Re: [PATCH v3 00/10] gpiolib: Handle immutable irq_chip structures

From: Marc Zyngier <maz@kernel.org>
To: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linus Walleij <linus.walleij@linaro.org>,
	Bartosz Golaszewski <brgl@bgdev.pl>,
	Thierry Reding <thierry.reding@gmail.com>,
	Joey Gouly <joey.gouly@arm.com>,
	Jonathan Hunter <jonathanh@nvidia.com>,
	Hector Martin <marcan@marcan.st>, Sven Peter <sven@svenpeter.dev>,
	Alyssa Rosenzweig <alyssa@rosenzweig.io>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	Andy Gross <agross@kernel.org>,
	Jeffrey Hugo <jeffrey.l.hugo@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Basavaraj Natikar <Basavaraj.Natikar@amd.com>,
	Shyam Sundar S K <Shyam-sundar.S-k@amd.com>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
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	Android Kernel Team <kernel-team@android.com>
Subject: Re: [PATCH v3 00/10] gpiolib: Handle immutable irq_chip structures
Date: Fri, 13 May 2022 09:51:53 +0100	[thread overview]
Message-ID: <87tu9t6cie.wl-maz@kernel.org> (raw)
In-Reply-To: <CAHp75VfKMEcr1U=YQFfDRCpU=2LE78c76fSsAOFTWZHaswdiwg@mail.gmail.com>

On Fri, 13 May 2022 09:43:29 +0100,
Andy Shevchenko <andy.shevchenko@gmail.com> wrote:
> 
> On Fri, May 13, 2022 at 12:18 AM Marc Zyngier <maz@kernel.org> wrote:
> > On Thu, 12 May 2022 18:35:55 +0100,
> > Andy Shevchenko <andy.shevchenko@gmail.com> wrote:
> > >
> > > On Thu, May 12, 2022 at 08:08:28PM +0300, Andy Shevchenko wrote:
> > > > On Tue, Apr 19, 2022 at 03:18:36PM +0100, Marc Zyngier wrote:
> > > > > This is a followup from [2].
> > > > >
> > > > > I recently realised that the gpiolib play ugly tricks on the
> > > > > unsuspecting irq_chip structures by patching the callbacks.
> > > > >
> > > > > Not only this breaks when an irq_chip structure is made const (which
> > > > > really should be the default case), but it also forces this structure
> > > > > to be copied at nauseam for each instance of the GPIO block, which is
> > > > > a waste of memory.
> > > >
> > > > Is this brings us to the issue with IRQ chip name?
> > > >
> > > > The use case in my mind is the following:
> > > > 1) we have two or more GPIO chips that supports IRQ;
> > > > 2) the user registers two IRQs of the same (by number) pin on different chips;
> > > > 3) cat /proc/interrupt will show 'my_gpio_chip XX', where XX is the number.
> > > >
> > > > So, do I understand correct current state of affairs?
> > > >
> > > > If so, we have to fix this to have any kind of ID added to the chip name that
> > > > we can map /proc/interrupts output correctly.
> > >
> > > Hmm... Some drivers are using static names, some -- dynamically
> > > prepared (one way or another). Either way I think the ID is good to
> > > have if we still miss it.
> >
> > No, this is a terrible idea. /proc/interrupts gives you a hint of
> > which driver/subsystem deals with the interrupt. This isn't a source
> > of topological information. /sys/kernel/debug/irq has all the
> > information you can dream of, and much more. Just make use of it.
> 
> Okay, so IIUC the mapping is that: I got a vIRQ number from
> /proc/interrupts, but then I have to mount debugfs and look into it
> for a detailed answer of which chip/domain this vIRQ belongs to.

Normal users shouldn't care about irqdomains. If you are developing,
you already have debugfs enabled and mounted on your system.

> Also /sys/kernel/irq rings a bell, but not sure if it's related.

This is the same thing as /proc/interrupt, just dumped with a
different format.

	M.

-- 
Without deviation from the norm, progress is not possible.