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

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Date: Tue, 4 Jun 2024 07:04:09 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Thomas Weißschuh <linux@...ssschuh.net>
Cc: linux-hwmon@...r.kernel.org, linux-i2c@...r.kernel.org,
 linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
 Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Wolfram Sang <wsa+renesas@...g-engineering.com>,
 René Rebe <rene@...ctcode.de>, Armin Wolf <W_Armin@....de>,
 Stephen Horvath <s.horvath@...look.com.au>
Subject: Re: [PATCH v4 6/6] hwmon: (spd5118) Add configuration option for
 auto-detection

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@...g-engineering.com>
>> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
>> ---
>> 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