Hi Guenter, Guenter Roeck wrote: > On Tue, Dec 18, 2012 at 04:03:41PM +0100, Juergen Beisert wrote: > > commit 263a523d18bca306016d75f5c8d5c57c37fe52fb changes the code of > > DIV_ROUND_CLOSEST in include/linux/kernel.h to fix a compile time > > warning. > > > > But now feeding in a zero into this macro results into 4198403. Tested > > with gcc 4.4.3 and 4.7.2, on arch x86 and ARM. > > > > I can reproduce this behaviour, when my ADC delivers a '0' value in the > > driver drivers/hwmon/s3c-hwmon.c in function s3c_hwmon_ch_show() with a > > current 3.7.1 kernel. The value is correct again, when the ADC delivers > > at least a '1'. > > > > Any ideas how to fix it correctly? > > Odd one. I ran the macro through a large number of values and divisors as > well as various optimization options, with different compilers, and always > get correct results. > > What are your compile options, and what are the channel multiplier and > dividers set to ?
Refer the lines 177 to 182 in drivers/hwmon/s3c-hwmon.c. "cfg->mult" is '3300' in my case, and "cfg->div" is '1023'. And whenever s3c_hwmon_read_ch() returns '0' line 184 returns '4198403' since Linux-3.6. checked with my gcc-4.6.2 cross compiler for Linux-3.6 and with gcc-4.6.2 for Linux-3.7. I did a quick test with this macro on my host with gcc-4.4.3 and a simple userland program and surprise, surprise: result = DIV_ROUND_CLOSEST(0, 1023); works as expected (result is 0), but int x = 0; unsigned y = 1023; result = DIV_ROUND_CLOSEST(x, y); gives me result = 4198403! Strange. Regards, Juergen -- Pengutronix e.K. | Juergen Beisert | Linux Solutions for Science and Industry | http://www.pengutronix.de/ | -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
