linux-kernel - Re: [PATCH 0/5] gpiolib: Handle immutable irq

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Date:   Thu, 24 Feb 2022 17:40:43 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        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>,
        Thomas Gleixner <tglx@...utronix.de>,
        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 0/5] gpiolib: Handle immutable irq_chip structures

On Wed, Feb 23, 2022 at 03:44:00PM +0000, Marc Zyngier wrote:
> 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.
> 
> My current approach is to add a new irq_chip flag (IRQCHIP_IMMUTABLE)
> which does what it says on the tin: don't you dare writing there.
> Gpiolib is further updated not to install its own callbacks, and it
> becomes the responsibility of the driver to call into the gpiolib when
> required. This is similar to what we do for other subsystems such as
> PCI-MSI.
> 
> 3 drivers are updated to this new model: M1, QC and Tegra, as I
> actively use them (though Tegra is hosed at the moment), keeping a

Hosed in what way? Anything I can help with?

Thierry

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