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bitops: introduce the for_each_set_clump macro
Patch series "Introduce the for_each_set_clump macro", v12. This patchset introduces a new generic version of for_each_set_clump. The previous version of for_each_set_clump8 used a fixed size 8-bit clump, but the new generic version can work with clump (n-bits) having size between 1 and BITS_PER_LONG inclusive. size less than 1 or more than BITS_PER_LONG causes undefined behaviour. The patchset utilizes the new macro in some GPIO drivers. The earlier 8-bit for_each_set_clump8 facilitated a for-loop syntax that iterates over a memory region entire groups of set bits at a time. For example, suppose you would like to iterate over a 32-bit integer 8 bits at a time, skipping over 8-bit groups with no set bit, where XXXXXXXX represents the current 8-bit group: Example: 10111110 00000000 11111111 00110011 First loop: 10111110 00000000 11111111 XXXXXXXX Second loop: 10111110 00000000 XXXXXXXX 00110011 Third loop: XXXXXXXX 00000000 11111111 00110011 Each iteration of the loop returns the next 8-bit group that has at least one set bit. But with the new for_each_set_clump the clump size can be different from 8 bits. Moreover, the clump can be split at word boundary in situations where word size is not multiple of clump size. Following are examples showing the working of new macro for clump sizes of 24 bits and 6 bits. Example 1: clump size: 24 bits, Number of clumps (or ports): 10 bitmap stores the bit information from where successive clumps are retrieved. /* bitmap memory region */ 0x00aa0000ff000000; /* Most significant bits */ 0xaaaaaa0000ff0000; 0x000000aa000000aa; 0xbbbbabcdeffedcba; /* Least significant bits */ Different iterations of for_each_set_clump:- 'offset' is the bit position and 'clump' is the 24 bit clump from the above bitmap. Iteration first: offset: 0 clump: 0xfedcba Iteration second: offset: 24 clump: 0xabcdef Iteration third: offset: 48 clump: 0xaabbbb Iteration fourth: offset: 96 clump: 0xaa Iteration fifth: offset: 144 clump: 0xff Iteration sixth: offset: 168 clump: 0xaaaaaa Iteration seventh: offset: 216 clump: 0xff Loop breaks because in the end the remaining bits (0x00aa) size was less than clump size of 24 bits. In above example it can be seen that in iteration third, the 24 bit clump that was retrieved was split between bitmap[0] and bitmap[1]. This example also shows that 24 bit zeroes if present in between, were skipped (preserving the previous for_each_set_macro8 behaviour). Example 2: clump size = 6 bits, Number of clumps (or ports) = 3. /* bitmap memory region */ 0x00aa0000ff000000; /* Most significant bits */ 0xaaaaaa0000ff0000; 0x0f00000000000000; 0x0000000000000ac0; /* Least significant bits */ Different iterations of for_each_set_clump: 'offset' is the bit position and 'clump' is the 6 bit clump from the above bitmap. Iteration first: offset: 6 clump: 0x2b Loop breaks because 6 * 3 = 18 bits traversed in bitmap. Here 6 * 3 is clump size * no. of clumps. This patch (of 4): This macro iterates for each group of bits (clump) with set bits, within a bitmap memory region. For each iteration, "start" is set to the bit offset of the found clump, while the respective clump value is stored to the location pointed by "clump". Additionally, the bitmap_get_value() and bitmap_set_value() functions are introduced to respectively get and set a value of n-bits in a bitmap memory region. The n-bits can have any size from 1 to BITS_PER_LONG. size less than 1 or more than BITS_PER_LONG causes undefined behaviour. Moreover, during setting value of n-bit in bitmap, if a situation arise that the width of next n-bit is exceeding the word boundary, then it will divide itself such that some portion of it is stored in that word, while the remaining portion is stored in the next higher word. Similar situation occurs while retrieving the value from bitmap. Link: https://lkml.kernel.org/r/cover.1603055402.git.syednwaris@gmail.com Link: https://lkml.kernel.org/r/199b749c404450d1acb667e629ec4da37f44b60c.1603055402.git.syednwaris@gmail.com Signed-off-by: Syed Nayyar Waris <syednwaris@gmail.com> Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Linus Walleij <linus.walleij@linaro.org> Cc: Bartosz Golaszewski <bgolaszewski@baylibre.com> Cc: Michal Simek <michal.simek@xilinx.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
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