On Tue, Oct 02, 2018 at 11:21:42AM +0300, Andy Shevchenko wrote: > On Tue, Oct 02, 2018 at 09:42:48AM +0200, Rasmus Villemoes wrote: > > On 2018-10-02 03:13, William Breathitt Gray wrote: > > > The cover letter says > > > > The clump_size argument can be an arbitrary number of bits and is not > > required to be a multiple of 2. > > > > by which I assume you mean "power of 2", but either way, the above code > > does not seem to take into account the case where bits_offset + > > clump_size straddles a word boundary, so it wouldn't work for a > > clump_size that does not divide BITS_PER_LONG. > > E.g. 3 bits in a clump? Hmm... > > Why would we need that? I mean some real use case? GPIOs in hardware may be routed to devices logically in groups of I/O lines, yet must still be accessed via the word-sized registers on the operating machine. For example, suppose a GPIO card is used to control a set of shower devices. The card supports 4 shower devices, each device controlled by 3 lines of I/O: enable, hot-cold selection, high-low pressure selection. In this case, a operating machine would still have to access the GPIO lines via the I/O registers (e.g. 8-bit port I/O); but with a macro handling a clump size of 3-bits, we can loop logically by each shower device which is much simpler from a driver perspective. William Breathitt Gray
