Re: [RESEND][PATCH] sm501fb: clear framebuffer memory and palette

[Ben Dooks <ben@fluff.org>]

On Mon, Jan 21, 2008 at 07:59:25PM +0900, Magnus Damm wrote:
> sm501fb: clear framebuffer memory and palette
> 
> Avoid displaying garbage on unused framebuffers. For most users a single
> framebuffer is used together with fbcon. sm501fb supports two framebuffers
> where one often is assigned to fbcon and the other one is left unused during
> the boot.
> 
> The problem here is that framebuffers not in use by fbcon happen to display
> garbage. This can easily be solved by making sure that framebuffer memory and
> palette ram are cleared.
> 
> The problem can be observed by using looking at the panel output (fb1)
> after booting the kernel with fbcon on crt (fb0). This is the default
> configuration. It's also possible to watch the garbage on the crt framebuffer
> by passing "fbcon=map:1" on the kernel cmdline. This will assign fbcon to
> the panel (fb1) and leave the crt (fb0) unused.

Can you please add a no-clear-on-init flag incase people do not want
their framebuffers cleared.
 
> Signed-off-by: Magnus Damm <damm@igel.co.jp>
> ---
> 
>  This is the same patch that was sent to linux-fbdev-devel on 20071228.
> 
>  drivers/video/sm501fb.c |    8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> --- 0002/drivers/video/sm501fb.c
> +++ work/drivers/video/sm501fb.c	2007-12-27 13:24:20.000000000 +0900
> @@ -1264,6 +1264,7 @@ static int sm501fb_start(struct sm501fb_
>  {
>  	struct resource	*res;
>  	struct device *dev;
> +	int k;
>  	int ret;
>  
>  	info->dev = dev = &pdev->dev;
> @@ -1325,6 +1326,13 @@ static int sm501fb_start(struct sm501fb_
>  
>  	info->fbmem_len = (res->end - res->start)+1;
>  
> +	/* clear framebuffer memory - avoids garbage data on unused fb */
> +	memset(info->fbmem, 0, info->fbmem_len);
> +
> +	/* clear palette ram - undefined at power on */
> +	for (k = 0; k < (256 * 3); k++)
> +		writel(0, info->regs + SM501_DC_PANEL_PALETTE + (k * 4));
> +
>  	/* enable display controller */
>  	sm501_unit_power(dev->parent, SM501_GATE_DISPLAY, 1);
>  
> 
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-- 
Ben (ben@fluff.org, http://www.fluff.org/)

  'a smiley only costs 4 bytes'

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