On Mon, May 04, 2020 at 02:41:09PM +0300, Andy Shevchenko wrote: > On Sun, May 03, 2020 at 04:38:36AM +0530, Syed Nayyar Waris wrote: > > 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 of any size but > > less than or equal to BITS_PER_LONG. The patchset utilizes the new macro > > in several 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. > > Looking into the last patches where we have examples I still do not see a > benefit of variadic clump sizes. power of 2 sizes would make sense (and be > optimized accordingly (64-bit, 32-bit). > > -- > With Best Regards, > Andy Shevchenko There is of course benefit in defining for_each_set_clump with clump sizes of powers of 2 (we can optimize for 32 and 64 bit sizes and avoid boundary checks that we know will not occur), but at the very least the variable size bitmap_set_value and bitmap_get_value provide significant benefit for the readability of the gpio-xilinx code: bitmap_set_value(old, state[0], 0, width[0]); bitmap_set_value(old, state[1], width[0], width[1]); ... state[0] = bitmap_get_value(new, 0, width[0]); state[1] = bitmap_get_value(new, width[0], width[1]); These lines are simple and clear to read: we know immediately what they do. But if we did not have bitmap_set_value/bitmap_get_value, we'd have to use several bitwise operations for each line; the obfuscation of the code would be an obvious hinderance here. William Breathitt Gray
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