Re: [PATCH 11/12] hwmon: spd5118: Add I3C support

On Thu, 19 Mar 2026 07:34:18 -0700, Guenter Roeck wrote:
> On 3/18/26 21:35, Akhil R wrote:
>> On Wed, 18 Mar 2026 11:53:49 -0700, Guenter Roeck wrote:
>>> On 3/18/26 10:27, Akhil R wrote:
>>>> Add a regmap config and a probe function to support for I3C based
>>>> communication to SPD5118 devices.
>>>>
>>>> On an I3C bus, SPD5118 are enumerated via SETAASA and always require an
>>>> ACPI or device tree entry. The device matching is hence through the OF
>>>> match tables only and do not need an I3C class match table. The device
>>>> identity is verified in the type registers before proceeding to the
>>>> common probe function.
>>>>
>>>> Signed-off-by: Akhil R <[email protected]>
>>>> ---
>>>>    drivers/hwmon/Kconfig   |  7 +++--
>>>>    drivers/hwmon/spd5118.c | 66 ++++++++++++++++++++++++++++++++++++++++-
>>>>    2 files changed, 70 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
>>>> index 8af80e17d25e..23604c05ad22 100644
>>>> --- a/drivers/hwmon/Kconfig
>>>> +++ b/drivers/hwmon/Kconfig
>>>> @@ -2300,10 +2300,13 @@ config SENSORS_SPD5118
>>>>    	tristate "SPD5118 Compliant Temperature Sensors"
>>>>    	depends on I2C
>>>>    	select REGMAP_I2C
>>>
>>> I also had
>>> 	depends on I3C || I3C=n
>>> in my version at
>>>
>>> https://patchwork.kernel.org/project/linux-hwmon/patch/[email protected]/
>>>
>>> which I guess matches the more recent "depends on I3C_OR_I2C".
>> 
>> Ack. Will update.
>> 
>>>
>>>> +	select REGMAP_I3C if I3C
>>>>    	help
>>>>    	  If you say yes here you get support for SPD5118 (JEDEC JESD300)
>>>> -	  compliant temperature sensors. Such sensors are found on DDR5 memory
>>>> -	  modules.
>>>> +	  compliant temperature sensors using I2C or I3C bus interface.
>>>> +	  Such sensors are found on DDR5 memory modules.
>>>> +
>>>> +	  This driver supports both I2C and I3C interfaces.
>>>>    
>>>>    	  This driver can also be built as a module. If so, the module
>>>>    	  will be called spd5118.
>>>> diff --git a/drivers/hwmon/spd5118.c b/drivers/hwmon/spd5118.c
>>>> index 5da44571b6a0..d70123e10616 100644
>>>> --- a/drivers/hwmon/spd5118.c
>>>> +++ b/drivers/hwmon/spd5118.c
>>>> @@ -18,6 +18,7 @@
>>>>    #include <linux/bits.h>
>>>>    #include <linux/err.h>
>>>>    #include <linux/i2c.h>
>>>> +#include <linux/i3c/device.h>
>>>>    #include <linux/hwmon.h>
>>>>    #include <linux/module.h>
>>>>    #include <linux/mutex.h>
>>>> @@ -482,6 +483,25 @@ static const struct regmap_config spd5118_regmap16_config = {
>>>>    	.cache_type = REGCACHE_MAPLE,
>>>>    };
>>>>    
>>>> +/*
>>>> + * I3C uses 2-byte register addressing -
>>>> + *   Byte 1: MemReg | BlkAddr[0] | Address[5:0]
>>>> + *   Byte 2: 0000   | BlkAddr[4:1]
>>>> + *
>>>> + * The low byte carries the register/NVM address and the high byte carries the
>>>> + * upper block address bits, so little-endian format is required. No range
>>>> + * config is needed since I3C does not use MR11 page switching.
>>>> + */
>>>> +static const struct regmap_config spd5118_regmap_i3c_config = {
>>>> +	.reg_bits = 16,
