[systemd-devel] [PATCH 1/3] rules: Enable runtime device power management on Intel HDA controllers

[Matthew Garrett]

(Resending from the correct address)

On Sat, Apr 18, 2015 at 07:51:26PM +0200, Kay Sievers wrote:

> It looks like an unconditional static assignment.
> 
> 
> Why should udev carry this? We generally do not want to do things like
> that. Udev can help if there is conditional policy or complex
> cross-subsystem knowledge is needed, but this looks just like a job
> for the kernel and not userspace.

1) having this in udev makes it easier for users to alter the 
configuration - the kernel can then afford to be conservative until we 
enable power management, rather than potentially breaking the device the 
moment pm is enabled without any ability to recover it.

2) this config is currently static, but the appropriate policy may turn 
out to be more complicated in some scenarios (interactions between 
devices and their upstream bridges, for instance, or USB Bluetooth 
controllers that are on-die with a PCI wifi controller without having a 
common exposed bus topology yet still having pm interactions). Splitting 
this between udev and the kernel makes it more difficult to determine 
the source of the policy and debug it.

3) we already have examples of this in udev, so people already expect to 
find it here. 

-- 
Matthew Garrett | mjg59 at srcf.ucam.org