Re: [PATCH v17 01/14] bitops: Introduce the for_each_set_clump8 macro

From: Masahiro Yamada <yamada.masahiro@socionext.com>
To: Geert Uytterhoeven <geert@linux-m68k.org>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	William Breathitt Gray <vilhelm.gray@gmail.com>
Cc: linux-arch <linux-arch@vger.kernel.org>,
	Arnd Bergmann <arnd@arndb.de>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
	Linus Walleij <linus.walleij@linaro.org>,
	Linux PM mailing list <linux-pm@vger.kernel.org>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	morten.tiljeset@prevas.dk, sean.nyekjaer@prevas.dk,
	Bartosz Golaszewski <bgolaszewski@baylibre.com>,
	Lukas Wunner <lukas@wunner.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Phil Reid <preid@electromag.com.au>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v17 01/14] bitops: Introduce the for_each_set_clump8 macro
Date: Thu, 10 Oct 2019 11:28:50 +0900	[thread overview]
Message-ID: <CAK7LNASVdqU_6+_iinWStb9ALqLw494pnZKr46fLW+WJ9nUo6A@mail.gmail.com> (raw)
In-Reply-To: <CAMuHMdXyyrL4ibKvjMV6r8TuxpmK73=JxsWNEfcRk1NjwsnOjA@mail.gmail.com>

On Thu, Oct 10, 2019 at 3:54 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>
> Hi Andy,
>
> On Wed, Oct 9, 2019 at 7:09 PM Andy Shevchenko
> <andriy.shevchenko@linux.intel.com> 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
> > > <vilhelm.gray@gmail.com> 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,

int of_property_read_u8(const struct device_node *np,
                        const char *propname,
                        u8 *out_value)

int of_property_read_u16(const struct device_node *np,
                         const char *propname,
                         u16 *out_value)

-- 
Best Regards
Masahiro Yamada

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