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

Marc Zyngier
2022-04-19T14:19:22Z

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.

Thanks,

M.

* From v2 [2]:
- Fixed documentation
- Collected RBs, with thanks

* 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@kernel.org
[2] https://lore.kernel.org/r/20220405135444.199295-1-maz@kernel.org

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