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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Oct 10, 2019 at 09:49:51AM +0200, Geert Uytterhoeven wrote: > On Thu, Oct 10, 2019 at 9:42 AM Andy Shevchenko > wrote: > > On Thu, Oct 10, 2019 at 9:29 AM Geert Uytterhoeven wrote: > > > On Thu, Oct 10, 2019 at 7:49 AM Andy Shevchenko > > > wrote: > > > > On Thu, Oct 10, 2019 at 5:31 AM Masahiro Yamada > > > > wrote: > > > > > On Thu, Oct 10, 2019 at 3:54 AM Geert Uytterhoeven wrote: > > > > > > On Wed, Oct 9, 2019 at 7:09 PM Andy Shevchenko > > > > > > wrote: > > > > > > > On Thu, Oct 10, 2019 at 01:28:08AM +0900, Masahiro Yamada wrote: > > > > > > > > On Thu, Oct 10, 2019 at 12:27 AM William Breathitt Gray > > > > > > > > wrote: > > > > > > > > Why is the return type "unsigned long" where you know > > > > > > > > it return the 8-bit value ? > > > > > > > > > > > > > > Because bitmap API operates on unsigned long type. This is not only > > > > > > > consistency, but for sake of flexibility in case we would like to introduce > > > > > > > more calls like clump16 or so. > > > > > > > > > > > > TBH, that doesn't convince me: those functions explicitly take/return an > > > > > > 8-bit value, and have "8" in their name. The 8-bit value is never > > > > > > really related to, retrieved from, or stored in a full "unsigned long" > > > > > > element of a bitmap, only to/from/in a part (byte) of it. > > > > > > > > > > > > Following your rationale, all of iowrite{8,16,32,64}*() should take an > > > > > > "unsigned long" value, too. > > > > > > > > > > Using u8/u16/u32/u64 looks more consistent with other bitmap helpers. > > > > > > > > > > void bitmap_from_arr32(unsigned long *bitmap, const u32 *buf, unsigned > > > > > int nbits); > > > > > void bitmap_to_arr32(u32 *buf, const unsigned long *bitmap, unsigned int nbits); > > > > > static inline void bitmap_from_u64(unsigned long *dst, u64 mask); > > > > > > > > > > If you want to see more examples from other parts, > > > > > > > > Geert's and yours examples both are not related. They are about > > > > fixed-width properies when we know that is the part of protocol. > > > > Here we have no protocol which stricts us to the mentioned fixed-width types. > > > > > > Yes you have: they are functions to store/retrieve an 8-bit value from > > > the middle of the bitmap, which is reflected in their names ("clump8", > > > "value8"). > > > The input/output value is clearly separated from the actual bitmap, > > > which is referenced by the "unsigned long *". > > > > > > If you add new "value16" functions, they will be intended to store/retrieve > > > 16-bit values. > > > > And if I add 4-bit, 12-bit or 24-bit values, what should I use? > > Whatever is needed to store that? > I agree "unsigned long" is appropriate for a generic function to extract a > bit field of 1 to BITS_PER_LONG bits. > > > > Besides, if retrieving an 8-bit value requires passing an > > > "unsigned long *", the caller needs two variables: one unsigned long to > > > pass the address of, and one u8 to copy the returned value into. > > > > Why do you need a temporary variable? In some cases it might make > > sense, but in general simple cases I don't see what you may achieve > > with it. > > Because find_next_clump8() takes a pointer to store the output value. So does regmap_read(). 8 appeared there during review when it has been proposed to optimize to 8-bit clumps as most of the current users utilize it. The initial idea was to be bit-width agnostic. And with current API it's possible to easy convert to other formats later if we need. > > I looked at bitmap.h and see few functions may have benefited of > > actually eliminating a use of long -> u8 -> long conversion. > > > > Here is the question what we are mostly doing after we got a clump out > > of bitmap. > > If I call find_next_clump8() to extract a byte, I guess I want to process an u8 > aftwerwards? Some functions may expect a width-(semi-)dependent types, like regmap_write(). Yes, it's possible to supply u8 there and have an implicit type cast. -- With Best Regards, Andy Shevchenko _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel