On Sat, Jan 23, 2021 at 2:52 PM Linus Walleij <[email protected]> wrote: > > On Fri, Jan 22, 2021 at 8:36 PM Saravana Kannan <[email protected]> wrote: > > > There are multiple instances of GPIO device tree nodes of the form: > > > > foo { > > compatible = "acme,foo"; > > ... > > > > gpio0: gpio0@xxxxxxxx { > > compatible = "acme,bar"; > > ... > > gpio-controller; > > }; > > > > gpio1: gpio1@xxxxxxxx { > > compatible = "acme,bar"; > > ... > > gpio-controller; > > }; > > > > ... > > } > > > > bazz { > > my-gpios = <&gpio0 ...>; > > } > > > > Case 1: The driver for "foo" populates struct device for these gpio* > > nodes and then probes them using a driver that binds with "acme,bar". > > This driver for "acme,bar" then registers the gpio* nodes with gpiolib. > > This lines up with how DT nodes with the "compatible" property are > > typically converted to struct devices and then registered with driver > > core to probe them. This also allows the gpio* devices to hook into all > > the driver core capabilities like runtime PM, probe deferral, > > suspend/resume ordering, device links, etc. > > > > Case 2: The driver for "foo" doesn't populate struct devices for these > > gpio* nodes before registering them with gpiolib. Instead it just loops > > through its child nodes and directly registers the gpio* nodes with > > gpiolib. > > > > Drivers that follow case 2 cause problems with fw_devlink=on. This is > > because fw_devlink will prevent bazz from probing until there's a struct > > device that has gpio0 as its fwnode (because bazz lists gpio0 as a GPIO > > supplier). Once the struct device is available, fw_devlink will create a > > device link with gpio0 device as the supplier and bazz device as the > > consumer. After this point, since the gpio0 device will never bind to a > > driver, the device link will prevent bazz device from ever probing. > > > > Finding and refactoring all the instances of drivers that follow case 2 > > will cause a lot of code churn and it is not something that can be done > > in one shot. In some instances it might not even be possible to refactor > > them cleanly. Examples of such instances are [1] [2]. > > > > This patch works around this problem and avoids all the code churn by > > simply setting the fwnode of the gpio_device and creating a stub driver > > to bind to the gpio_device. This allows all the consumers to continue > > probing when the driver follows case 2. > > > > [1] - https://lore.kernel.org/lkml/[email protected]/ > > [2] - > > https://lore.kernel.org/lkml/[email protected]/ > > Cc: Marc Zyngier <[email protected]> > > Cc: Jisheng Zhang <[email protected]> > > Cc: Kever Yang <[email protected]> > > Fixes: e590474768f1 ("driver core: Set fw_devlink=on by default") > > Signed-off-by: Saravana Kannan <[email protected]> > > This v5 version is a beauty!
Lol, thanks. > Reviewed-by: Linus Walleij <[email protected]> Considering the "Fixes" is only in driver-core-next, should this go through driver-core? -Saravana
