Re: [PATCH 1/2] media: atmel-isi: setup the ISI_CFG2 register directly

[Josh Wu <josh.wu@atmel.com>]

Hi, Guennadi

Thanks for the review.

On 8/30/2015 4:48 PM, Guennadi Liakhovetski wrote:
> Hi Josh,
>
> On Wed, 17 Jun 2015, Josh Wu wrote:
>
>> In the function configure_geometry(), we will setup the ISI CFG2
>> according to the sensor output format.
>>
>> It make no sense to just read back the CFG2 register and just set part
>> of it.
>>
>> So just set up this register directly makes things simpler.
> Simpler doesn't necessarily mean better or more correct:) There are other
> fields in that register and currently the driver preserves them, with this
> patch you overwrite them with 0. 0 happens to be the reset value of that
> register. So, you should at least mention that in this patch description,
> just saying "simpler" doesn't convince me.

Correct, I should mention that the reset value (0) of cfg2 means the YUV 
mode in the commit message.
To use YUV mode we need to clear COL_SPACE (bit 15 of CFG2) and since 
the reset value is 0, so in the code, I didn't need do anything.

> So, at least I'd modify that, I
> can do that myself. But in general I'm not even sure why this patch is
> needed. Yes, currently those fields of that register are unused, so, we
> can assume they stay at their reset values. But firstly the hardware can
> change and at some point the reset value can change, or those other fields
> will get set indirectly by something. Or the driver will change at some
> point to support more fields of that register and then this code will have
> to be changed again.

I understand your concern.
maybe a better solution is explicitly set the COL_SPACE (bit 15) to 0 
for the YUV formats. like:

#define ISI_CFG2_COL_SPACE_YUV        (0 << 15)

case MEDIA_BUS_FMT_YVYU8_2X8:
     cfg2 = ISI_CFG2_COL_SPACE_YUV | ISI_CFG2_YCC_SWAP_MODE_1;
     break;

And above modifications can be sent with RGB format support patch in future.

> So, I'd ask you again - do you really want this
> patch?

yes, this patch is needed. And in future i will add the RGB format settings.

> If you insist - I'll take it, but I'd add the "reset value"
> reasoning.

That would be great, thank you very much.

Best Regards,
Josh Wu

> Otherwise maybe just drop it?
>
> Thanks
> Guennadi
>
>> Currently only support YUV format from camera sensor.
>>
>> Signed-off-by: Josh Wu <josh.wu@atmel.com>
>> ---
>>
>>   drivers/media/platform/soc_camera/atmel-isi.c | 20 +++++++-------------
>>   1 file changed, 7 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/media/platform/soc_camera/atmel-isi.c b/drivers/media/platform/soc_camera/atmel-isi.c
>> index 9070172..8bc40ca 100644
>> --- a/drivers/media/platform/soc_camera/atmel-isi.c
>> +++ b/drivers/media/platform/soc_camera/atmel-isi.c
>> @@ -105,24 +105,25 @@ static u32 isi_readl(struct atmel_isi *isi, u32 reg)
>>   static int configure_geometry(struct atmel_isi *isi, u32 width,
>>   			u32 height, u32 code)
>>   {
>> -	u32 cfg2, cr;
>> +	u32 cfg2;
>>   
>> +	/* According to sensor's output format to set cfg2 */
>>   	switch (code) {
>>   	/* YUV, including grey */
>>   	case MEDIA_BUS_FMT_Y8_1X8:
>> -		cr = ISI_CFG2_GRAYSCALE;
>> +		cfg2 = ISI_CFG2_GRAYSCALE;
>>   		break;
>>   	case MEDIA_BUS_FMT_VYUY8_2X8:
>> -		cr = ISI_CFG2_YCC_SWAP_MODE_3;
>> +		cfg2 = ISI_CFG2_YCC_SWAP_MODE_3;
>>   		break;
>>   	case MEDIA_BUS_FMT_UYVY8_2X8:
>> -		cr = ISI_CFG2_YCC_SWAP_MODE_2;
>> +		cfg2 = ISI_CFG2_YCC_SWAP_MODE_2;
>>   		break;
>>   	case MEDIA_BUS_FMT_YVYU8_2X8:
>> -		cr = ISI_CFG2_YCC_SWAP_MODE_1;
>> +		cfg2 = ISI_CFG2_YCC_SWAP_MODE_1;
>>   		break;
>>   	case MEDIA_BUS_FMT_YUYV8_2X8:
>> -		cr = ISI_CFG2_YCC_SWAP_DEFAULT;
>> +		cfg2 = ISI_CFG2_YCC_SWAP_DEFAULT;
>>   		break;
>>   	/* RGB, TODO */
>>   	default:
>> @@ -130,17 +131,10 @@ static int configure_geometry(struct atmel_isi *isi, u32 width,
>>   	}
>>   
>>   	isi_writel(isi, ISI_CTRL, ISI_CTRL_DIS);
>> -
>> -	cfg2 = isi_readl(isi, ISI_CFG2);
>> -	/* Set YCC swap mode */
>> -	cfg2 &= ~ISI_CFG2_YCC_SWAP_MODE_MASK;
>> -	cfg2 |= cr;
>>   	/* Set width */
>> -	cfg2 &= ~(ISI_CFG2_IM_HSIZE_MASK);
>>   	cfg2 |= ((width - 1) << ISI_CFG2_IM_HSIZE_OFFSET) &
>>   			ISI_CFG2_IM_HSIZE_MASK;
>>   	/* Set height */
>> -	cfg2 &= ~(ISI_CFG2_IM_VSIZE_MASK);
>>   	cfg2 |= ((height - 1) << ISI_CFG2_IM_VSIZE_OFFSET)
>>   			& ISI_CFG2_IM_VSIZE_MASK;
>>   	isi_writel(isi, ISI_CFG2, cfg2);
>> -- 
>> 1.9.1
>>