On Tue, 22 Oct 2013, Sebastian Andrzej Siewior wrote: > On 08/07/2013 10:40 AM, Lee Jones wrote: > > On Mon, 05 Aug 2013, Zubair Lutfullah wrote: > > > >> Reg_cache variable is used to lock step enable register > >> from being accessed and written by both TSC and ADC > >> at the same time. > >> However, it isn't updated anywhere in the code at all. > >> > >> If both TSC and ADC are used, eventually 1FFFF is always > >> written enabling all 16 steps uselessly causing a mess. > >> > >> Patch fixes it by correcting the locks and updates the > >> variable by reading the step enable register > >> > >> Signed-off-by: Zubair Lutfullah <[email protected]> > >> --- > >> drivers/mfd/ti_am335x_tscadc.c | 4 ++-- > >> 1 file changed, 2 insertions(+), 2 deletions(-) > > > > Better that it comes from somewhere. > > I don't understand. All three functions are used before the patch has > been applied: > > $ git grep -l am335x_tsc_se_set > drivers/iio/adc/ti_am335x_adc.c > drivers/input/touchscreen/ti_am335x_tsc.c > drivers/mfd/ti_am335x_tscadc.c > > $ git grep -l am335x_tsc_se_clr > drivers/iio/adc/ti_am335x_adc.c > drivers/input/touchscreen/ti_am335x_tsc.c > drivers/mfd/ti_am335x_tscadc.c > > $ git grep -l am335x_tsc_se_update > drivers/iio/adc/ti_am335x_adc.c > drivers/input/touchscreen/ti_am335x_tsc.c > drivers/mfd/ti_am335x_tscadc.c > include/linux/mfd/ti_am335x_tscadc.h > > It has been initialized to 0 by time the mfd part was loaded and > updated via …_set() from both parts (TSC & ADC). The lock ensured that > we never lose or add bits due to a race. So I don't understand why we > end up with 0x1FFFF. > Could some please explain to me how this can happen? > > I added reg_se_cache to cache the content of REG_SE once and > synchronize it among TSC & ADC access. REG_SE is set to 0 by the HW > after "work" has been done. So you need to know the old value or TSC may > disable ADC and the other way around.
Yep, it's initialised as '0'. 12.5.1.15 STEPENABLE Register (offset = 54h) [reset = 0h] -- Lee Jones Linaro STMicroelectronics Landing Team Lead Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
