[PATCH v3 1/6] iio: at91: fix adc_clk overflow

[jic23@kernel.org (Jonathan Cameron)]

On 08/27/13 12:28, Josh Wu wrote:
> 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.
> 
> Signed-off-by: Josh Wu <josh.wu@atmel.com>
> Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Applied to the fixes-togreg branch of iio.git

Please in future separate out new stuff and fixes into separate series.
I tend to leave large series to review when I have time to do the whole
thing whereas little fixes in theory at least get picked up fast.

Thanks,

Jonathan
> ---
> v1 --> v2:
>   refined the commit message.
> 
>  drivers/iio/adc/at91_adc.c |   11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/iio/adc/at91_adc.c b/drivers/iio/adc/at91_adc.c
> index b6db6a0..9cf8ab5 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;
>