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Wed, 09 Oct 2019 23:29:29 -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 08:29:17 +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-20191009_232932_283509_9E46ABF8 X-CRM114-Status: GOOD ( 21.35 ) 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 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. 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. > So, I can tell an opposite, your arguments didn't convince me. > > Imagine the function which does an or / and / xor operation on bitmap. > Now, when I supply unsigned long, I will see > operations on one type in _one_ function independently of the size. > Your proposal will make an unneded churn. Depends on what kind of value you will use to do the logical operation with the bitmap: - Full bitmap => unsigned long * + size, - Single bitmap "word" => unsigned long, - 8-bit value => u8, - 16-bit value => u16 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