Re: [PATCH 2/3] thermal: qoriq_thermal: only enable supported sensors

[Daniel Lezcano]

On 07/06/2023 08:01, Sebastian Krzyszkowiak wrote:
> On piątek, 2 czerwca 2023 15:11:37 CEST Daniel Lezcano wrote:
> > On 01/06/2023 11:52, Peng Fan wrote:
> > > Hi Daniel,
> > >
> > > > Subject: RE: [PATCH 2/3] thermal: qoriq_thermal: only enable supported
> > > > sensors
> > > >
> > > > > Subject: Re: [PATCH 2/3] thermal: qoriq_thermal: only enable supported
> > > > > sensors
> > > > >
> > > > > On 31/05/2023 14:05, Peng Fan wrote:
> > > > > > > Subject: Re: [PATCH 2/3] thermal: qoriq_thermal: only enable
> > > > > > > supported sensors
> > > > > > >
> > > > > > > On 16/05/2023 10:37, Peng Fan (OSS) wrote:
> > > > > > > > From: Peng Fan <peng.fan@xxxxxxx>
> > > > > > > >
> > > > > > > > There are MAX 16 sensors, but not all of them supported. Such as
> > > > > > > > i.MX8MQ, there are only 3 sensors. Enabling all 16 sensors will
> > > > > > > > touch reserved bits from i.MX8MQ reference mannual, and TMU will
> > > > > > > > stuck, temperature will not update anymore.
> > > > > > > >
> > > > > > > > Fixes: 45038e03d633 ("thermal: qoriq: Enable all sensors before
> > > > > > > > registering them")
> > > > > > > > Signed-off-by: Peng Fan <peng.fan@xxxxxxx>
> > > > > > > > ---
> > > > > > > >
> > > > > > > >      drivers/thermal/qoriq_thermal.c | 30
> > > > > > > >      +++++++++++++++++++----------
> > > >
> > > > -
> > > >
> > > > > > > >      1 file changed, 19 insertions(+), 11 deletions(-)
> > > > > > > >
> > > > > > > > diff --git a/drivers/thermal/qoriq_thermal.c
> > > > > > > > b/drivers/thermal/qoriq_thermal.c index
> > > >
> > > > b806a0929459..53748c4a5be1
> > > >
> > > > > > > > 100644
> > > > > > > > --- a/drivers/thermal/qoriq_thermal.c
> > > > > > > > +++ b/drivers/thermal/qoriq_thermal.c
> > > > > > > > @@ -31,7 +31,6 @@
> > > > > > > >
> > > > > > > >      #define TMR_DISABLE	0x0
> > > > > > > >      #define TMR_ME		0x80000000
> > > > > > > >      #define TMR_ALPF	0x0c000000
> > > > > > > >
> > > > > > > > -#define TMR_MSITE_ALL	GENMASK(15, 0)
> > > > > > > >
> > > > > > > >      #define REGS_TMTMIR	0x008	/* Temperature measurement
> > > > > > >
> > > > > > > interval Register */
> > > > > > >
> > > > > > > >      #define TMTMIR_DEFAULT	0x0000000f
> > > > > > > >
> > > > > > > > @@ -105,6 +104,11 @@ static int tmu_get_temp(struct
> > > > > > >
> > > > > > > thermal_zone_device *tz, int *temp)
> > > > > > >
> > > > > > > >      	 * within sensor range. TEMP is an 9 bit value representing
> > > > > > > >      	 * temperature in KelVin.
> > > > > > > >      	 */
> > > > > > > >
> > > > > > > > +
> > > > > > > > +	regmap_read(qdata->regmap, REGS_TMR, &val);
> > > > > > > > +	if (!(val & TMR_ME))
> > > > > > > > +		return -EAGAIN;
> > > > > > >
> > > > > > > How is this change related to what is described in the changelog?
> > > > > >
> > > > > > devm_thermal_zone_of_sensor_register will invoke get temp, since we
> > > > > > reverted the 45038e03d633 did, we need to check TMR_ME to avoid
> > > > >
> > > > > return
> > > > >
> > > > > > invalid temperature.
> > > > >    From a higher perspective if the sensor won't be enabled, then the
> > > > >
> > > > > thermal zone should not be registered, the get_temp won't happen on a
> > > > > disabled sensor and this test won't be necessary, no ?
> > >
> > > After thinking more, I'd prefer current logic.
> > >
> > > We rely on devm_thermal_of_zone_register's return value to know
> > > whether there is a valid zone, then set sites bit, and after collected
> > > all site bits, we enable the thermal IP.
> > >
> > > If move the enabling thermal IP before devm_thermal_of_zone_register,
> > > We need check dtb thermal zone, to know which zone is valid for current
> > > thermal IP. This would complicate the design.
> > >
> > > So just checking the enabling bit in get temperature would be much
> > > simpler, and there just a small window before enabling thermal IP.
> >
> > If the thermal zone is not described, then the thermal zone won't be
> > created as it fails with -ENODEV and thus get_temp won't be called on a
> > disabled site, right?
>
> That's not what the problem is. It's about zones that *will* be created -
> since the driver only knows that a thermal zone isn't described in the device
> tree after it fails registering, it can't enable the site *before* the zone
> gets registered - so it happens afterwards. That's why it needs this check to
> not return a bogus initial value before the site gets actually enabled later
> in qoriq_tmu_register_tmu_zone.

Sorry, I get the point but I don't see how that can happen:

qoriq_tmu_register_tmu_zone() calls devm_thermal_of_zone_register() for 
*all* sites regardless if they really exists or not.

Under the hood, the function devm_thermal_of_zone_register() calls 
thermal_of_zone_register(). This one fails when calling 
of_thermal_zone_find() because it does not exist and returns -ENODEV.

Hence, the thermal_zone_device_register_with_trips() is not called, the 
thermal zone is not created neither updated.

So I don't understand why the test:

+	regmap_read(qdata->regmap, REGS_TMR, &val);
+	if (!(val & TMR_ME))
+		return -EAGAIN;

is needed in the get_temp() ops as the thermal zone for this disabled 
site should not exist.

I'm not putting in question the series, just wanting to avoid a 
potential pointless check in an ops.


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