[PATCH] hwmon: (pmbus) Initialise page count in pmbus_identify()

[PATCH] hwmon: (pmbus) Initialise page count in pmbus_identify()

[Titus Rwantare]

The `pmbus_identify()` function fails to correctly determine the number
of supported pages on PMBus devices. This occurs because `info->pages`
is implicitly zero-initialised, and `pmbus_set_page()` does not perform
writes to the page register if `info->pages` is not yet initialised.
Without this patch, `info->pages` is always set to the maximum after
scanning.

This patch initialises `info->pages` to `PMBUS_PAGES` before the probing
loop, enabling `pmbus_set_page()` writes to make it out onto the bus
correctly identifying the number of pages. `PMBUS_PAGES` seemed like a
reasonable non-zero number because that's the current result of the
identification process.

Testing was done with a PMBus device in QEMU.

Signed-off-by: Titus Rwantare <titusr@google.com>
---
 drivers/hwmon/pmbus/pmbus.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/hwmon/pmbus/pmbus.c b/drivers/hwmon/pmbus/pmbus.c
index 77cf268e7d2d..920cd5408141 100644
--- a/drivers/hwmon/pmbus/pmbus.c
+++ b/drivers/hwmon/pmbus/pmbus.c
@@ -103,6 +103,8 @@ static int pmbus_identify(struct i2c_client *client,
 		if (pmbus_check_byte_register(client, 0, PMBUS_PAGE)) {
 			int page;
 
+			info->pages = PMBUS_PAGES;
+
 			for (page = 1; page < PMBUS_PAGES; page++) {
 				if (pmbus_set_page(client, page, 0xff) < 0)
 					break;
-- 
2.48.1.711.g2feabab25a-goog

Re: [PATCH] hwmon: (pmbus) Initialise page count in pmbus_identify()

[Guenter Roeck]

On Thu, Feb 27, 2025 at 10:24:55PM +0000, Titus Rwantare wrote:
> The `pmbus_identify()` function fails to correctly determine the number
> of supported pages on PMBus devices. This occurs because `info->pages`
> is implicitly zero-initialised, and `pmbus_set_page()` does not perform
> writes to the page register if `info->pages` is not yet initialised.
> Without this patch, `info->pages` is always set to the maximum after
> scanning.
> 
> This patch initialises `info->pages` to `PMBUS_PAGES` before the probing
> loop, enabling `pmbus_set_page()` writes to make it out onto the bus
> correctly identifying the number of pages. `PMBUS_PAGES` seemed like a
> reasonable non-zero number because that's the current result of the
> identification process.
> 
> Testing was done with a PMBus device in QEMU.
> 
> Signed-off-by: Titus Rwantare <titusr@google.com>

Applied.

Thanks,
Guenter