[PATCH 09/22] drm/i915: Create color management files

[Sharma, Shashank]

Regards
Shashank

On 10/10/2015 4:17 AM, Emil Velikov wrote:
> Hi Shashank,
>
> On 9 October 2015 at 20:28, Shashank Sharma <shashank.sharma at intel.com> wrote:
> [snip]
>> +
>> +/* Color management bit utilities */
>> +#define GET_BIT_MASK(n) ((1 << n) - 1)
>> +
>> +/* Read bits of a word from bit no. 'start'(lsb) till 'n' bits */
>> +#define GET_BITS(x, start, nbits) ((x >> start) & GET_BIT_MASK(nbits))
>> +
>> +/* Round off by adding 1 to the immediate lower bit */
>> +#define GET_BITS_ROUNDOFF(x, start, nbits) \
>> +       ((GET_BITS(x, start, (nbits + 1)) + 1) >> 1)
>> +
>> +/* Clear bits of a word from bit no. 'start' till nbits */
>> +#define CLEAR_BITS(x, start, nbits) ( \
>> +               x &= ~((GET_BIT_MASK(nbits) << start)))
>> +
>> +/* Write bit_pattern of no_bits bits in a target word */
>> +#define SET_BITS(target, bit_pattern, start_bit, no_bits) \
>> +               do { \
>> +                       CLEAR_BITS(target, start_bit, no_bits); \
>> +                       target |= (bit_pattern << start_bit);  \
>> +               } while (0)
> It feels suspicious that the kernel does not have macros for either
> one of these.
>
> I would invite you to take a look at include/linux/bitops.h and other
> kernel headers.
>
Thanks for pointing this out, but if you closely observe, these macros 
are well tested, and created for color management operations, which have 
specific requirements, like:
- pick 8 bits from 16th bit onwards, make them LSB, and give result: 
GET_BITS
- take these 8 bits and move to bit 17th of the word, clearing the 
existing ones: SET_BITS
For core register programming, this was required, so we created it. I 
would still have a look
at the existing ones which you pointed out to avoid any duplication, if 
they fall directly in the implementation, else I would like to continue 
with these.
> Regards,
> Emil
>