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

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Message-ID: <87tu9umm3k.wl-maz@kernel.org>
Date:   Thu, 12 May 2022 23:18:07 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     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>,
        linux-gpio@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v3 00/10] gpiolib: Handle immutable irq_chip structures

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.

	M.

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