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Message-ID: <81462799-6ef6-4079-9ebe-5b886d6e1eab@roeck-us.net>
Date: Wed, 2 Apr 2025 15:18:03 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: "William A. Kennington III" <william@...nnington.com>,
Jean Delvare <jdelvare@...e.com>
Cc: linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hwmon: (pmbus): Introduce page_change_delay
On 4/2/25 12:34, William A. Kennington III wrote:
> We have some buggy pmbus devices that require a delay after performing a
> page change operation before trying to issue more commands to the
> device.
>
> This allows for a configurable delay after page changes, but not
> affecting other read or write operations.
>
> Signed-off-by: William A. Kennington III <william@...nnington.com>
> ---
> drivers/hwmon/pmbus/pmbus.h | 1 +
> drivers/hwmon/pmbus/pmbus_core.c | 59 ++++++++++++++++++++++----------
> 2 files changed, 41 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/hwmon/pmbus/pmbus.h b/drivers/hwmon/pmbus/pmbus.h
> index ddb19c9726d6..742dafc44390 100644
> --- a/drivers/hwmon/pmbus/pmbus.h
> +++ b/drivers/hwmon/pmbus/pmbus.h
> @@ -482,6 +482,7 @@ struct pmbus_driver_info {
> */
> int access_delay; /* in microseconds */
> int write_delay; /* in microseconds */
> + int page_change_delay; /* in microseconds */
> };
>
> /* Regulator ops */
> diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
> index 787683e83db6..cfb724a8718b 100644
> --- a/drivers/hwmon/pmbus/pmbus_core.c
> +++ b/drivers/hwmon/pmbus/pmbus_core.c
> @@ -116,6 +116,7 @@ struct pmbus_data {
> int vout_high[PMBUS_PAGES]; /* voltage high margin */
> ktime_t write_time; /* Last SMBUS write timestamp */
> ktime_t access_time; /* Last SMBUS access timestamp */
> + ktime_t page_change_time; /* Last SMBUS page change timestamp */
> };
>
> struct pmbus_debugfs_entry {
> @@ -178,24 +179,44 @@ static void pmbus_wait(struct i2c_client *client)
>
> if (delta < info->access_delay)
> fsleep(info->access_delay - delta);
> - } else if (info->write_delay) {
> + }
> + if (info->write_delay) {
> delta = ktime_us_delta(ktime_get(), data->write_time);
>
> if (delta < info->write_delay)
> fsleep(info->write_delay - delta);
> }
> + if (info->page_change_delay) {
> + delta = ktime_us_delta(ktime_get(), data->page_change_time);
> +
page_change_time isn't actually set. I suggest to just use data->write_time.
Also see below.
> + if (delta < info->page_change_delay)
> + fsleep(info->page_change_delay - delta);
> + }
> }
>
> -/* Sets the last accessed timestamp for pmbus_wait */
> -static void pmbus_update_ts(struct i2c_client *client, bool write_op)
> +#define PMBUS_OP_READ_BIT 1
> +#define PMBUS_OP_WRITE_BIT 2
> +#define PMBUS_OP_PAGE_CHANGE_BIT 4
#define<space>NAME<tab>BIT(...)
> +
> +#define PMBUS_OP_READ PMBUS_OP_READ_BIT
> +#define PMBUS_OP_WRITE PMBUS_OP_WRITE_BIT
> +#define PMBUS_OP_PAGE_CHANGE (PMBUS_OP_PAGE_CHANGE_BIT | PMBUS_OP_WRITE)
That is way too complicated. Just make it
#define PMBUS_OP_READ BIT(0)
#define PMBUS_OP_WRITE BIT(1)
#define PMBUS_OP_PAGE_CHANGE BIT(2)
A page change implies a write, so it is not necessary to combine the bits.
> +
> +/* Sets the last operation timestamp for pmbus_wait */
> +static void pmbus_update_ts(struct i2c_client *client, int op)
> {
> struct pmbus_data *data = i2c_get_clientdata(client);
> const struct pmbus_driver_info *info = data->info;
> + ktime_t now = ktime_get();
>
> if (info->access_delay) {
> - data->access_time = ktime_get();
> - } else if (info->write_delay && write_op) {
> - data->write_time = ktime_get();
> + data->access_time = now;
> + }
> + if (info->write_delay && (op & PMBUS_OP_WRITE_BIT)) {
> + data->write_time = now;
> + }
> + if (info->page_change_delay && (op & PMBUS_OP_PAGE_CHANGE_BIT)) {
> + data->write_time = now;
> }
Seems to me that we should only need write_time and not
page_change_time since both will always be set together.
I also think this can be simplified if ktime_get() is always called anyway.
ktime_t now = ktime_get();
data->access_time = now;
if (op & (PMBUS_OP_WRITE | PMBUS_OP_PAGE_CHANGE))
data->write_time = now;
It doesn't matter if the values are set unnecessarily if there is no delay
because they won't be used in that case.
