Hello Andrew,
Thanks for your feedback, I really appreciate your effort reviewing this
work.
On 2024-05-08 16:00:21 +0200, Andrew Lunn wrote:
> > I agree it's odd and I will try to find out.
> >
> > If I remove all pm_ calls and the include of pm_runtime.h register reads
> > from the device do no longer works, so operating the device fails. Even
> > if I dig out the root cause for this, is there any harm in keeping the
> > pm_ operations in the initial entablement?
>
> It suggests something is broken. Do we want to merge broken code?
Of course I do not want broken code merged. I was curious if you knew of
any harmful side effect of of using pm_ functions I was unaware of.
>
> Once we understand the root cause maybe then we can decide it is O.K.
The root cause is that the module clock is not enabled without some
action. If I remove all pm_ calls as well as the inclusion of
linux/pm_runtime.h. The tsn module clock is left disabled after probe
completes.
# grep . /sys/kernel/debug/clk/tsn/*
/sys/kernel/debug/clk/tsn/clk_accuracy:0
/sys/kernel/debug/clk/tsn/clk_duty_cycle:1/2
/sys/kernel/debug/clk/tsn/clk_enable_count:0
/sys/kernel/debug/clk/tsn/clk_flags:CLK_SET_RATE_PARENT
/sys/kernel/debug/clk/tsn/clk_max_rate:18446744073709551615
/sys/kernel/debug/clk/tsn/clk_min_rate:0
/sys/kernel/debug/clk/tsn/clk_notifier_count:0
/sys/kernel/debug/clk/tsn/clk_parent:s0d4_hsc
/sys/kernel/debug/clk/tsn/clk_phase:0
/sys/kernel/debug/clk/tsn/clk_prepare_count:1
/sys/kernel/debug/clk/tsn/clk_protect_count:0
/sys/kernel/debug/clk/tsn/clk_rate:199999992
As the clock is disabled trying to operate the device is not possible.
The clock can either be enabled by the pm_ calls as show or be replaced
by an explicit clk_enable(), like this (the other pm_ related
calls/includes are of course also removed).
- pm_runtime_enable(&pdev->dev);
- pm_runtime_get_sync(&pdev->dev);
+ clk_enable(priv->clk);
Either of the two methods leaves the module clock running and the driver
can operate the device.
# grep . /sys/kernel/debug/clk/tsn/*
/sys/kernel/debug/clk/tsn/clk_accuracy:0
/sys/kernel/debug/clk/tsn/clk_duty_cycle:1/2
/sys/kernel/debug/clk/tsn/clk_enable_count:1
/sys/kernel/debug/clk/tsn/clk_flags:CLK_SET_RATE_PARENT
/sys/kernel/debug/clk/tsn/clk_max_rate:18446744073709551615
/sys/kernel/debug/clk/tsn/clk_min_rate:0
/sys/kernel/debug/clk/tsn/clk_notifier_count:0
/sys/kernel/debug/clk/tsn/clk_parent:s0d4_hsc
/sys/kernel/debug/clk/tsn/clk_phase:0
/sys/kernel/debug/clk/tsn/clk_prepare_count:1
/sys/kernel/debug/clk/tsn/clk_protect_count:0
/sys/kernel/debug/clk/tsn/clk_rate:199999992
I would prefer to keep the pm_ operations, but if you prefer I can
switch to using clk_enable().
--
Kind Regards,
Niklas Söderlund