>>>> +	.val_bits = 8,
>>>> +	.max_register = 0x7ff,
>>>> +	.reg_format_endian = REGMAP_ENDIAN_LITTLE,
>>>
>>> Should this be added to spd5118_regmap16_config instead, or is there reason
>>> to assume that I2C 16-bit addressing differs from I3C addressing ?
>> 
>> I did not see any difference for I2C in the specification, but I assumed the
>> existing format would have been working and I thought not to change them.
>> Changing the I2C format would also require a change in the is_16bit nvmem_read
>> formula.
>> 
>>>
>>>> +	.writeable_reg = spd5118_writeable_reg,
>>>> +	.volatile_reg = spd5118_volatile_reg,
>>>> +	.cache_type = REGCACHE_MAPLE,
>>>> +};
>>>> +
>>>>    static int spd5118_suspend(struct device *dev)
>>>>    {
>>>>    	struct spd5118_data *data = dev_get_drvdata(dev);
>>>> @@ -770,7 +790,51 @@ static struct i2c_driver spd5118_i2c_driver = {
>>>>    	.address_list	= IS_ENABLED(CONFIG_SENSORS_SPD5118_DETECT) ? normal_i2c : NULL,
>>>>    };
>>>>    
>>>> -module_i2c_driver(spd5118_i2c_driver);
>>>> +/* I3C */
>>>> +
>>>> +static int spd5118_i3c_probe(struct i3c_device *i3cdev)
>>>> +{
>>>> +	struct device *dev = i3cdev_to_dev(i3cdev);
>>>> +	struct regmap *regmap;
>>>> +	unsigned int regval;
>>>> +	int err;
>>>> +
>>>> +	regmap = devm_regmap_init_i3c(i3cdev, &spd5118_regmap_i3c_config);
>>>> +	if (IS_ERR(regmap))
>>>> +		return dev_err_probe(dev, PTR_ERR(regmap), "regmap init failed\n");
>>>> +
>>>> +	/* Verify this is a SPD5118 device */
>>>> +	err = regmap_read(regmap, SPD5118_REG_TYPE, &regval);
>>>> +	if (err)
>>>> +		return err;
>>>> +
>>>> +	if (regval != 0x51) {
>>>> +		dev_err(dev, "unexpected device type 0x%02x, expected 0x51\n", regval);
>>>> +		return -ENODEV;
>>>> +	}
>>>> +
>>>> +	err = regmap_read(regmap, SPD5118_REG_TYPE + 1, &regval);
>>>> +	if (err)
>>>> +		return err;
>>>> +
>>>> +	if (regval != 0x18) {
>>>> +		dev_err(dev, "unexpected device type 0x%02x, expected 0x18\n", regval);
>>>> +		return -ENODEV;
>>>> +	}
>>>> +
>>>
>>> I don't think this should dump error messages. Also, it might be desirable
>>> to use a single regmap operation to read both values.
>> 
>> Ack. Will use regmap_bulk_read() and will remove the error dump.
>> 
>>>
>>>> +	return spd5118_common_probe(dev, regmap, false);
>>>
>>> Why is_16bit=false ?
>> 
>> We don't need the encoding formula for the nvmem address with I3C. Since it
>> uses little-endian, (page * 0x100 + SPD5118_EEPROM_BASE) translates to the
>> correct address. Or did I overlook something?
>> 
> 
> Testing of the 16-bit code was limited: I had to set the SPD on a system
> manually to 16-bit mode to get it working, and that only worked until the system
> was reset. Its whole point was to prepare for I3C mode. If that fails, the entire
> 16-bit code in the driver is potentially wrong and should be pulled out before
> adding I3C code. It can be added back later if/when a system actually utilizing
> it is found.

Thanks for letting me know. I will add a patch to remove the I2C 16-bit sections in
the next revision as a prerequistie to this patch. Hope that sounds good.

Best Regards,
Akhil