linux-kernel - Re: [PATCH 08/10] staging/xgifb: Remove unnecessary bitshifts in XGI

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Message-ID: <20130204125901.GH4937@mwanda>
Date:	Mon, 4 Feb 2013 15:59:01 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	Peter Huewe <peterhuewe@....de>
Cc:	Arnaud Patard <arnaud.patard@...-net.org>,
	devel@...verdev.osuosl.org, Aaro Koskinen <aaro.koskinen@....fi>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/10] staging/xgifb: Remove unnecessary bitshifts in
 XGI_SetCRT1ModeRegs

On Sun, Feb 03, 2013 at 10:54:37PM +0100, Peter Huewe wrote:
> Since data can only be 0x0000, 0x0035 or 0x0048 we can simply skip the
> bit shifting and masking as data & 0xFF is always equal to data and
> data & 0xFF00 is always 0.
> So we simply use data and 0 directly and save the assignment.
> 
> Signed-off-by: Peter Huewe <peterhuewe@....de>
> ---
>  drivers/staging/xgifb/vb_setmode.c |    6 ++----
>  1 files changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/staging/xgifb/vb_setmode.c b/drivers/staging/xgifb/vb_setmode.c
> index 6f366f4..1ff1178 100644
> --- a/drivers/staging/xgifb/vb_setmode.c
> +++ b/drivers/staging/xgifb/vb_setmode.c
> @@ -1083,10 +1083,8 @@ static void XGI_SetCRT1ModeRegs(struct xgi_hw_device_info *HwDeviceExtension,
>  			data = 0x0048;
>  	}
>  
> -	data2 = data & 0x00FF;
> -	xgifb_reg_and_or(pVBInfo->P3d4, 0x19, 0xFF, data2);
> -	data2 = (data & 0xFF00) >> 8;
> -	xgifb_reg_and_or(pVBInfo->P3d4, 0x19, 0xFC, data2);
> +	xgifb_reg_and_or(pVBInfo->P3d4, 0x19, 0xFF, data);
> +	xgifb_reg_and_or(pVBInfo->P3d4, 0x19, 0xFC, 0);

This patch is fine.

This is a fairly common pattern where people do:

	write_a_char(data & 0xff);
	write_a_char((data >> 8) & 0xff);

It feels there should be a macro to do the shift and mask but I'm
not sure what it would look like.

regards,
dan carpenter

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