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hwmon: (pmbus) Initialise page count in pmbus_identify()

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[ Upstream commit 6b6e2e8fd0de3fa7c6f4f8fe6841b01770b2e7bc ]

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>
Fixes: 442aba7872 ("hwmon: PMBus device driver")
Link: https://lore.kernel.org/r/20250227222455.2583468-1-titusr@google.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Titus Rwantare 2025-02-27 22:24:55 +00:00 committed by Greg Kroah-Hartman
parent 29e0cd296c
commit afaf7f4516
1 changed files with 2 additions and 0 deletions
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2
drivers/hwmon/pmbus/pmbus.c
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@ -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;