On 26/10/2022 15:23, Uwe Kleine-König wrote:
On Wed, Oct 26, 2022 at 11:13:05AM +0100, Jon Hunter wrote:
If the 'required_clk_rate' is greater than the clock rate that can be
provided, then when mul_u64_u64_div_u64() is called to determine the
'rate' for the PWM divider, 0 will be returned. If 'rate' is 0, then we
will return -EINVAL and fail to configure the PWM. Fix this by adding 1
to the PWM_DUTY_WIDTH when calculating the 'required_clk_rate' to ensure
that 'rate' is greater or equal to 1. This fixes an issue on Tegra234
where configuring the PWM fan fails.
Fixes: 8c193f4714df ("pwm: tegra: Optimize period calculation")
Signed-off-by: Jon Hunter <jonathanh@xxxxxxxxxx>
---
drivers/pwm/pwm-tegra.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/drivers/pwm/pwm-tegra.c b/drivers/pwm/pwm-tegra.c
index 8a33c500f93b..973e2c1533ab 100644
--- a/drivers/pwm/pwm-tegra.c
+++ b/drivers/pwm/pwm-tegra.c
@@ -148,6 +148,19 @@ static int tegra_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
required_clk_rate = DIV_ROUND_UP_ULL((NSEC_PER_SEC << PWM_DUTY_WIDTH),
period_ns);
+ /*
+ * If the 'required_clk_rate' is greater than the clock rate
+ * that can be provided, then when mul_u64_u64_div_u64() is
+ * called to determine the 'rate' for the PWM divider, 0 will
+ * be returned. If 'rate' is 0, then we will return -EINVAL and
+ * fail to configure the PWM. If this case, add 1 to the
+ * PWM_DUTY_WIDTH when calculating the 'required_clk_rate' to
+ * ensure that 'rate' is greater or equal to 1.
+ */
+ if (required_clk_rate > clk_round_rate(pc->clk, required_clk_rate))
+ required_clk_rate = DIV_ROUND_UP_ULL((NSEC_PER_SEC << (PWM_DUTY_WIDTH + 1)),
+ period_ns);
+
It's implicit knowledge that (roughly) doubling the clk rate is the
right value (i.e the minimal value to get a
clk_rate >= (NSEC_PER_SEC << PWM_DUTY_WIDTH) / period_ns?
Are you suggesting I drop the comment? Sorry not sure what you are
trying to say here and if you think something should be changed.
err = dev_pm_opp_set_rate(pc->dev, required_clk_rate);
if (err < 0)
return -EINVAL;
Is it obvious that dev_pm_opp_set_rate(pc->dev, ...) and
clk_round_rate() correlate enough that the latter tells anything about
the former? Would it make sense to use clk_set_rate instead of
dev_pm_opp_set_rate?
We call clk_get_rate() after calling dev_pm_opp_set_rate() and so
hopefully when reviewing the complete code it is clearer. I don't think
we can use clk_set_rate() and this was changed from calling
clk_set_rate() by commit 3da9b0feaa16 ("pwm: tegra: Add runtime PM and
OPP support").
Thanks
Jon
--
nvpublic
