Re: [GIT PATCH] More PCI patches for 2.6.13

[Alan Stern <stern@rowland.harvard.edu>]

On Fri, 9 Sep 2005, Linus Torvalds wrote:
> 
> On Fri, 9 Sep 2005, Linus Torvalds wrote:
> > 
> > There are functions where it is really _important_ to check the error 
> > return, because they return errors often enough - and the error case is 
> > something you have to do something about - that it's good to force people 
> > to be aware.
> > 
> > But "pci_set_power_state()"?
> > 
> > I don't think so.
> 
> Btw, a perfect example of this is
> 
> 	pci_set_power_state(pdev, 0);
> 
> which is a very common thing to do in a driver init routine. And it has
> absolutely _no_ valid return values: it either succeeds, or it doesn't,
> and the only reason it wouldn't succeed is because the device doesn't
> support power management in the first place (in which case it already
> effectively is in state 0).
> 
> In other words, there's nothing you can or should do about it. Testing the 
> return value is pointless. And thus adding a "must_check" is really really 
> wrong: it might make people do
> 
> 	if (pci_set_power_state(pdev, 0))
> 		return -ENODEV
> 
> which is actually actively the _wrong_ thing to do, and would just cause 
> old revisions of the chip that might not support PM capabilities to no 
> longer work.

Funny you should say this -- exactly that problem _did_ arise.  See

http://marc.theaimsgroup.com/?l=linux-pci&m=112621842604724&w=2

pci_enable_device_bars() would an error when trying to initialize 
devices without PM support, because it started checking the return value
from pci_set_power_state().

Alan Stern

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