Re: [PATCH net-next v4 2/2] net: dsa: microchip: Add drive strength configuration

From: Vladimir Oltean
Date: Tue Sep 12 2023 - 07:37:07 EST

On Tue, Sep 12, 2023 at 06:54:59AM +0200, Oleksij Rempel wrote:
> Add device tree based drive strength configuration support. It is needed to
> pass EMI validation on our hardware.
>
> Configuration values are based on the vendor's reference driver.
>
> Tested on KSZ9563R.
>
> Signed-off-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx>
> Reviewed-by: Andrew Lunn <andrew@xxxxxxx>
> ---
> drivers/net/dsa/microchip/ksz8795_reg.h | 14 --
> drivers/net/dsa/microchip/ksz9477_reg.h | 13 -
> drivers/net/dsa/microchip/ksz_common.c | 309 ++++++++++++++++++++++++
> drivers/net/dsa/microchip/ksz_common.h | 20 ++
> 4 files changed, 329 insertions(+), 27 deletions(-)
>
> diff --git a/drivers/net/dsa/microchip/ksz_common.c b/drivers/net/dsa/microchip/ksz_common.c
> index 42db7679c3606..ee77c44e99f65 100644
> --- a/drivers/net/dsa/microchip/ksz_common.c
> +++ b/drivers/net/dsa/microchip/ksz_common.c
> @@ -186,6 +186,72 @@ static const struct ksz_mib_names ksz9477_mib_names[] = {
> { 0x83, "tx_discards" },
> };
>
> +struct ksz_driver_strength_prop {
> + const char *name;
> + int offset;
> + int value;
> +};
> +
> +enum ksz_driver_strength_type {
> + KSZ_DRIVER_STRENGTH_HI,
> + KSZ_DRIVER_STRENGTH_LO,
> + KSZ_DRIVER_STRENGTH_IO,
> +};
> +
> +/**
> + * struct ksz_drive_strength - drive strength mapping
> + * @reg_val: register value
> + * @milliamp: milliamp value
> + */
> +struct ksz_drive_strength {
> + u32 reg_val;
> + u32 milliamp;
> +};
> +
> +/* ksz9477_drive_strengths - Drive strength mapping for KSZ9477 variants
> + *
> + * This values are not documented in KSZ9477 variants but confirmed by
> + * Microchip that KSZ9477, KSZ9567, KSZ8567, KSZ9897, KSZ9896, KSZ9563, KSZ9893
> + * and KSZ8563 are using same register (drive strength) settings like KSZ8795.
> + *
> + * Documentation in KSZ8795CLX provides more information with some
> + * recommendations:
> + * - for high speed signals
> + * 1. 4 mA or 8 mA is often used for MII, RMII, and SPI interface with using
> + * 2.5V or 3.3V VDDIO.
> + * 2. 12 mA or 16 mA is often used for MII, RMII, and SPI interface with
> + * using 1.8V VDDIO.
> + * 3. 20 mA or 24 mA is often used for GMII/RGMII interface with using 2.5V
> + * or 3.3V VDDIO.
> + * 4. 28 mA is often used for GMII/RGMII interface with using 1.8V VDDIO.
> + * 5. In same interface, the heavy loading should use higher one of the
> + * drive current strength.
> + * - for low speed signals
> + * 1. 3.3V VDDIO, use either 4 mA or 8 mA.
> + * 2. 2.5V VDDIO, use either 8 mA or 12 mA.
> + * 3. 1.8V VDDIO, use either 12 mA or 16 mA.
> + * 4. If it is heavy loading, can use higher drive current strength.
> + */
> +static const struct ksz_drive_strength ksz9477_drive_strengths[] = {
> + { SW_DRIVE_STRENGTH_2MA, 2000 },
> + { SW_DRIVE_STRENGTH_4MA, 4000 },
