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. In tree (staging-next) I see that reg_se_cache ended being pointless. am335x_tsc_se_update() is no longer used from TSC or ADC. Only the _set() and _clr() functions are used which (both) read back the content of the REG_SE register before calling am335x_tsc_se_update(). That makes me think that we might cut of one part by accident. On the other hand Zubair said that he tested using ADC & TSC at the same time and it worked. So I have to double check if the HW really resets the content back to zero or not; maybe there is another explanation :) One thing that is an issue is that now the _set() function is using the lock without disabling interrupts and is called from non-IRQ (tiadc_read_raw()) and IRQ (titsc_irq()) context which might lead to deadlock. I'm going to send a patch for this. > Applied, thanks. Sebastian -- 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/
