linux-kernel - Re: [PATCH v3 00/10] gpiolib: Handle immutable irq

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Date:   Fri, 13 May 2022 10:43:29 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Thierry Reding <thierry.reding@...il.com>,
        Joey Gouly <joey.gouly@....com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Hector Martin <marcan@...can.st>,
        Sven Peter <sven@...npeter.dev>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Jeffrey Hugo <jeffrey.l.hugo@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Basavaraj Natikar <Basavaraj.Natikar@....com>,
        Shyam Sundar S K <Shyam-sundar.S-k@....com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        linux-arm-msm@...r.kernel.org,
        Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH v3 00/10] gpiolib: Handle immutable irq_chip structures

On Fri, May 13, 2022 at 12:18 AM Marc Zyngier <maz@...nel.org> wrote:
> On Thu, 12 May 2022 18:35:55 +0100,
> Andy Shevchenko <andy.shevchenko@...il.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. Also
/sys/kernel/irq rings a bell, but not sure if it's related.

-- 
With Best Regards,
Andy Shevchenko