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

From: Linus Walleij <linus.walleij@linaro.org>
To: Marc Zyngier <maz@kernel.org>
Cc: linux-kernel@vger.kernel.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>,
	Andy Shevchenko <andy.shevchenko@gmail.com>,
	 linux-gpio@vger.kernel.org, linux-tegra@vger.kernel.org,
	 linux-arm-kernel@lists.infradead.org,
	linux-arm-msm@vger.kernel.org,  kernel-team@android.com
Subject: Re: [PATCH v3 00/10] gpiolib: Handle immutable irq_chip structures
Date: Fri, 22 Apr 2022 23:24:22 +0200	[thread overview]
Message-ID: <CACRpkda3L_itpqcnPq6xDoJtNHt8NuvE1MZk1bCNR+u2KKUpBA@mail.gmail.com> (raw)
In-Reply-To: <20220419141846.598305-1-maz@kernel.org>

On Tue, Apr 19, 2022 at 4:19 PM Marc Zyngier <maz@kernel.org> 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.
>
> 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 to them.
> 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.
>
> 5 drivers are updated to this new model: M1, QC, Tegra, pl061 and AMD
> (as I actively use them) keeping a single irq_chip structure, marking
> it const, and exposing the new flag.
>
> Nothing breaks, the volume of change is small, the memory usage goes
> down and we have fewer callbacks that can be used as attack vectors.
> What's not to love?
>
> Since there wasn't any objection in the previous round of review, I'm
> going to take this series into -next to see if anything breaks at
> scale.

The series:
Acked-by: Linus Walleij <linus.walleij@linaro.org>

Bartosz: if you're happy with this can you apply it to an immutable branch
from v5.18-rc1 and merge that into the GPIO for-next and then I can also
pull that into pinctrl?

Yours,
Linus Walleij

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