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From: William Breathitt Gray <vilhelm.gray@gmail.com>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	linus.walleij@linaro.org, akpm@linux-foundation.org,
	linux-gpio@vger.kernel.org, linux-arch@vger.kernel.org,
	linux-kernel@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>
Subject: Re: [RESEND PATCH v4 1/8] bitops: Introduce the for_each_set_clump macro
Date: Thu, 4 Oct 2018 19:30:28 +0900	[thread overview]
Message-ID: <20181004103028.GA4779@icarus> (raw)
In-Reply-To: <20181002082142.GC15943@smile.fi.intel.com>

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

  parent reply	other threads:[~2018-10-04 10:30 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-02  1:12 [RESEND PATCH v4 0/8] Introduce the for_each_set_clump macro William Breathitt Gray
2018-10-02  1:13 ` [RESEND PATCH v4 1/8] bitops: " William Breathitt Gray
2018-10-02  7:42   ` Rasmus Villemoes
2018-10-02  8:21     ` Andy Shevchenko
2018-10-03 11:48       ` Andy Shevchenko
2018-10-04 10:36         ` William Breathitt Gray
2018-10-04 12:10           ` Andy Shevchenko
2018-10-04 10:30       ` William Breathitt Gray [this message]
2018-10-04 10:03     ` William Breathitt Gray
2018-10-02  1:14 ` [RESEND PATCH v4 2/8] lib/test_bitmap.c: Add for_each_set_clump test cases William Breathitt Gray
2018-10-02  1:14 ` [RESEND PATCH v4 3/8] gpio: 104-dio-48e: Utilize for_each_set_clump macro William Breathitt Gray
2018-10-02  7:00   ` Rasmus Villemoes
2018-10-14  4:19     ` William Breathitt Gray
2018-10-15 11:59       ` Rasmus Villemoes
2018-10-17  1:54         ` William Breathitt Gray
2018-10-02  1:15 ` [RESEND PATCH v4 4/8] gpio: 104-idi-48: " William Breathitt Gray
2018-10-02  1:15 ` [RESEND PATCH v4 5/8] gpio: gpio-mm: " William Breathitt Gray
2018-10-02  1:15 ` [RESEND PATCH v4 6/8] gpio: ws16c48: " William Breathitt Gray
2018-10-02  1:16 ` [RESEND PATCH v4 7/8] gpio: pci-idio-16: " William Breathitt Gray
2018-10-02  1:16 ` [RESEND PATCH v4 8/8] gpio: pcie-idio-24: " William Breathitt Gray

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