On Sun, Sep 05, 2021 at 07:47:08PM +0200, Ansuel Smith wrote:
> The function can loop and lock the system if for whatever reason the bit
> for the target sensor is NEVER valid. This is the case if a sensor is
> disabled by the factory and the valid bit is never reported as actually
> valid. Add a timeout check and exit if a timeout occurs. As this is
> a very rare condition, handle the timeout only if the first read fails.
>
> Signed-off-by: Ansuel Smith <ansuelsmth@xxxxxxxxx>
> ---
> drivers/thermal/qcom/tsens.c | 23 ++++++++++++++++-------
> 1 file changed, 16 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/thermal/qcom/tsens.c b/drivers/thermal/qcom/tsens.c
> index b1162e566a70..38afde1a599f 100644
> --- a/drivers/thermal/qcom/tsens.c
> +++ b/drivers/thermal/qcom/tsens.c
> @@ -599,6 +599,7 @@ int get_temp_tsens_valid(const struct tsens_sensor *s, int *temp)
> int hw_id = s->hw_id;
> u32 temp_idx = LAST_TEMP_0 + hw_id;
> u32 valid_idx = VALID_0 + hw_id;
> + unsigned long timeout;
> u32 valid;
> int ret;
>
> @@ -607,13 +608,21 @@ int get_temp_tsens_valid(const struct tsens_sensor *s, int *temp)
> ret = regmap_field_read(priv->rf[valid_idx], &valid);
> if (ret)
> return ret;
> - while (!valid) {
> - /* Valid bit is 0 for 6 AHB clock cycles.
> - * At 19.2MHz, 1 AHB clock is ~60ns.
> - * We should enter this loop very, very rarely.
> - */
> - ndelay(400);
> - ret = regmap_field_read(priv->rf[valid_idx], &valid);
> +
> + if (!valid) {
> + timeout = jiffies + msecs_to_jiffies(20);
> +
> + do {
> + /* Valid bit is 0 for 6 AHB clock cycles.
> + * At 19.2MHz, 1 AHB clock is ~60ns.
> + * We should enter this loop very, very rarely.
> + */
> + ndelay(400);
> + ret = regmap_field_read(priv->rf[valid_idx], &valid);
> + if (valid || ret)
> + break;
> + } while (!(ret = time_after_eq(jiffies, timeout)));
> +
> if (ret)
> return ret;
With the overloading of 'ret' the return logic is getting a bit more
convoluted. Also the function should probably return -ETIMEDOUT or
some other meaningful error if the bit is never valid.
How about keeping the 'while (!valid)' condition, and adding
if (time_after_eq(jiffies, timeout))
return -ETIMEDOUT;
inside the loop?
