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

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

[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@samsung.com>
---
 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));
 		/* it seems that both H and V scalers must be active
 		   to work correctly */
 		mode = (h || v) ? 0x30 : 0x00;
@@ -1583,17 +1597,6 @@ static int vidioc_g_chip_info(struct file *file, void *priv,
 	return 0;
 }
 
-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 vidioc_g_register(struct file *file, void *priv,
 			     struct v4l2_dbg_register *reg)
-- 
1.7.10.4

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

[Frank Schäfer]

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@samsung.com>
> ---
>  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.

Or do you know more than us, e.g. from looking into the datasheets ? ;-)

>  		/* it seems that both H and V scalers must be active
>  		   to work correctly */
>  		mode = (h || v) ? 0x30 : 0x00;
> @@ -1583,17 +1597,6 @@ static int vidioc_g_chip_info(struct file *file, void *priv,
>  	return 0;
>  }
>  
> -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 vidioc_g_register(struct file *file, void *priv,
>  			     struct v4l2_dbg_register *reg)

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@samsung.com>
>> ---
>>   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@samsung.com | (970) 672-0658

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

[Frank Schäfer]

Am 22.03.2014 16:22, schrieb 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@samsung.com>
>>> ---
>>>   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.

Well, almost all register writes use a hardcoded length (most of the
time it's 1). ;-)

>
> 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.

Yes, if the length would be variable, then this would be a good idea.
But AFAIK the length is always 2.

>
> 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 :)

I'm more concerned about the fact that readers of the code could think
that this is a write with a variable length, while the length is
actually always the same.

em28xx_reg_len() is a somewhat dirty hack for vidioc_[g,s]_register
debugging ioctls only.
Btw, what happens when you try to compile the code with this patch
applied and CONFIG_VIDEO_ADV_DEBUG disabled ? ;-)

Anyway, I very much appreciate your efforts to improve the em28xx
driver. :-)
There's much to do !

Regards,
Frank

>
> -- Shuah
>

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

[Shuah Khan]

On 03/22/2014 11:40 AM, Frank Schäfer wrote:
>
> I'm more concerned about the fact that readers of the code could think
> that this is a write with a variable length, while the length is
> actually always the same.

Fair enough.

>
> em28xx_reg_len() is a somewhat dirty hack for vidioc_[g,s]_register
> debugging ioctls only.

I didn't realize that. In that case, it doesn't make sense to propagate 
the change to non-debug code. This patch can be dropped. I thought 
em28xx_reg_len() is good example of finding register length for these 
registers.

> Btw, what happens when you try to compile the code with this patch
> applied and CONFIG_VIDEO_ADV_DEBUG disabled ? ;-)

CONFIG_VIDEO_ADV_DEBUG is disabled in my config.

-- Shuah


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