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

["CK Hu (胡俊光)" <ck.hu@mediatek.com>]

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,
> >  };
> >