On Thu, Apr 19, 2018 at 12:14:04PM +0900, Masahiro Yamada wrote:
The syscon implementation in U-Boot is different from that in Linux. Thus, DT files imported from Linux do not work for U-Boot.
In U-Boot driver model, each node is bound to a dedicated driver that is the most compatible to it. This design gets along with the concept of DT, and the syscon in Linux originally worked like that.
However, Linux commit bdb0066df96e ("mfd: syscon: Decouple syscon interface from platform devices") changed the behavior because it is useful to let a device bind to another driver, but still work as a syscon provider.
That change had happened before U-Boot initially supported the syscon driver by commit 6f98b7504f70 ("dm: Add support for generic system controllers (syscon)"). So, the U-Boot's syscon works differently from the beginning. I'd say this is mis-implementation given that DT is not oriented to a particular project, but Linux is the canon of DT in practice.
The problem typically arises in the combination of "syscon" and "simple-mfd" compatibles.
In Linux, they are orthogonal, i.e., the order between "syscon" and "simple-mfd" does not matter at all.
Assume the following compatible.
compatible = "foo,bar-syscon", "syscon", "simple-mfd";
In U-Boot, this device node is bound to the syscon driver (driver/core/syscon-uclass.c) since the "syscon" is found to be the most compatible. Then, syscon_get_regmap() succeeds.
However,
compatible = "foo,bar-syscon", "simple-mfd", "syscon";
does not work because this node is bound to the simple-bus driver (drivers/core/simple-bus.c) in favor of "simple-mfd" compatible. The compatible string "syscon" is just dismissed.
Moreover,
compatible = "foo,bar-syscon", "syscon";
works like the first case because the syscon driver populates the child devices. This is wrong because populating children is the job of "simple-mfd" (or "simple-bus").
This commit ports syscon_node_to_regmap() from Linux. This API does not require the given node to be bound to a driver in any way.
Reported-by: Kunihiko Hayashi hayashi.kunihiko@socionext.com Signed-off-by: Masahiro Yamada yamada.masahiro@socionext.com
Applied to u-boot/master, thanks!