On 12/12/2013 06:24 AM, Laxman Dewangan wrote:Add of_property_read_s32() to read the signed 32bit numberI may not be thinking straight today since I have a cold, but doesn't
from dt property value. This supports to pass the -ve numbers
from dt. Use 2's complement method for represnting negative number
and passed as u32 from dts. When reading back the value, again
converted to 2's complement if msb shows as 1.
diff --git a/include/linux/of.h b/include/linux/of.h
+static inline int of_property_read_s32(const struct device_node *np,
+ const char *propname,
+ s32 *out_value)
+{
+ u32 val;
+ int ret;
+
+ ret = of_property_read_u32(np, propname, &val);
+ if (ret < 0)
+ return ret;
+
+ /* 2's complement if MSB is 1 */
+ *out_value = (val & 0x80000000U) ? -((val ^ 0xFFFFFFFFU) + 1) : val;
patch 2/2 encode negative values as 2's complement, and an s32 variable
in the kernel is also encoded as 2's complement, so all you need here is
a cast:
*out_value = (s32)val;
... since the cast doesn't change the binary representation?