On 3/25/19 1:21 AM, Lei YU wrote:
This email is to ask/discuss if there is a stable path/name (or whatever) for
hwmon devices in the different versions of kernels.
In OpenBMC, the service phosphor-hwmon reads the sensors' value and expose to
DBus, depending on a configure file that matches the device tree path.
The service is started by udev rule, called with the DEVPATH and OF_FULLNAME,
so it knows where to find the configure file depending on DEVPATH or
OF_FULLNAME.
E.g. on Romulus BMC, the w83773 sensor has OF_FULLNAME at
/ahb/apb/i2c@1e78a000/i2c-bus@440/w83773g@4c,
and the service knows the config is matched from path
/etc/default/obmc/hwmon/ahb/apb/i2c@1e78a000/i2c-bus@440/w83773g@xxxxxxx
However, the DEVPATH or OF_FULLNAME is not stable in different kernels:
* In 4.1x kernel, the path is as above.
* In 5.0 kernel, "i2c@1e78a000" is changed to "bus@1e78a000" in the path.
This is due to a devicetree source change with commit 1426d40e11f73 ("ARM: dts:
aspeed: Fix I2C bus warnings"). In general you can not assume that devicetree
files (or path names derived from devicetree source files) stay the same across
kernel releases.
This breaks the userspace's phosphor-hwmon.
If we fix the issue by updating the configure files' path in userspace, it
means the userspace only with the new 5.x kernel.
So the question here is, it there a stable way for userspace to match a hwmon
device?
libsensors should handle it for you, but I don't immediately know how to map
that into udev rules. Jean, any idea ?
Guenter
