linux-kernel - Re: [PATCH] amba-clcd: add RGB444 support

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Date:	Mon, 15 Mar 2010 13:38:10 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Luotao Fu <l.fu@...gutronix.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andres Salomon <dilinger@...ian.org>,
	Alessandro Rubini <rubini@...pv.it>,
	Krzysztof Helt <krzysztof.h1@...pl>,
	Kevin Wells <wellsk40@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] amba-clcd: add RGB444 support

On Mon, Mar 15, 2010 at 02:30:09PM +0100, Luotao Fu wrote:
> This one adds RGB444 (bpp=12) support to amba clcd drivers. Tested on a lpc3250
> based platform.

No - this is wrong.  You have a 16bpp display.  bpp is the number of bits
in the framebuffer between two successive pixels.  It is not the number of
bits used for the pixel information.

The only case where you have a 12bpp display is if you have two pixels
packed into three bytes.

What you actually have is this arrangement:

111111
5432109876543210
....RRRRGGGGBBBB

where '....' are unused.

So, bpp = 16.  In order to work out whether you want RGB565, RGB555 or
RGB444, you have to look at the pixel format being requested in the
bitfield information.  I'd suggest looking at var->green.length:

                /*
                 * Green length can be 4, 5 or 6 depending whether
                 * we're operating in RGB444, RGB555 or RGB565 mode.
                 */
		if (var->green.length == 4) {
			var->blue.length = 4;
			var->red.length = 4;
		} else {
			var->blue.length = 5;
			var->red.length = 5;
			if (var->green.length != 5 && var->green.length != 6)
				var->green.length = 6;
		}

> 
> Signed-off-by: Luotao Fu <l.fu@...gutronix.de>
> ---
>  drivers/video/amba-clcd.c |   11 ++++++++---
>  include/linux/amba/clcd.h |    7 ++++++-
>  2 files changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/video/amba-clcd.c b/drivers/video/amba-clcd.c
> index a21efcd..5111a12 100644
> --- a/drivers/video/amba-clcd.c
> +++ b/drivers/video/amba-clcd.c
> @@ -134,6 +134,11 @@ clcdfb_set_bitfields(struct clcd_fb *fb, struct fb_var_screeninfo *var)
>  		var->blue.length	= var->bits_per_pixel;
>  		var->blue.offset	= 0;
>  		break;
> +	case 12:
> +		var->red.length		= 4;
> +		var->green.length	= 4;
> +		var->blue.length	= 4;
> +		break;
>  	case 16:
>  		var->red.length = 5;
>  		var->blue.length = 5;
> @@ -161,7 +166,7 @@ clcdfb_set_bitfields(struct clcd_fb *fb, struct fb_var_screeninfo *var)
>  	 * encoded in the pixel data.  Calculate their position from
>  	 * the bitfield length defined above.
>  	 */
> -	if (ret == 0 && var->bits_per_pixel >= 16) {
> +	if (ret == 0 && var->bits_per_pixel >= 12) {
>  		if (fb->panel->cntl & CNTL_BGR) {
>  			var->blue.offset = 0;
>  			var->green.offset = var->blue.offset + var->blue.length;
> @@ -200,6 +205,8 @@ static int clcdfb_set_par(struct fb_info *info)
>  	struct clcd_fb *fb = to_clcd(info);
>  	struct clcd_regs regs;
>  
> +	fb->board->decode(fb, &regs);
> +
>  	fb->fb.fix.line_length = fb->fb.var.xres_virtual *
>  				 fb->fb.var.bits_per_pixel / 8;
>  
> @@ -208,8 +215,6 @@ static int clcdfb_set_par(struct fb_info *info)
>  	else
>  		fb->fb.fix.visual = FB_VISUAL_TRUECOLOR;
>  
> -	fb->board->decode(fb, &regs);
> -
>  	clcdfb_disable(fb);
>  
>  	writel(regs.tim0, fb->regs + CLCD_TIM0);
> diff --git a/include/linux/amba/clcd.h b/include/linux/amba/clcd.h
> index 8d0d491..7e0bcc7 100644
> --- a/include/linux/amba/clcd.h
> +++ b/include/linux/amba/clcd.h
> @@ -53,6 +53,7 @@
>  #define CNTL_LCDBPP2		(1 << 1)
>  #define CNTL_LCDBPP4		(2 << 1)
>  #define CNTL_LCDBPP8		(3 << 1)
> +#define CNTL_LCDBPP12		(7 << 1)
>  #define CNTL_LCDBPP16		(4 << 1)
>  #define CNTL_LCDBPP16_565	(6 << 1)
>  #define CNTL_LCDBPP24		(5 << 1)
> @@ -209,6 +210,10 @@ static inline void clcdfb_decode(struct clcd_fb *fb, struct clcd_regs *regs)
>  	case 8:
>  		val |= CNTL_LCDBPP8;
>  		break;
> +	case 12:
> +		fb->fb.var.bits_per_pixel = 16;
> +		val |= CNTL_LCDBPP12;
> +		break;
>  	case 16:
>  		/*
>  		 * PL110 cannot choose between 5551 and 565 modes in
> @@ -225,7 +230,7 @@ static inline void clcdfb_decode(struct clcd_fb *fb, struct clcd_regs *regs)
>  		val |= CNTL_LCDBPP24;
>  		break;
>  	}
> -
> +	printk("**** %s: cntl val 0x%08x\n", __func__, val);
>  	regs->cntl = val;
>  	regs->pixclock = fb->fb.var.pixclock;
>  }
> -- 
> 1.7.0
> 
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