int mtk_dpi_set_display_mode(struct mtk_dpi *dpi,
>  	unsigned long pll_rate;
>  	unsigned int factor;
>  
> +	/* let pll_rate can fix the valid range of tvdpll (1G~2GHz) */
>  	pix_rate = 1000UL * mode->clock;
> -	if (mode->clock <= 74000)
> +	if (mode->clock <= 27000)
> +		factor = 16 * 3;
> +	else if (mode->clock <= 84000)
>  		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",

Regards,
CK