[v2] thermal: core: Allow thermal zones to tell the core to ignore them

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

The iwlwifi wireless driver registers a thermal zone that is only needed
when the network interface handled by it is up and it wants that thermal
zone to be effectively ignored by the core otherwise.

Before commit a8a261774466 ("thermal: core: Call monitor_thermal_zone()
if zone temperature is invalid") that could be achieved by returning
an error code from the thermal zone's .get_temp() callback because the
core did not really handle errors returned by it almost at all.
However, commit a8a261774466 made the core attempt to recover from the
situation in which the temperature of a thermal zone cannot be
determined due to errors returned by its .get_temp() and is always
invalid from the core's perspective.

That was done because there are thermal zones in which .get_temp()
returns errors to start with due to some difficulties related to the
initialization ordering, but then it will start to produce valid
temperature values at one point.

Unfortunately, the simple approach taken by commit a8a261774466,
which is to poll the thermal zone periodically until its .get_temp()
callback starts to return valid temperature values, is at odds with
the special thermal zone in iwlwifi in which .get_temp() may always
return an error because its network interface may always be down.  If
that happens, every attempt to invoke the thermal zone's .get_temp()
callback resulting in an error causes the thermal core to print a
dev_warn() message to the kernel log which is super-noisy.

To address this problem, make the core handle the case in which
.get_temp() returns 0, but the temperature value returned by it
is not actually valid, in a special way.  Namely, make the core
completely ignore the invalid temperature value coming from
.get_temp() in that case, which requires folding in
update_temperature() into its caller and a few related changes.

On the iwlwifi side, modify iwl_mvm_tzone_get_temp() to return 0
and put THERMAL_TEMP_INVALID into the temperature return memory
location instead of returning an error when the firmware is not
running or it is not of the right type.

Also, to clearly separate the handling of invalid temperature
values from the thermal zone initialization, introduce a special
THERMAL_TEMP_INIT value specifically for the latter purpose.

Fixes: a8a261774466 ("thermal: core: Call monitor_thermal_zone() if zone temperature is invalid")
Closes: https://lore.kernel.org/linux-pm/20240715044527.GA1544@sol.localdomain/
Reported-by: Eric Biggers <ebiggers@kernel.org>
Reported-by: Stefan Lippers-Hollmann <s.l-h@gmx.de>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=201761
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Tested-by: Stefan Lippers-Hollmann <s.l-h@gmx.de>
Cc: 6.10+ <stable@vger.kernel.org> # 6.10+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---

v1 -> v2:
   * It is safer to retain the old behavior in thermal_zone_get_temp(),
     which is the second place where the .get_temp() zone callback is
     used, so make it return -ENODATA if the temperature value coming
     from that callback is invalid.
   * Add Tested-by: for Stefan.

I have retained the previous Tested-by because the part of the patch that has
been tested remains unchanged.

---
 drivers/net/wireless/intel/iwlwifi/mvm/tt.c |    7 +++
 drivers/thermal/thermal_core.c              |   51 +++++++++++++---------------
 drivers/thermal/thermal_core.h              |    3 +
 drivers/thermal/thermal_helpers.c           |    2 +
 4 files changed, 35 insertions(+), 28 deletions(-)

On Wed, Jul 17, 2024 at 09:45:02PM +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> The iwlwifi wireless driver registers a thermal zone that is only needed
> when the network interface handled by it is up and it wants that thermal
> zone to be effectively ignored by the core otherwise.
> 
> Before commit a8a261774466 ("thermal: core: Call monitor_thermal_zone()
> if zone temperature is invalid") that could be achieved by returning
> an error code from the thermal zone's .get_temp() callback because the
> core did not really handle errors returned by it almost at all.
> However, commit a8a261774466 made the core attempt to recover from the
> situation in which the temperature of a thermal zone cannot be
> determined due to errors returned by its .get_temp() and is always
> invalid from the core's perspective.
> 
> That was done because there are thermal zones in which .get_temp()
> returns errors to start with due to some difficulties related to the
> initialization ordering, but then it will start to produce valid
> temperature values at one point.
> 
> Unfortunately, the simple approach taken by commit a8a261774466,
> which is to poll the thermal zone periodically until its .get_temp()
> callback starts to return valid temperature values, is at odds with
> the special thermal zone in iwlwifi in which .get_temp() may always
> return an error because its network interface may always be down.  If
> that happens, every attempt to invoke the thermal zone's .get_temp()
> callback resulting in an error causes the thermal core to print a
> dev_warn() message to the kernel log which is super-noisy.
> 
> To address this problem, make the core handle the case in which
> .get_temp() returns 0, but the temperature value returned by it
> is not actually valid, in a special way.  Namely, make the core
> completely ignore the invalid temperature value coming from
> .get_temp() in that case, which requires folding in
> update_temperature() into its caller and a few related changes.
> 
> On the iwlwifi side, modify iwl_mvm_tzone_get_temp() to return 0
> and put THERMAL_TEMP_INVALID into the temperature return memory
> location instead of returning an error when the firmware is not
> running or it is not of the right type.
> 
> Also, to clearly separate the handling of invalid temperature
> values from the thermal zone initialization, introduce a special
> THERMAL_TEMP_INIT value specifically for the latter purpose.
> 
> Fixes: a8a261774466 ("thermal: core: Call monitor_thermal_zone() if zone temperature is invalid")
> Closes: https://lore.kernel.org/linux-pm/20240715044527.GA1544@sol.localdomain/
> Reported-by: Eric Biggers <ebiggers@kernel.org>
> Reported-by: Stefan Lippers-Hollmann <s.l-h@gmx.de>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=201761
> Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
> Tested-by: Stefan Lippers-Hollmann <s.l-h@gmx.de>
> Cc: 6.10+ <stable@vger.kernel.org> # 6.10+
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
> 
> v1 -> v2:
>    * It is safer to retain the old behavior in thermal_zone_get_temp(),
>      which is the second place where the .get_temp() zone callback is
>      used, so make it return -ENODATA if the temperature value coming
>      from that callback is invalid.
>    * Add Tested-by: for Stefan.
> 
> I have retained the previous Tested-by because the part of the patch that has
> been tested remains unchanged.
> 
> ---
>  drivers/net/wireless/intel/iwlwifi/mvm/tt.c |    7 +++
>  drivers/thermal/thermal_core.c              |   51 +++++++++++++---------------
>  drivers/thermal/thermal_core.h              |    3 +
>  drivers/thermal/thermal_helpers.c           |    2 +
>  4 files changed, 35 insertions(+), 28 deletions(-)

This makes the log messages go away for me.  However I had to resolve a conflict
in drivers/net/wireless/intel/iwlwifi/mvm/tt.c to apply this patch to the latest
upstream.

- Eric