Quoting victor.duicu@xxxxxxxxxxxxx (2024-10-18 14:06:24)
> From: Victor Duicu <victor.duicu@xxxxxxxxxxxxx>
>
> This driver implements ACPI support to Microchip pac1921.
> The driver can read shunt resistor value and label from ACPI table.
>
> Signed-off-by: Victor Duicu <victor.duicu@xxxxxxxxxxxxx>
> ---
>
> The patch was tested on minnowboard and sama5.
>
> Differences related to previous versions:
> v5:
I think v4 was cleaner. Are the following changes necessary?
> - set maximum acceptable value of shunt resistor to 2KOHM in devicetree,
> ACPI table and user input. The chosen value is lesser than INT_MAX,
> which is about 2.1KOHM.
I would personally keep INT_MAX since the limitation is only given by the types
used in the current conversions (see pac1921_calc_scale()) rather than being a
specific PAC1921 hardware limitation. Otherwise I would extend the comment on
top of those two definitions explaining why that's the maximum.
> - in pac1921_match_acpi_device and pac1921_parse_of_fw change to only
> read 32b values for resistor shunt.
>
I think that in pac1921_match_acpi_device(), the u64 temp var was introduced to
address the possible overflow coming from the u64 rez->package.elements[0].integer.value
and to safely perform a sanity check. I don't think we can trust blindly that
the ACPI table always has a valid 32bit value in that field.
pac1921_parse_of_fw() doesn't look changed compared to v4, you already switched
back to device_property_read_u32, if it's what you are referring to.
>
> v4:
> - change name of pac1921_shunt_is_valid to pac1921_shunt_is_invalid.
> - fix coding style.
> - in pac1921_parse_of_fw change back to device_property_read_u32.
>
> v3:
> - simplify and make inline function pac1921_shunt_is_valid. Make argument u64.
> - fix link to DSM documentation.
> - in pac1921_match_acpi_device and pac1921_parse_of_fw, the shunt value is
> read as u64.
> - in pac1921_parse_of_fw remove code for reading label value from
> devicetree.
> - in pac1921_write_shunt_resistor cast the multiply result to u64 in order
> to fix overflow.
>
> v2:
> - remove name variable from priv. Driver reads label attribute with
> sysfs.
> - define pac1921_shunt_is_valid function.
> - move default assignments in pac1921_probe to original position.
> - roll back coding style changes.
> - add documentation for DSM(the linked document was used as reference).
> - remove acpi_match_device in pac1921_match_acpi_device.
> - remove unnecessary null assignment and comment.
> - change name of function pac1921_match_of_device to
> pac1921_parse_of_fw.
>
> v1:
> - initial version for review.
>
> drivers/iio/adc/pac1921.c | 109 +++++++++++++++++++++++++++++++++-----
> 1 file changed, 96 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/iio/adc/pac1921.c b/drivers/iio/adc/pac1921.c
> index a96fae546bc1..9622b0da6196 100644
> --- a/drivers/iio/adc/pac1921.c
> +++ b/drivers/iio/adc/pac1921.c
> @@ -67,6 +67,13 @@ enum pac1921_mxsl {
> #define PAC1921_DEFAULT_DI_GAIN 0 /* 2^(value): 1x gain (HW default) */
> #define PAC1921_DEFAULT_NUM_SAMPLES 0 /* 2^(value): 1 sample (HW default) */
>
> +#define PAC1921_ACPI_GET_UOHMS_VALS 0
> +#define PAC1921_ACPI_GET_LABEL 1
> +#define PAC1921_DSM_UUID "f7bb9932-86ee-4516-a236-7a7a742e55cb"
> +/*The maximum accepted value of shunt_resistor is 2Kohms */
> +#define PAC1921_MAX_SHUNT_VALUE_OHMS 2000
> +#define PAC1921_MAX_SHUNT_VALUE_UOHMS 2000000000
> +
> /*
> * Pre-computed scale factors for BUS voltage
> * format: IIO_VAL_INT_PLUS_NANO
> @@ -204,6 +211,11 @@ struct pac1921_priv {
> } scan;
> };
>
> +static inline bool pac1921_shunt_is_invalid(u32 shunt_val)
> +{
> + return (shunt_val == 0 || shunt_val > PAC1921_MAX_SHUNT_VALUE_UOHMS);
> +}
> +
> /*
> * Check if first integration after configuration update has completed.
> *
> @@ -781,7 +793,7 @@ static ssize_t pac1921_write_shunt_resistor(struct iio_dev *indio_dev,
> const char *buf, size_t len)
> {
> struct pac1921_priv *priv = iio_priv(indio_dev);
> - u64 rshunt_uohm;
> + u32 rshunt_uohm;
> int val, val_fract;
> int ret;
>
> @@ -791,9 +803,13 @@ static ssize_t pac1921_write_shunt_resistor(struct iio_dev *indio_dev,
> ret = iio_str_to_fixpoint(buf, 100000, &val, &val_fract);
> if (ret)
> return ret;
> +
> + /* This check is to ensure val*MICRO won't overflow*/
> + if (val < 0 || val > PAC1921_MAX_SHUNT_VALUE_OHMS)
> + return -EINVAL;
>
> rshunt_uohm = val * MICRO + val_fract;
> - if (rshunt_uohm == 0 || rshunt_uohm > INT_MAX)
> + if (pac1921_shunt_is_invalid(rshunt_uohm))
> return -EINVAL;
>
In v3 you added the (u64)val cast to solve the multiplication overflow. Wasn't
that enough? However, if this is for better clarity I am fine with it.
