| Message ID | 1373789069-11604-2-git-send-email-josh.wu@atmel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Josh, On Sun, Jul 14, 2013 at 04:04:25PM +0800, Josh Wu wrote: > for example, if adc_clk is 20Mhz and start-up time set as larger than 215us. > then the calculation "st->startup_time * adc_clk_khz" will out of u32. > > In this patch, it will use khz unit for adc_clk, that avoids above problem. > > Signed-off-by: Josh Wu <josh.wu@atmel.com> Maybe we can have a slightly better commit log here, like: ------8<----------- iio: at91: Fix adc_clk overflow The adc_clk variable is currently defined using a 32-bits unsigned integer, which will overflow under some very valid range of operations. Such overflow will occur if, for example, the parent clock is set to a 20MHz frequency and the ADC startup time is larger than 215ns. To fix this, introduce an intermediate variable holding the clock rate in kHz. --------8<--------------- Or something like that. For the patch itself, I'm happy about it. You can add my Acked-by. Thanks! Maxime
Hi, Maxime On 7/15/2013 8:52 PM, Maxime Ripard wrote: > Hi Josh, > > On Sun, Jul 14, 2013 at 04:04:25PM +0800, Josh Wu wrote: >> for example, if adc_clk is 20Mhz and start-up time set as larger than 215us. >> then the calculation "st->startup_time * adc_clk_khz" will out of u32. >> >> In this patch, it will use khz unit for adc_clk, that avoids above problem. >> >> Signed-off-by: Josh Wu <josh.wu@atmel.com> > Maybe we can have a slightly better commit log here, like: > > ------8<----------- > iio: at91: Fix adc_clk overflow > > The adc_clk variable is currently defined using a 32-bits unsigned > integer, which will overflow under some very valid range of operations. > > Such overflow will occur if, for example, the parent clock is set to a > 20MHz frequency and the ADC startup time is larger than 215ns. > > To fix this, introduce an intermediate variable holding the clock rate > in kHz. > > --------8<--------------- > > Or something like that. > > For the patch itself, I'm happy about it. You can add my Acked-by. Thank you. Your commit log is better. I will fix the commit log base on your commit in next version. > > Thanks! > Maxime > Best Regards, Josh Wu
diff --git a/drivers/iio/adc/at91_adc.c b/drivers/iio/adc/at91_adc.c index e5b88d5..18bd54f 100644 --- a/drivers/iio/adc/at91_adc.c +++ b/drivers/iio/adc/at91_adc.c @@ -582,7 +582,7 @@ static const struct iio_info at91_adc_info = { static int at91_adc_probe(struct platform_device *pdev) { - unsigned int prsc, mstrclk, ticks, adc_clk, shtim; + unsigned int prsc, mstrclk, ticks, adc_clk, adc_clk_khz, shtim; int ret; struct iio_dev *idev; struct at91_adc_state *st; @@ -680,6 +680,7 @@ static int at91_adc_probe(struct platform_device *pdev) */ mstrclk = clk_get_rate(st->clk); adc_clk = clk_get_rate(st->adc_clk); + adc_clk_khz = adc_clk / 1000; prsc = (mstrclk / (2 * adc_clk)) - 1; if (!st->startup_time) { @@ -693,15 +694,15 @@ static int at91_adc_probe(struct platform_device *pdev) * defined in the electrical characteristics of the board, divided by 8. * The formula thus is : Startup Time = (ticks + 1) * 8 / ADC Clock */ - ticks = round_up((st->startup_time * adc_clk / - 1000000) - 1, 8) / 8; + ticks = round_up((st->startup_time * adc_clk_khz / + 1000) - 1, 8) / 8; /* * a minimal Sample and Hold Time is necessary for the ADC to guarantee * the best converted final value between two channels selection * The formula thus is : Sample and Hold Time = (shtim + 1) / ADCClock */ - shtim = round_up((st->sample_hold_time * adc_clk / - 1000000) - 1, 1); + shtim = round_up((st->sample_hold_time * adc_clk_khz / + 1000) - 1, 1); reg = AT91_ADC_PRESCAL_(prsc) & AT91_ADC_PRESCAL; reg |= AT91_ADC_STARTUP_(ticks) & AT91_ADC_STARTUP;
for example, if adc_clk is 20Mhz and start-up time set as larger than 215us. then the calculation "st->startup_time * adc_clk_khz" will out of u32. In this patch, it will use khz unit for adc_clk, that avoids above problem. Signed-off-by: Josh Wu <josh.wu@atmel.com> --- drivers/iio/adc/at91_adc.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-)