linux-kernel - Re: [PATCH v4a 6/6] hwmon: (spd5118) Add configuration option for auto-detection

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Message-ID: <b83f47cd-2b4f-4681-8f3e-d6123cbf48ce@roeck-us.net>
Date: Wed, 5 Jun 2024 07:04:51 -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 v4a 6/6] hwmon: (spd5118) Add configuration option for
 auto-detection

On 6/5/24 02:22, Thomas Weißschuh wrote:
> On 2024-06-04 19:19:07+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>
>> ---
>> Sent as v4a to avoid resending the entire series.
>>
>> v4a:
>>      Do not auto-select SENSORS_SPD5118_DETECT if DMI is disabled
>>      Modify help text of SENSORS_SPD5118_DETECT
>>      Default SENSORS_SPD5118_DETECT to y if (!DMI || !X86)
>>       
>> v4: New patch
>>
>>   drivers/hwmon/Kconfig   | 19 +++++++++++++++++++
>>   drivers/hwmon/spd5118.c |  4 +++-
>>   2 files changed, 22 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
>> index 7a84e7637b51..d5eced417fc3 100644
>> --- a/drivers/hwmon/Kconfig
>> +++ b/drivers/hwmon/Kconfig
>> @@ -2193,6 +2193,25 @@ 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 (!DMI || !X86)
>> +	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 X86 systems with DMI support
>> +	  this will typically be done from DMI DDR detection code in the
>> +	  I2C SMBus subsystem. Devicetree based systems will instantiate
>> +	  attached devices if the DIMMs are listed in the devicetree file.
>> +
>> +	  Disabling the detect function will speed up boot time and reduce
>> +	  the risk of mis-detecting SPD5118 compliant devices. However, it
>> +	  may result in missed DIMMs under some circumstances.
>> +
>> +	  If unsure, say Y.
>> +
>>   config SENSORS_TC74
>>   	tristate "Microchip TC74"
>>   	depends on I2C
>> diff --git a/drivers/hwmon/spd5118.c b/drivers/hwmon/spd5118.c
>> index 5cb5e52c0a38..19d203283a21 100644
>> --- a/drivers/hwmon/spd5118.c
>> +++ b/drivers/hwmon/spd5118.c
>> @@ -313,7 +313,7 @@ static bool spd5118_vendor_valid(u8 bank, u8 id)
>>   }
>>   
>>   /* Return 0 if detection is successful, -ENODEV otherwise */
>> -static int spd5118_detect(struct i2c_client *client, struct i2c_board_info *info)
>> +static int __maybe_unused spd5118_detect(struct i2c_client *client, struct i2c_board_info *info)
>>   {
>>   	struct i2c_adapter *adapter = client->adapter;
>>   	int regval;
>> @@ -647,7 +647,9 @@ static struct i2c_driver spd5118_driver = {
>>   	},
>>   	.probe		= spd5118_probe,
>>   	.id_table	= spd5118_id,
>> +#ifdef CONFIG_SENSORS_SPD5118_DETECT
>>   	.detect		= spd5118_detect,
>> +#endif
>>   	.address_list	= normal_i2c,
>>   };
> 
> For the if-deffery I proposed something during the last review,
> I'm not sure if you saw it. If you did, please ignore this comment:
> 

I missed that, sorry (and I hope I didn't miss anything else).

> 
> .address_list is also only needed with CONFIG_SENSORS_SPD5118_DETECT.
> 
> If you use
> 
> .detect         = IS_ENABLED(CONFIG_SENSORS_SPD5118_DETECT) ?  spd5118_detect : NULL,
> .address_list   = IS_ENABLED(CONFIG_SENSORS_SPD5118_DETECT) ?  normal_i2c : NULL,
> 
> then the need for __maybe_unused goes away and type checking is a tiny
> bit better.

It does let me drop the #ifdef, so I agree it is a bit better.
I made that change, but I'll wait for a couple of days before sending
the updated version to give others time for additional feedback.

Thanks,
Guenter