> guard(mutex)(&priv->lock);
> @@ -1150,6 +1166,71 @@ static void pac1921_regulator_disable(void *data)
> regulator_disable(regulator);
> }
>
> +/*
> + * documentation related to the ACPI device definition
> + * https://ww1.microchip.com/downloads/aemDocuments/documents/OTH/ApplicationNotes/ApplicationNotes/PAC193X-Integration-Notes-for-Microsoft-Windows-10-and-Windows-11-Driver-Support-DS00002534.pdf
> + */
> +static int pac1921_match_acpi_device(struct i2c_client *client, struct pac1921_priv *priv,
> + struct iio_dev *indio_dev)
> +{
> + acpi_handle handle;
> + union acpi_object *rez;
> + guid_t guid;
> + char *label;
> + u32 temp;
> +
> + guid_parse(PAC1921_DSM_UUID, &guid);
> + handle = ACPI_HANDLE(&client->dev);
> +
> + rez = acpi_evaluate_dsm(handle, &guid, 1, PAC1921_ACPI_GET_UOHMS_VALS, NULL);
> + if (!rez)
> + return dev_err_probe(&client->dev, -EINVAL,
> + "Could not read shunt from ACPI table\n");
> +
> + temp = rez->package.elements[0].integer.value;
I don't think we can trust rez->package.elements[0].integer.value to always be
in 32bit boundaries. But if that's the case then the temp var looks unnecessary.
> + ACPI_FREE(rez);
> +
> + if (pac1921_shunt_is_invalid(temp))
> + return dev_err_probe(&client->dev, -EINVAL, "Invalid shunt resistor\n");
> +
> + priv->rshunt_uohm = temp;
> + pac1921_calc_current_scales(priv);
> +
> + rez = acpi_evaluate_dsm(handle, &guid, 1, PAC1921_ACPI_GET_LABEL, NULL);
> + if (!rez)
> + return dev_err_probe(&client->dev, -EINVAL,
> + "Could not read label from ACPI table\n");
> +
> + label = devm_kmemdup(&client->dev, rez->package.elements->string.pointer,
> + (size_t)rez->package.elements->string.length + 1,
> + GFP_KERNEL);
> + label[rez->package.elements->string.length] = '\0';
> + indio_dev->label = label;
> + ACPI_FREE(rez);
> +
> + return 0;
> +}
> +
> +static int pac1921_parse_of_fw(struct i2c_client *client, struct pac1921_priv *priv)
> +{
> + int ret;
> + struct device *dev = &client->dev;
> +
> + ret = device_property_read_u32(dev, "shunt-resistor-micro-ohms",
> + &priv->rshunt_uohm);
> + if (ret)
> + return dev_err_probe(dev, ret,
> + "Cannot read shunt resistor property\n");
> +
> + if (pac1921_shunt_is_invalid(priv->rshunt_uohm))
> + return dev_err_probe(dev, -EINVAL, "Invalid shunt resistor: %u\n",
> + priv->rshunt_uohm);
> +
> + pac1921_calc_current_scales(priv);
> +
> + return 0;
> +}
> +
> static int pac1921_probe(struct i2c_client *client)
> {
> struct device *dev = &client->dev;
> @@ -1176,17 +1257,13 @@ static int pac1921_probe(struct i2c_client *client)
> priv->di_gain = PAC1921_DEFAULT_DI_GAIN;
> priv->n_samples = PAC1921_DEFAULT_NUM_SAMPLES;
>
> - ret = device_property_read_u32(dev, "shunt-resistor-micro-ohms",
> - &priv->rshunt_uohm);
> - if (ret)
> - return dev_err_probe(dev, ret,
> - "Cannot read shunt resistor property\n");
> - if (priv->rshunt_uohm == 0 || priv->rshunt_uohm > INT_MAX)
> - return dev_err_probe(dev, -EINVAL,
> - "Invalid shunt resistor: %u\n",
> - priv->rshunt_uohm);
> -
> - pac1921_calc_current_scales(priv);
> + if (ACPI_HANDLE(&client->dev))
> + ret = pac1921_match_acpi_device(client, priv, indio_dev);
> + else
> + ret = pac1921_parse_of_fw(client, priv);
> + if (ret < 0)
> + return dev_err_probe(&client->dev, ret,
> + "parameter parsing error\n");
>
> priv->vdd = devm_regulator_get(dev, "vdd");
> if (IS_ERR(priv->vdd))
> @@ -1243,11 +1320,17 @@ static const struct of_device_id pac1921_of_match[] = {
> };
> MODULE_DEVICE_TABLE(of, pac1921_of_match);
>
> +static const struct acpi_device_id pac1921_acpi_match[] = {
> + { "MCHP1921" },
> + { }
> +};
> +MODULE_DEVICE_TABLE(acpi, pac1921_acpi_match);
> static struct i2c_driver pac1921_driver = {
> .driver = {
> .name = "pac1921",
> .pm = pm_sleep_ptr(&pac1921_pm_ops),
> .of_match_table = pac1921_of_match,
> + .acpi_match_table = pac1921_acpi_match
> },
> .probe = pac1921_probe,
> .id_table = pac1921_id,
>
> base-commit: 57573ace0c1b142433dfe3d63ebf375269c80fc1
> --
> 2.43.0
>
Best regards,
Matteo Martelli
