linux-kernel - Re: [PATCH V2 02/15] sh: Eliminate unused irq_reg

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Date:	Thu, 30 Oct 2014 08:25:03 -0700
From:	Kevin Cernekee <cernekee@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Florian Fainelli <f.fainelli@...il.com>,
	Jason Cooper <jason@...edaemon.net>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Paul Mundt <lethal@...ux-sh.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Maxime Bizon <mbizon@...ebox.fr>,
	Jonas Gorski <jogo@...nwrt.org>,
	Linux MIPS Mailing List <linux-mips@...ux-mips.org>
Subject: Re: [PATCH V2 02/15] sh: Eliminate unused irq_reg_{readl,writel} accessors

On Thu, Oct 30, 2014 at 3:48 AM, Arnd Bergmann <arnd@...db.de> wrote:
> On Thursday 30 October 2014 11:43:00 Thomas Gleixner wrote:
>> On Thu, 30 Oct 2014, Arnd Bergmann wrote:
>>
>> > On Wednesday 29 October 2014 19:17:55 Kevin Cernekee wrote:
>> > > Defining these macros way down in arch/sh/.../irq.c doesn't cause
>> > > kernel/irq/generic-chip.c to use them.  As far as I can tell this code
>> > > has no effect.
>> > >
>> > > Signed-off-by: Kevin Cernekee <cernekee@...il.com>
>> >
>> > Actually it overrides the 32-bit accessors with 16-bit accessors,
>> > which does seem intentional and certainly has an effect.
>>
>> Not really. Neither arch/sh/boards/mach-se/7343/irq.c nor
>> arch/sh/boards/mach-se/7722/irq.c actually use
>> irq_reg_readl/writel. They simply define it.
>
> Ah, that makes things easier. I looked at the commits that introduced
> them, and even then they were unused. Probably an artifact from an
> earlier version of the patch which did not get merged.

I suspect that the intention was to put them into the machine's
<irq.h> so that generic-chip.c would pick them up.  The sh irq.c files
do call ioread16/iowrite16 themselves, and like bcm7120-l2, they
utilize irq_gc_mask_{set,clr}_bit from generic-chip.c.

This may be something for the maintainers (Paul?) to double-check, but
if the submission worked as-is, maybe overriding the I/O accessors
wasn't actually needed.  Or maybe there are subtle and unfortunate
side effects on adjacent registers.
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