Hi Phil, On Wed, Jul 10, 2019 at 4:00 AM Phil Reid <pr...@electromag.com.au> wrote: > On 6/07/2019 00:05, Geert Uytterhoeven wrote: > > GPIO controllers are exported to userspace using /dev/gpiochip* > > character devices. Access control to these devices is provided by > > standard UNIX file system permissions, on an all-or-nothing basis: > > either a GPIO controller is accessible for a user, or it is not. > > Currently no mechanism exists to control access to individual GPIOs. > > > > Hence add a virtual GPIO driver to aggregate existing GPIOs (up to 32), > > and expose them as a new gpiochip. This is useful for implementing > > access control, and assigning a set of GPIOs to a specific user. > > Furthermore, it would simplify and harden exporting GPIOs to a virtual > > machine, as the VM can just grab the full virtual GPIO controller, and > > no longer needs to care about which GPIOs to grab and which not, > > reducing the attack surface. > > > > Virtual GPIO controllers are instantiated by writing to the "new_device" > > attribute file in sysfs: > > > > $ echo "<gpiochipA> <gpioA1> [<gpioA2> ...]" > > "[, <gpiochipB> <gpioB1> [<gpioB2> ...]] ...]" > > > /sys/bus/platform/drivers/gpio-virt-agg/new_device > > > > Likewise, virtual GPIO controllers can be destroyed after use: > > > > $ echo gpio-virt-agg.<N> \ > > > /sys/bus/platform/drivers/gpio-virt-agg/delete_device > > > > Nice. > This provides similar functionality to the "gpio inverter" driver currently > on the list. > Other than being just a buffer.
Indeed, both drivers forward GPIO calls, but the gpio inverter modifies some parameters passed. The way the drivers obtain references to GPIOs is different, though: the inverter driver obtains a fixed description from DT, while the virtual aggregator receives the description at runtime, from sysfs. But perhaps both drivers could share some code? > Would it be possible to do the lookup via line names? Doesn't the fact that a GPIO has a line name means that it is in use, and thus cannot be aggregated and exported to another user? Thanks! Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds