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SubjectRe: [PATCH] hwmon:max6697: Allow max6581 to set temperature read offset
On Tue, Jun 30, 2020 at 05:43:50PM +0000, Chu Lin wrote:
> Per max6581, reg 4d and reg 4e is used for temperature read offset.
> This patch will let the user specify the temperature read offset for
> max6581. This patch is tested on max6581 and only applies to max6581.
>
> Testing:
> dts: temperature-read-offset = <0xde 0x0>;

This should not be implemented this way. Instead, the standard tempX_offset
attribute should be used, with appropriate code to determine affected
channels (since there is only one offset value, and since it can be enabled
per channel). A secondary question is if and how to set the temperature
offset via devicetree; that will have to be documented and approved by a
DT maintainer. I would think, though, that the offset should be specified
in milli-degrees C and not as raw chip data.

Thanks,
Guenter

>
> verify: iotools smbus_read8 <vbus> 0x4d 0x4e
> 0x6F
>
> Signed-off-by: Chu Lin <linchuyuan@google.com>
> ---
> drivers/hwmon/max6697.c | 19 +++++++++++++++++--
> include/linux/platform_data/max6697.h | 4 ++++
> 2 files changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/hwmon/max6697.c b/drivers/hwmon/max6697.c
> index 743752a2467a..16c0f0995a12 100644
> --- a/drivers/hwmon/max6697.c
> +++ b/drivers/hwmon/max6697.c
> @@ -493,8 +493,13 @@ static void max6697_get_config_of(struct device_node *node,
> }
> prop = of_get_property(node, "transistor-ideality", &len);
> if (prop && len == 2 * sizeof(u32)) {
> - pdata->ideality_mask = be32_to_cpu(prop[0]);
> - pdata->ideality_value = be32_to_cpu(prop[1]);
> + pdata->ideality_mask = be32_to_cpu(prop[0]);
> + pdata->ideality_value = be32_to_cpu(prop[1]);
> + }
> + prop = of_get_property(node, "temperature-read-offset", &len);
> + if (prop && len == 2 * sizeof(u32)) {
> + pdata->offset_mask = be32_to_cpu(prop[0]);
> + pdata->offset_value = be32_to_cpu(prop[1]);
> }
> }
>
> @@ -586,6 +591,16 @@ static int max6697_init_chip(struct max6697_data *data,
> pdata->ideality_mask >> 1);
> if (ret < 0)
> return ret;
> + ret = i2c_smbus_write_byte_data(client,
> + MAX6581_REG_OFFSET,
> + pdata->offset_value);
> + if (ret < 0)
> + return ret;
> + ret = i2c_smbus_write_byte_data(client,
> + MAX6581_REG_OFFSET_SELECT,
> + pdata->offset_mask >> 1);
> + if (ret < 0)
> + return ret;
> }
> done:
> data->update_interval = factor * MAX6697_CONV_TIME;
> diff --git a/include/linux/platform_data/max6697.h b/include/linux/platform_data/max6697.h
> index 6fbb70005541..ff98adfe9d8d 100644
> --- a/include/linux/platform_data/max6697.h
> +++ b/include/linux/platform_data/max6697.h
> @@ -28,6 +28,10 @@ struct max6697_platform_data {
> u8 ideality_value; /* transistor ideality as per
> * MAX6581 datasheet
> */
> + u8 offset_mask; /* set bit to 0 to disable */
> + u8 offset_value; /* temperature read offset as
> + * MAX6581 datasheet
> + */
> };
>
> #endif /* MAX6697_H */
> --
> 2.27.0.212.ge8ba1cc988-goog
>

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