> + { SW_DRIVE_STRENGTH_8MA, 8000 },
> + { SW_DRIVE_STRENGTH_12MA, 12000 },
> + { SW_DRIVE_STRENGTH_16MA, 16000 },
> + { SW_DRIVE_STRENGTH_20MA, 20000 },
> + { SW_DRIVE_STRENGTH_24MA, 24000 },
> + { SW_DRIVE_STRENGTH_28MA, 28000 },
> +};
> +
> +/* ksz8830_drive_strengths - Drive strength mapping for KSZ8830, KSZ8873, ..
> + * variants.
> + * This values are documented in KSZ8873 and KSZ8863 datasheets.
> + */
> +static const struct ksz_drive_strength ksz8830_drive_strengths[] = {
> + { 0, 8000 },
> + { KSZ8873_DRIVE_STRENGTH_16MA, 16000 },
> +};
> +
> static const struct ksz_dev_ops ksz8_dev_ops = {
> .setup = ksz8_setup,
> .get_port_addr = ksz8_get_port_addr,
> @@ -3530,6 +3596,245 @@ static void ksz_parse_rgmii_delay(struct ksz_device *dev, int port_num,
> dev->ports[port_num].rgmii_tx_val = tx_delay;
> }
>
> +/**
> + * ksz_drive_strength_to_reg() - Convert drive strength value to corresponding
> + * register value.
> + * @array: The array of drive strength values to search.
> + * @array_size: The size of the array.
> + * @milliamp: The drive strength value in milliamp to be converted.
> + *
> + * This function searches the array of drive strength values for the given
> + * milliamp value and returns the corresponding register value for that drive.
> + *
> + * Returns: If found, the corresponding register value for that drive strength
> + * is returned. Otherwise, -EINVAL is returned indicating an invalid value.
> + */
> +static int ksz_drive_strength_to_reg(const struct ksz_drive_strength *array,
> + size_t array_size, int milliamp)
> +{
> + int i;
> +
> + for (i = 0; i < array_size; i++) {
> + if (array[i].milliamp == milliamp)
> + return array[i].reg_val;
> + }
> +
> + return -EINVAL;
> +}
> +
> +/**
> + * ksz_drive_strength_error() - Report invalid drive strength value
> + * @dev: ksz device
> + * @array: The array of drive strength values to search.
> + * @array_size: The size of the array.
> + * @milliamp: Invalid drive strength value in milliamp
> + *
> + * This function logs an error message when an unsupported drive strength value
> + * is detected. It lists out all the supported drive strength values for
> + * reference in the error message.
> + */
> +static void ksz_drive_strength_error(struct ksz_device *dev,
> + const struct ksz_drive_strength *array,
> + size_t array_size, int milliamp)
> +{
> + char supported_values[100];
> + size_t remaining_size;
> + int added_len;
> + char *ptr;
> + int i;
> +
> + remaining_size = sizeof(supported_values);
> + ptr = supported_values;
> +
> + for (i = 0; i < array_size; i++) {
> + added_len = snprintf(ptr, remaining_size,
> + i == 0 ? "%d" : ", %d", array[i].milliamp);
> +
> + if (added_len < 0 || added_len >= remaining_size)
> + break;
> +
> + ptr += added_len;
> + remaining_size -= added_len;
> + }
> +
> + dev_err(dev->dev, "Invalid drive strength %d, supported values are %s\n",
> + milliamp, supported_values);
> +}

Milliamp or microamp? The dt-binding is in microamps, and I see no micro -> milli
conversion.

> +
> +/**
> + * ksz9477_drive_strength_write() - Set the drive strength for specific KSZ9477
> + * chip variants.
> + * @dev: ksz device
> + * @props: Array of drive strength properties to be applied
> + * @num_props: Number of properties in the array
> + *
> + * This function configures the drive strength for various KSZ9477 chip variants
> + * based on the provided properties. It handles chip-specific nuances and
> + * ensures only valid drive strengths are written to the respective chip.
> + *
> + * Return: 0 on successful configuration, a negative error code on failure.
> + */
> +static int ksz9477_drive_strength_write(struct ksz_device *dev,
> + struct ksz_driver_strength_prop *props,
> + int num_props)
> +{
> + size_t array_size = ARRAY_SIZE(ksz9477_drive_strengths);
> + int i, ret, reg;
> + u8 mask = 0;
> + u8 val = 0;
> +
> + if (props[KSZ_DRIVER_STRENGTH_IO].value != -1)
> + dev_warn(dev->dev, "%s is not supported by this chip variant\n",
> + props[KSZ_DRIVER_STRENGTH_IO].name);
> +
> + if (dev->chip_id == KSZ8795_CHIP_ID ||
> + dev->chip_id == KSZ8794_CHIP_ID ||
> + dev->chip_id == KSZ8765_CHIP_ID)
> + reg = KSZ8795_REG_SW_CTRL_20;
> + else
> + reg = KSZ9477_REG_SW_IO_STRENGTH;
> +
> + for (i = 0; i < num_props; i++) {
> + if (props[i].value == -1)
> + continue;
> +
> + ret = ksz_drive_strength_to_reg(ksz9477_drive_strengths,
> + array_size, props[i].value);
> + if (ret < 0) {
> + ksz_drive_strength_error(dev, ksz9477_drive_strengths,
> + array_size, props[i].value);
> + return ret;
> + }
> +
> + mask |= SW_DRIVE_STRENGTH_M << props[i].offset;
> + val |= ret << props[i].offset;
> + }
> +
> + return ksz_rmw8(dev, reg, mask, val);
> +}
> +
> +/**
> + * ksz8830_drive_strength_write() - Set the drive strength configuration for
> + * KSZ8830 compatible chip variants.
> + * @dev: ksz device
> + * @props: Array of drive strength properties to be set
> + * @num_props: Number of properties in the array
> + *
> + * This function applies the specified drive strength settings to KSZ8830 chip
> + * variants (KSZ8873, KSZ8863).
> + * It ensures the configurations align with what the chip variant supports and
> + * warns or errors out on unsupported settings.
> + *
> + * Return: 0 on success, error code otherwise
> + */
> +static int ksz8830_drive_strength_write(struct ksz_device *dev,
> + struct ksz_driver_strength_prop *props,
> + int num_props)
> +{
> + size_t array_size = ARRAY_SIZE(ksz8830_drive_strengths);
> + int milliamp;
> + int i, ret;
> +
> + for (i = 0; i < num_props; i++) {
> + if (props[i].value == -1 || i == KSZ_DRIVER_STRENGTH_IO)
> + continue;
> +
> + dev_warn(dev->dev, "%s is not supported by this chip variant\n",
> + props[i].name);
> + }
> +
> + milliamp = props[KSZ_DRIVER_STRENGTH_IO].value;
> + ret = ksz_drive_strength_to_reg(ksz8830_drive_strengths, array_size,
> + milliamp);
> + if (ret < 0) {
> + ksz_drive_strength_error(dev, ksz8830_drive_strengths,
> + array_size, milliamp);
> + return ret;
> + }
> +
> + return ksz_rmw8(dev, KSZ8873_REG_GLOBAL_CTRL_12,
> + KSZ8873_DRIVE_STRENGTH_16MA, ret);
> +}
> +
> +/**
> + * ksz_parse_drive_strength() - Extract and apply drive strength configurations
> + * from device tree properties.
> + * @dev: ksz device
> + *
> + * This function reads the specified drive strength properties from the
> + * device tree, validates against the supported chip variants, and sets
> + * them accordingly. An error should be critical here, as the drive strength
> + * settings are crucial for EMI compliance.
> + *
> + * Return: 0 on success, error code otherwise
> + */
> +static int ksz_parse_drive_strength(struct ksz_device *dev)
> +{
> + struct ksz_driver_strength_prop of_props[] = {
> + [KSZ_DRIVER_STRENGTH_HI] = {
> + .name = "microchip,hi-drive-strength-microamp",
> + .offset = SW_HI_SPEED_DRIVE_STRENGTH_S,
> + .value = -1

nit: it is usual to place a comma even after the last element of an
array or structure, because it makes future patches cleaner (they don't
need to touch the previous line to add a comma).

> + },
> + [KSZ_DRIVER_STRENGTH_LO] = {
> + .name = "microchip,lo-drive-strength-microamp",
> + .offset = SW_LO_SPEED_DRIVE_STRENGTH_S,
> + .value = -1
> + },
> + [KSZ_DRIVER_STRENGTH_IO] = {
> + .name = "microchip,io-drive-strength-microamp",
> + .offset = 0, /* don't care */
> + .value = -1
> + },
> + };
> + struct device_node *np = dev->dev->of_node;
> + bool found = false;
> + int i, ret;
> +
> + for (i = 0; i < ARRAY_SIZE(of_props); i++) {
> + ret = of_property_read_u32(np, of_props[i].name,
> + &of_props[i].value);
> + if (ret && ret != -EINVAL)
> + dev_warn(dev->dev, "Failed to read %s\n",
> + of_props[i].name);
> + if (ret)
> + continue;
> +
> + found = true;
> + }
> +
> + if (!found)
> + return 0;

Maybe "have_any_prop" would be a better name to avoid Christophe's confusion?

> +
> + switch (dev->chip_id) {
> + case KSZ8830_CHIP_ID:
> + return ksz8830_drive_strength_write(dev, of_props,
> + ARRAY_SIZE(of_props));
> + case KSZ8795_CHIP_ID:
> + case KSZ8794_CHIP_ID:
> + case KSZ8765_CHIP_ID:
> + case KSZ8563_CHIP_ID:
> + case KSZ9477_CHIP_ID:
> + case KSZ9563_CHIP_ID:
> + case KSZ9567_CHIP_ID:
> + case KSZ9893_CHIP_ID:
> + case KSZ9896_CHIP_ID:
> + case KSZ9897_CHIP_ID:
> + return ksz9477_drive_strength_write(dev, of_props,
> + ARRAY_SIZE(of_props));
> + default:
> + for (i = 0; i < ARRAY_SIZE(of_props); i++) {
> + if (of_props[i].value == -1)
> + continue;
> +
> + dev_warn(dev->dev, "%s is not supported by this chip variant\n",
> + of_props[i].name);
> + }
> + }
> +
> + return 0;
> +}
> +