Re: [PATCH] media: em28xx-video - change em28xx_scaler_set() to use em28xx_reg_len()

[Shuah Khan]

On 03/22/2014 06:32 AM, Frank Schäfer wrote:
> Am 21.03.2014 22:04, schrieb Shuah Khan:
> > Change em28xx_scaler_set() to use em28xx_reg_len() to get register
> > lengths for EM28XX_R30_HSCALELOW and EM28XX_R32_VSCALELOW registers,
> > instead of hard-coding the length. Moved em28xx_reg_len() definition
> > for it to be visible to em28xx_scaler_set().
> >
> > Signed-off-by: Shuah Khan <shuah.kh@xxxxxxxxxxx>
> > ---
> >   drivers/media/usb/em28xx/em28xx-video.c |   29 ++++++++++++++++-------------
> >   1 file changed, 16 insertions(+), 13 deletions(-)
> >
> > diff --git a/drivers/media/usb/em28xx/em28xx-video.c b/drivers/media/usb/em28xx/em28xx-video.c
> > index 19af6b3..f8a91de 100644
> > --- a/drivers/media/usb/em28xx/em28xx-video.c
> > +++ b/drivers/media/usb/em28xx/em28xx-video.c
> > @@ -272,6 +272,18 @@ static void em28xx_capture_area_set(struct em28xx *dev, u8 hstart, u8 vstart,
> >   	}
> >   }
> >
> > +static int em28xx_reg_len(int reg)
> > +{
> > +	switch (reg) {
> > +	case EM28XX_R40_AC97LSB:
> > +	case EM28XX_R30_HSCALELOW:
> > +	case EM28XX_R32_VSCALELOW:
> > +		return 2;
> > +	default:
> > +		return 1;
> > +	}
> > +}
> > +
> >   static int em28xx_scaler_set(struct em28xx *dev, u16 h, u16 v)
> >   {
> >   	u8 mode;
> > @@ -284,11 +296,13 @@ static int em28xx_scaler_set(struct em28xx *dev, u16 h, u16 v)
> >
> >   		buf[0] = h;
> >   		buf[1] = h >> 8;
> > -		em28xx_write_regs(dev, EM28XX_R30_HSCALELOW, (char *)buf, 2);
> > +		em28xx_write_regs(dev, EM28XX_R30_HSCALELOW, (char *)buf,
> > +				  em28xx_reg_len(EM28XX_R30_HSCALELOW));
> >
> >   		buf[0] = v;
> >   		buf[1] = v >> 8;
> > -		em28xx_write_regs(dev, EM28XX_R32_VSCALELOW, (char *)buf, 2);
> > +		em28xx_write_regs(dev, EM28XX_R32_VSCALELOW, (char *)buf,
> > +				  em28xx_reg_len(EM28XX_R32_VSCALELOW));
> Hmm... registers 0x30 and 0x32 are always 2 bytes long.
> So this change would needlessly complicate the code.

The reason I made the change is that em28xx_reg_len() is handling these 
two registers and I thought it would be good to make it consistent with 
other writes to these registers and not hard-code the length.

I think it would help with maintenance later by avoiding hard-coding the 
length and use the existing routine that returns the length for these 
registers.

You are correct that it does add a function call in the code path. So if 
you think the trade-off isn't worth it, I am not going to argue with it :)

-- Shuah

--
Shuah Khan
Senior Linux Kernel Developer - Open Source Group
Samsung Research America(Silicon Valley)
shuah.kh@xxxxxxxxxxx | (970) 672-0658
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