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Thu, 10 Oct 2019 00:50:02 -0700 (PDT) MIME-Version: 1.0 References: <893c3b4f03266c9496137cc98ac2b1bd27f92c73.1570633189.git.vilhelm.gray@gmail.com> <20191009170917.GG32742@smile.fi.intel.com> In-Reply-To: From: Geert Uytterhoeven Date: Thu, 10 Oct 2019 09:49:51 +0200 Message-ID: Subject: Re: [PATCH v17 01/14] bitops: Introduce the for_each_set_clump8 macro To: Andy Shevchenko X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191010_005003_462392_DED432D6 X-CRM114-Status: GOOD ( 25.05 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch , Phil Reid , Arnd Bergmann , Bartosz Golaszewski , Linus Walleij , Linux PM mailing list , Rasmus Villemoes , William Breathitt Gray , morten.tiljeset@prevas.dk, Linux Kernel Mailing List , Masahiro Yamada , Lukas Wunner , "open list:GPIO SUBSYSTEM" , sean.nyekjaer@prevas.dk, Andrew Morton , Andy Shevchenko , linux-arm-kernel Content-Type: text/plain; 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 Hi Andy, 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: > > > > > > > > > > > > > > > > This macro iterates for each 8-bit 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_value8 and bitmap_set_value8 functions are introduced to > > > > > > > > respectively get and set an 8-bit value in a bitmap memory region. > > > > > > > > > > > > > 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. > > > > > > > > > > > > > +1 > > > > > > > > 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. > 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? Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel