hwmon: Add driver for fsp-3y PSUs and PDUs

This patch adds support for these devices:
- YH-5151E - the PDU
- YM-2151E - the PSU

The device datasheet says that the devices support PMBus 1.2, but in my
testing, a lot of the commands aren't supported and if they are, they
sometimes behave strangely or inconsistently. For example, writes to the
PAGE command requires using PEC, otherwise the write won't work and the
page won't switch, even though, the standard says that PEC is optional.
On the other hand, writes to SMBALERT don't require PEC. Because of
this, the driver is mostly reverse engineered with the help of a tool
called pmbus_peek written by David Brownell (and later adopted by my
colleague Jan Kundrát).

The device also has some sort of a timing issue when switching pages,
which is explained further in the code.

Because of this, the driver support is limited. It exposes only the
values that have been tested to work correctly.

Signed-off-by: Václav Kubernát <kubernat@cesnet.cz>
Link: https://lore.kernel.org/r/20210414080019.3530794-1-kubernat@cesnet.cz
[groeck: Fixed up "missing braces around initializer" from 0-day]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

1 files changed, 10 insertions, 0 deletions

diff --git a/drivers/hwmon/pmbus/Kconfig b/drivers/hwmon/pmbus/Kconfig
index fd0911017be6..e9727176b167 100644
--- a/drivers/hwmon/pmbus/Kconfig
+++ b/drivers/hwmon/pmbus/Kconfig
@@ -65,6 +65,16 @@ config SENSORS_BPA_RS600
 	  This driver can also be built as a module. If so, the module will
 	  be called bpa-rs600.
 
+config SENSORS_FSP_3Y
+	tristate "FSP/3Y-Power power supplies"
+	help
+	  If you say yes here you get hardware monitoring support for
+	  FSP/3Y-Power hot-swap power supplies.
+	  Supported models: YH-5151E, YM-2151E
+
+	  This driver can also be built as a module. If so, the module will
+	  be called fsp-3y.
+
 config SENSORS_IBM_CFFPS
 	tristate "IBM Common Form Factor Power Supply"
 	depends on LEDS_CLASS