linux-kernel - Re: [PATCH v1 3/6] drm/mediatek: mtk_dpi: Use an array for pixclk factor calculation

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Message-ID: <120c65e7c21821a72fa5165e578cc1c39cf0c864.camel@mediatek.com>
Date: Fri, 22 Nov 2024 06:23:44 +0000
From: CK Hu (胡俊光) <ck.hu@...iatek.com>
To: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	"chunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>
CC: "linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>, "simona@...ll.ch"
	<simona@...ll.ch>, "tzimmermann@...e.de" <tzimmermann@...e.de>,
	"mripard@...nel.org" <mripard@...nel.org>,
	Jitao Shi (石记涛) <jitao.shi@...iatek.com>,
	"kernel@...labora.com" <kernel@...labora.com>, "p.zabel@...gutronix.de"
	<p.zabel@...gutronix.de>, "maarten.lankhorst@...ux.intel.com"
	<maarten.lankhorst@...ux.intel.com>, "conor+dt@...nel.org"
	<conor+dt@...nel.org>, "robh@...nel.org" <robh@...nel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
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	<linux-arm-kernel@...ts.infradead.org>, "matthias.bgg@...il.com"
	<matthias.bgg@...il.com>, "krzk+dt@...nel.org" <krzk+dt@...nel.org>
Subject: Re: [PATCH v1 3/6] drm/mediatek: mtk_dpi: Use an array for pixclk
 factor calculation

Hi, Angelo:

On Fri, 2024-11-22 at 11:54 +0800, CK Hu wrote:
> Hi, Angelo:
> 
> On Wed, 2024-11-20 at 13:44 +0100, AngeloGioacchino Del Regno wrote:
> > External email : Please do not click links or open attachments until you have verified the sender or the content.
> > 
> > 
> > Setting the TVD PLL clock requires to multiply the target pixel
> > clock by a specific constant factor to achieve the target PLL
> > frequency, and this is done to reduce jitter to acceptable levels.
> > 
> > On all MediaTek SoCs, the factor is not retrieved by any real kind
> > of calculation but rather by checking if the target pixel clock
> > is less than a specified frequency, hence assigning a function
> > pointer for just a bunch of if branches does enlarge the code
> > size for little reason.
> > 
> > Remove all SoC-specific functions, add a structure `mtk_dpi_factor`
> > that holds a clock frequency and corresponding PLL factor, and
> > declare the constraints for each SoC in form of an array of said
> > structure.
> > Instead of function pointers, this structure (and its size) is then
> > assigned to each SoC's platform data.
> > 
> > The "calculation" is then performed with a new static function
> > mtk_dpi_calculate_factor(dpi, mode_clk) that iterates through all
> > of the entries of the aforementioned array and returns the right
> > factor.
> > 
> > If no factor is found, the lowest possible factor is returned,
> > mimicking the same flow as all of the old per-SoC calculation
> > functions.
> > 
> > This commit brings no functional change.
> 

[snip]

> >  static int mtk_dpi_set_display_mode(struct mtk_dpi *dpi,
> >                                     struct drm_display_mode *mode)
> >  {
> > @@ -529,7 +550,7 @@ static int mtk_dpi_set_display_mode(struct mtk_dpi *dpi,
> >         unsigned int factor;
> > 
> >         /* let pll_rate can fix the valid range of tvdpll (1G~2GHz) */
> > -       factor = dpi->conf->cal_factor(mode->clock);
> > +       factor = mtk_dpi_calculate_factor(dpi, mode_clk);

mode_clk is defined in next patch.
keep mode->clock in this patch to keep my reviewed-by tag.

Regards,
CK

> >         drm_display_mode_to_videomode(mode, &vm);
> >         pll_rate = vm.pixelclock * factor;
> > 
> > @@ -964,48 +985,6 @@ static const struct component_ops mtk_dpi_component_ops = {
> >         .unbind = mtk_dpi_unbind,
> >  };
> >