include/linux/bcd.h: provide bcd_is_valid() helper

bcd2bin(0x0A) happily returns 10, despite this being an invalid BCD
value. RTC drivers converting possibly corrupted BCD timestamps might
want to validate their input before calling bcd2bin().

Provide a macro to do so. Unlike bcd2bin and bin2bcd, out-of-line
versions are not implemented. Should the macro experience enough use,
this can be retrofitted.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Link: https://lore.kernel.org/r/20221123095527.2771434-2-s.hauer@pengutronix.de
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

diff --git a/include/linux/bcd.h b/include/linux/bcd.h
index 118bea3..abbc814 100644 (file)
--- a/include/linux/bcd.h
+++ b/include/linux/bcd.h
@@ -14,8 +14,12 @@
                const_bin2bcd(x) :                      \
                _bin2bcd(x))
 
+#define bcd_is_valid(x)                                        \
+               const_bcd_is_valid(x)
+
 #define const_bcd2bin(x)       (((x) & 0x0f) + ((x) >> 4) * 10)
 #define const_bin2bcd(x)       ((((x) / 10) << 4) + (x) % 10)
+#define const_bcd_is_valid(x)  (((x) & 0x0f) < 10 && ((x) >> 4) < 10)
 
 unsigned _bcd2bin(unsigned char val) __attribute_const__;
 unsigned char _bin2bcd(unsigned val) __attribute_const__;