Re: [PATCH v4 6/6] hwmon: (spd5118) Add configuration option for auto-detection

[Guenter Roeck]

On 6/3/24 21:37, Thomas Weißschuh wrote:
> On 2024-06-03 21:02:37+0000, Guenter Roeck wrote:
> > With SPD5118 chip detection for the most part handled by the i2c-smbus
> > core using DMI information, the spd5118 driver no longer needs to
> > auto-detect spd5118 compliant chips.
> >
> > Auto-detection by the driver is still needed on systems with no DMI support
> > or on systems with more than eight DIMMs and can not be removed entirely.
> > However, it affects boot time and introduces the risk of mis-identifying
> > chips. Add configuration option to be able to disable it on systems where
> > chip detection is handled outside the driver.
> >
> > Cc: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > ---
> > v4: New patch
> >
> >   drivers/hwmon/Kconfig   | 18 ++++++++++++++++++
> >   drivers/hwmon/spd5118.c |  4 +++-
> >   2 files changed, 21 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
> > index 7a84e7637b51..0bb1bdee3e43 100644
> > --- a/drivers/hwmon/Kconfig
> > +++ b/drivers/hwmon/Kconfig
> > @@ -2185,6 +2185,7 @@ config SENSORS_SPD5118
> >   	tristate "SPD5118 Compliant Temperature Sensors"
> >   	depends on I2C
> >   	select REGMAP_I2C
> > +	select SENSORS_SPD5118_DETECT if !DMI
> >   	help
> >   	  If you say yes here you get support for SPD5118 (JEDEC JESD300)
> >   	  compliant temperature sensors. Such sensors are found on DDR5 memory
> > @@ -2193,6 +2194,23 @@ config SENSORS_SPD5118
> >   	  This driver can also be built as a module. If so, the module
> >   	  will be called spd5118.
> >   
> > +config SENSORS_SPD5118_DETECT
> > +	bool "Enable detect function"
> > +	depends on SENSORS_SPD5118
> > +	default y
> > +	help
> > +	  If enabled, the driver auto-detects if a chip in the SPD address
> > +	  range is compliant to the SPD51888 standard and auto-instantiates
> > +	  if that is the case. If disabled, SPD5118 compliant devices have
> > +	  to be instantiated by other means. On systems with DMI support
> > +	  this will typically be done from DMI DDR detection code in the
> > +	  I2C SMBus subsystem.
> > +	  Disabling the detect function will speed up boot time and reduce
> > +	  the risk of mis-detecting SPD5118 compliant devices. In general
> > +	  it should only be enabled if necessary.
> > +
> > +	  If unsure, say Y.
>
> The combination of
>
> "In general it should only be enabled if necessary."
>
> and
>
> "default y" / "If unsure, say Y."
>
> looks weird.

Yes, I know. I just couldn't find a better wording.

> Also right now it is not possible to disable detection on non-DMI
> configurations. But when using OF, custom kernel code or userspace
> instantiation then neither DMI nor CONFIG_DETECT are necessary.

That is a good point.

> The following would support those usecases, too:
>
> config SENSORS_SPD5118_DETECT
> 	bool "Enable detect function"
> 	depends on SENSORS_SPD5118
> 	default !DMI
>
> (And no "select SENSORS_SPD5118_DETECT if !DMI")

I don't think "default !DMI" would be a good idea because DMI
is supported by multiple architectures, but only two X86 specific
controllers call i2c_register_spd().

"default !DMI || !X86" might work, though. I think I'll use that.

I'll rephrase the text and drop the "select".

Thanks,
Guenter