Re: [PATCH v2 00/10] gpiolib: Handle immutable irq_chip structures

[Andy Shevchenko <andy.shevchenko@xxxxxxxxx>]

On Wed, Apr 6, 2022 at 2:06 PM Marc Zyngier <maz@xxxxxxxxxx> wrote:
>
> This is a followup from [1].
>
> 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?

Reviewed-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
for the patches 1-3,9 and 10 after clarifying one example case.

> * From v1 [1]:
>   - pl061 and AMD drivers converted
>   - New helpers to keep the changes small
>   - New warning for non-converted drivers
>   - Documentation and TODO updates
>
> [1] https://lore.kernel.org/r/20220223154405.54912-1-maz@xxxxxxxxxx
>
> Marc Zyngier (10):
>   gpio: Don't fiddle with irqchips marked as immutable
>   gpio: Expose the gpiochip_irq_re[ql]res helpers
>   gpio: Add helpers to ease the transition towards immutable irq_chip
>   gpio: tegra186: Make the irqchip immutable
>   gpio: pl061: Make the irqchip immutable
>   pinctrl: apple-gpio: Make the irqchip immutable
>   pinctrl: msmgpio: Make the irqchip immutable
>   pinctrl: amd: Make the irqchip immutable
>   gpio: Update TODO to mention immutable irq_chip structures
>   Documentation: Update the recommended pattern for GPIO irqchips
>
>  Documentation/driver-api/gpio/driver.rst | 175 ++++++++++++++++++-----
>  drivers/gpio/TODO                        |  19 +++
>  drivers/gpio/gpio-pl061.c                |  32 +++--
>  drivers/gpio/gpio-tegra186.c             |  32 +++--
>  drivers/gpio/gpiolib.c                   |  13 +-
>  drivers/pinctrl/pinctrl-amd.c            |  11 +-
>  drivers/pinctrl/pinctrl-apple-gpio.c     |  29 ++--
>  drivers/pinctrl/qcom/pinctrl-msm.c       |  53 ++++---
>  include/linux/gpio/driver.h              |  16 +++
>  include/linux/irq.h                      |   2 +
>  kernel/irq/debugfs.c                     |   1 +
>  11 files changed, 293 insertions(+), 90 deletions(-)
>
> --
> 2.34.1
>


-- 
With Best Regards,
Andy Shevchenko