On Thursday 12 December 2013 11:31 PM, Stephen Warren wrote:
On 12/12/2013 06:24 AM, Laxman Dewangan wrote:Add of_property_read_s32() to read the signed 32bit number 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;I may not be thinking straight today since I have a cold, but doesn't 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?
This is correct if all architecture follows the 2's complement for -Ve number representation.
If this is true then the patch will become more easy. -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
