linux-kernel - Re: [PATCH 1/9] drm/panel: simple: add a macro for defining display modes in a simpler and less error prone way

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Message-ID: <20171017120818.GB684@ulmo>
Date:   Tue, 17 Oct 2017 14:08:18 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Lothar Waßmann <LW@...O-electronics.de>
Cc:     David Airlie <airlied@...ux.ie>,
        Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/9] drm/panel: simple: add a macro for defining display
 modes in a simpler and less error prone way

On Wed, Oct 11, 2017 at 01:23:33PM +0200, Lothar Waßmann wrote:
> Create a macro that eases the definition of display mode parameters by
> accecpting the parameters:
> freq, hactive, hfront-porch, hsynclen, hback-porch,
> vactive, vfront-porch, vsynclen, vback-porch, vrefresh
> that can be usually directly taken from an LCD datasheet.
> 
> Put the calculations that are now open coded repeating the same
> parameters multiple times into the macro expansion.
> 
> Signed-off-by: Lothar Waßmann <LW@...O-electronics.de>
> ---
>  drivers/gpu/drm/panel/panel-simple.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
> index 474fa75..dec639d 100644
> --- a/drivers/gpu/drm/panel/panel-simple.c
> +++ b/drivers/gpu/drm/panel/panel-simple.c
> @@ -411,6 +411,20 @@ static const struct panel_desc ampire_am_480272h3tmqw_t01h = {
>  	.bus_format = MEDIA_BUS_FMT_RGB888_1X24,
>  };
>  
> +#define SP_DISPLAY_MODE(freq, ha, hfp, hs, hbp, va, vfp, vs, vbp, vr, flgs) { \
> +	.clock = freq,							\
> +	.hdisplay = ha,							\
> +	.hsync_start = (ha) + (hfp),					\
> +	.hsync_end = (ha) + (hfp) + (hs),				\
> +	.htotal = (ha) + (hfp) + (hs) + (hbp),				\
> +	.vdisplay = (va),						\
> +	.vsync_start = (va) + (vfp),					\
> +	.vsync_end = (va) + (vfp) + (vs),				\
> +	.vtotal = (va) + (vfp) + (vs) + (vbp),				\
> +	.vrefresh = vr,							\
> +	.flags = flgs,							\
> +	}

I don't think this simplifies anything. It's now completely non-obvious
which parameter is which, so you actually have to go look at the macro
definition when you add a new mode to make sure you get them right.

Thierry

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