> }
>
> @@ -211,13 +232,13 @@ int pmbus_set_page(struct i2c_client *client, int page, int phase)
> data->info->pages > 1 && page != data->currpage) {
> pmbus_wait(client);
> rv = i2c_smbus_write_byte_data(client, PMBUS_PAGE, page);
> - pmbus_update_ts(client, true);
> + pmbus_update_ts(client, PMBUS_OP_PAGE_CHANGE);
> if (rv < 0)
> return rv;
>
> pmbus_wait(client);
> rv = i2c_smbus_read_byte_data(client, PMBUS_PAGE);
> - pmbus_update_ts(client, false);
> + pmbus_update_ts(client, PMBUS_OP_READ);
> if (rv < 0)
> return rv;
>
> @@ -231,7 +252,7 @@ int pmbus_set_page(struct i2c_client *client, int page, int phase)
> pmbus_wait(client);
> rv = i2c_smbus_write_byte_data(client, PMBUS_PHASE,
> phase);
> - pmbus_update_ts(client, true);
> + pmbus_update_ts(client, PMBUS_OP_WRITE);
> if (rv)
> return rv;
> }
> @@ -251,7 +272,7 @@ int pmbus_write_byte(struct i2c_client *client, int page, u8 value)
>
> pmbus_wait(client);
> rv = i2c_smbus_write_byte(client, value);
> - pmbus_update_ts(client, true);
> + pmbus_update_ts(client, PMBUS_OP_WRITE);
>
> return rv;
> }
> @@ -286,7 +307,7 @@ int pmbus_write_word_data(struct i2c_client *client, int page, u8 reg,
>
> pmbus_wait(client);
> rv = i2c_smbus_write_word_data(client, reg, word);
> - pmbus_update_ts(client, true);
> + pmbus_update_ts(client, PMBUS_OP_WRITE);
>
> return rv;
> }
> @@ -408,7 +429,7 @@ int pmbus_read_word_data(struct i2c_client *client, int page, int phase, u8 reg)
>
> pmbus_wait(client);
> rv = i2c_smbus_read_word_data(client, reg);
> - pmbus_update_ts(client, false);
> + pmbus_update_ts(client, PMBUS_OP_READ);
>
> return rv;
> }
> @@ -471,7 +492,7 @@ int pmbus_read_byte_data(struct i2c_client *client, int page, u8 reg)
>
> pmbus_wait(client);
> rv = i2c_smbus_read_byte_data(client, reg);
> - pmbus_update_ts(client, false);
> + pmbus_update_ts(client, PMBUS_OP_READ);
>
> return rv;
> }
> @@ -487,7 +508,7 @@ int pmbus_write_byte_data(struct i2c_client *client, int page, u8 reg, u8 value)
>
> pmbus_wait(client);
> rv = i2c_smbus_write_byte_data(client, reg, value);
> - pmbus_update_ts(client, true);
> + pmbus_update_ts(client, PMBUS_OP_WRITE);
>
> return rv;
> }
> @@ -523,7 +544,7 @@ static int pmbus_read_block_data(struct i2c_client *client, int page, u8 reg,
>
> pmbus_wait(client);
> rv = i2c_smbus_read_block_data(client, reg, data_buf);
> - pmbus_update_ts(client, false);
> + pmbus_update_ts(client, PMBUS_OP_READ);
>
> return rv;
> }
> @@ -2530,7 +2551,7 @@ static int pmbus_read_coefficients(struct i2c_client *client,
> rv = i2c_smbus_xfer(client->adapter, client->addr, client->flags,
> I2C_SMBUS_WRITE, PMBUS_COEFFICIENTS,
> I2C_SMBUS_BLOCK_PROC_CALL, &data);
> - pmbus_update_ts(client, true);
> + pmbus_update_ts(client, PMBUS_OP_READ | PMBUS_OP_WRITE);
I don't immediately follow the reason for adding PMBUS_OP_READ.
>
> if (rv < 0)
> return rv;
> @@ -2734,7 +2755,7 @@ static int pmbus_init_common(struct i2c_client *client, struct pmbus_data *data,
> if (!(data->flags & PMBUS_NO_CAPABILITY)) {
> pmbus_wait(client);
> ret = i2c_smbus_read_byte_data(client, PMBUS_CAPABILITY);
> - pmbus_update_ts(client, false);
> + pmbus_update_ts(client, PMBUS_OP_READ);
>
> if (ret >= 0 && (ret & PB_CAPABILITY_ERROR_CHECK)) {
> if (i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_PEC))
> @@ -2750,13 +2771,13 @@ static int pmbus_init_common(struct i2c_client *client, struct pmbus_data *data,
> data->read_status = pmbus_read_status_word;
> pmbus_wait(client);
> ret = i2c_smbus_read_word_data(client, PMBUS_STATUS_WORD);
> - pmbus_update_ts(client, false);
> + pmbus_update_ts(client, PMBUS_OP_READ);
>
> if (ret < 0 || ret == 0xffff) {
> data->read_status = pmbus_read_status_byte;
> pmbus_wait(client);
> ret = i2c_smbus_read_byte_data(client, PMBUS_STATUS_BYTE);
> - pmbus_update_ts(client, false);
> + pmbus_update_ts(client, PMBUS_OP_READ);
>
> if (ret < 0 || ret == 0xff) {
> dev_err(dev, "PMBus status register not found\n");
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