Re: [PATCH v5 16/18] thermal/drivers/tegra: Remove unneeded lock when setting a trip point

[Daniel Lezcano]

On 02/03/2023 10:47, Thierry Reding wrote:
> On Wed, Mar 01, 2023 at 09:14:44PM +0100, Daniel Lezcano wrote:
> > The function tegra_tsensor_enable_hw_channel() takes the thermal zone
> > lock to prevent "a potential" race with a call to set_trips()
> > callback.
> >
> > The driver must not play with the thermal framework core code
> > internals.
> >
> > The tegra_tsensor_enable_hw_channel() is called by:
> >
> >   - the suspend / resume callbacks
> >   - the probe function after the thermal zones are registered
> >
> > The thermal zone lock taken in this function is supposed to protect
> > from a call to the set_trips() callback which writes in the same
> > register.
> >
> > The potential race is when suspend / resume are called at the same
> > time as set_trips. This one is called only in
> > thermal_zone_device_update().
> >
> >   - At suspend time, the 'in_suspend' is set, thus the
> >     thermal_zone_device_update() bails out immediately and set_trips is
> >     not called during this moment.
> >
> >   - At resume time, the thermal zone is updated at PM_POST_SUSPEND,
> >     thus the driver has already set the TH2 temperature.
> >
> >   - At probe time, we register the thermal zone and then we set the
> >     TH2. The only scenario I can see so far is the interrupt fires, the
> >     thermal_zone_update() is called exactly at the moment
> >     tegra_tsensor_enable_hw_channel() a few lines after registering it.
> >
> > Enable the channels before setting up the interrupt. We close the
> > potential race window without using the thermal zone's lock.
> >
> > Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
> > Suggested-by: Thierry Reding <thierry.reding@xxxxxxxxx>
> > ---
> >   drivers/thermal/tegra/tegra30-tsensor.c | 25 ++++++++++++++-----------
> >   1 file changed, 14 insertions(+), 11 deletions(-)
>
> Acked-by: Thierry Reding <treding@xxxxxxxxxx>

Thanks for your review

May I ask you to have a look at patch 2 and 8 ?

Thanks

  -- Daniel

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