[RFC PATCH 1/2] of: Add a variant of of_device_is_compatible() that can be build time culled

[Daniel Palmer <daniel@thingy.jp>]

In a lot of places we are using of_device_is_compatible() to check for quirks
etc that are simply not possible on some targets, i.e. a piece of hardware
that needs special handling is only on one specific ARM machine and your
target isn't even ARM.

Add of_device_is_possible_and_compatible() that also takes a Kconfig
symbol and checks if that is enabled before calling of_device_is_compatible().

The Kconfig symbol is build time constant and the compiler should
remove the call to of_device_is_compatible() if it is unneeded and also
remove the data for the compatible string.

Another merit of this is that in places were we are checking for quirks
outside of drivers themselves, i.e. in the gpio and spi subsystems where
some legacy devicetree handling is being handled for specific devices
is in the core code, when the drivers that need the quirks are removed
their Kconfig symbol should also be removed and it'll be easier to spot
that the quirk handling can also go.

Signed-off-by: Daniel Palmer <daniel@thingy.jp>
---
 include/linux/of.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/of.h b/include/linux/of.h
index 9bbdcf25a2b4..70be20b0be22 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -358,6 +358,8 @@ extern int of_property_read_string_helper(const struct device_node *np,
 					      const char **out_strs, size_t sz, int index);
 extern int of_device_is_compatible(const struct device_node *device,
 				   const char *);
+#define of_device_is_possible_and_compatible(symbol, device, string) \
+	(IS_ENABLED(symbol) && of_device_is_compatible(device, string))
 extern int of_device_compatible_match(const struct device_node *device,
 				      const char *const *compat);
 extern bool of_device_is_available(const struct device_node *device);
-- 
2.51.0