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

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  Re: [PATCH v3 3/3] drm/mediatek: fix the wrong pixel clock when  resolution is 4K Philipp Zabel <p.zabel@pengutronix.de> - 2016-08-11 09:20 +0200
    Re: [PATCH v3 3/3] drm/mediatek: fix the wrong pixel clock when  resolution is 4K Bibby Hsieh <bibby.hsieh@mediatek.com> - 2016-08-15 09:00 +0200

#1460210 — 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@mediatek.com>
> 
> Pixel clock should be 297MHz when resolution is 4K.
> 
> Signed-off-by: Junzhi Zhao <junzhi.zhao@mediatek.com>
> Signed-off-by: Bibby Hsieh <bibby.hsieh@mediatek.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

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#1462574

Hi, Philipp,

On Thu, 2016-08-11 at 09:15 +0200, Philipp Zabel wrote:
> Am Donnerstag, den 04.08.2016, 10:38 +0800 schrieb Bibby Hsieh:
> > From: Junzhi Zhao <junzhi.zhao@mediatek.com>
> > 
> > Pixel clock should be 297MHz when resolution is 4K.
> > 
> > Signed-off-by: Junzhi Zhao <junzhi.zhao@mediatek.com>
> > Signed-off-by: Bibby Hsieh <bibby.hsieh@mediatek.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 ?
> 
Because the valid range of tvdpll is from 1GHz to 2GHz, so, we have to
make the clock to fit that.

> regards
> Philipp
> 

-- 
Bibby

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