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 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. Another approach was to let gpiolib provide its own irq_chip structure and stack it, but: - only a few drivers are hierarchy aware - the diversity of interrupt flows makes it impractical I'd welcome comments on the approach. If deemed acceptable, there are another 300+ drivers to update! Not to mention the documentation. I appreciate that this is a lot of potential changes, but the current situation is messy. Note that these patches are on top of irqchip-next, which contains more constifying work. M. Marc Zyngier (5): gpio: Don't fiddle with irqchips marked as immutable gpio: Expose the gpiochip_irq_re[ql]res helpers pinctrl: apple-gpio: Make the irqchip immutable pinctrl: msmgpio: Make the irqchip immutable gpio: tegra186: Make the irqchip immutable drivers/gpio/gpio-tegra186.c | 33 ++++++++++++----- drivers/gpio/gpiolib.c | 13 +++++-- drivers/pinctrl/pinctrl-apple-gpio.c | 30 +++++++++------- drivers/pinctrl/qcom/pinctrl-msm.c | 53 +++++++++++++++++----------- include/linux/gpio/driver.h | 4 +++ include/linux/irq.h | 2 ++ kernel/irq/debugfs.c | 1 + 7 files changed, 91 insertions(+), 45 deletions(-) -- 2.30.2
