linux-kernel - Re: [PATCH] atmel-lcdc: Fix pixclock upper bound detection

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Message-ID: <4A0966D8.3080100@atmel.com>
Date:	Tue, 12 May 2009 14:08:56 +0200
From:	Nicolas Ferre <nicolas.ferre@...el.com>
To:	Ben Nizette <bn@...sdigital.com>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	Haavard Skinnemoen <hskinnemoen@...el.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	kernel <kernel@...32linux.org>
Subject: Re: [PATCH] atmel-lcdc: Fix pixclock upper bound detection

Ben Nizette :
> AFAICT the code which checks that the requested pixclock value is within
> bounds is incorrect.  It ensures that the lcdc core clock is at least
> (bytes per pixel) times higher than the pixel clock rather than just
> greater than or equal to.
> 
> There are tighter restrictions on the pixclock value as a function of
> bus width for STN panels but even then it isn't a simple relationship as
> currently checked for.  IMO either something like the below patch should
> be applied or else more detailed checking logic should be implemented
> which takes in to account the panel type as well.
> 
> CMIIW :-)
> 
> Signed-off-by: Ben Nizette <bn@...sdigital.com>

Acked-by: Nicolas Ferre <nicolas.ferre@...el.com>

> ---
> diff --git a/drivers/video/atmel_lcdfb.c b/drivers/video/atmel_lcdfb.c
> index 9a577a8..5779641 100644
> --- a/drivers/video/atmel_lcdfb.c
> +++ b/drivers/video/atmel_lcdfb.c
> @@ -351,7 +351,7 @@ static int atmel_lcdfb_check_var(struct fb_var_screeninfo *var,
>  	dev_dbg(dev, "  bpp:        %u\n", var->bits_per_pixel);
>  	dev_dbg(dev, "  clk:        %lu KHz\n", clk_value_khz);
>  
> -	if ((PICOS2KHZ(var->pixclock) * var->bits_per_pixel / 8) > clk_value_khz) {
> +	if (PICOS2KHZ(var->pixclock) > clk_value_khz) {
>  		dev_err(dev, "%lu KHz pixel clock is too fast\n", PICOS2KHZ(var->pixclock));
>  		return -EINVAL;
>  	}
> 
> 
> 


-- 
Nicolas Ferre
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