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SubjectRe: [PATCH 1/2] [PCI] Check that MWI bit really did get set
On Mon, 16 Oct 2006 01:02:40 +0100
Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:

> Ar Sul, 2006-10-15 am 16:18 -0700, ysgrifennodd Andrew Morton:
> > No. If pci_set_mwi() detects an unexpected error then the driver should
> > take some action: report it, recover from it, fail to load, etc. If the
> > driver fails to do any of this then it's a buggy driver.
>
> Wrong and there are several drivers in the kernel that are proof of
> this.

Let me restore the words from my earlier email which you removed so that
you could say that:

For you the driver author to make assumptions about what's happening
inside pci_set_mwi() is a layering violation. Maybe the bridge got
hot-unplugged. Maybe the attempt to set MWI caused some synchronous PCI
error. For example, take a look at the various implementations of
pci_ops.read() around the place - various of them can fail for various
reasons.


> > You, the driver author _do not know_ what pci_set_mwi() does at present, on
> > all platforms, nor do you know what it does in the future. For you the
>
> You don't care. It isn't an error for set_mwi to fail. In fact the only
> reason set_mwi even needs to bother with a return code is that some
> chips want you to set other config private to the device if it is
> available and active.
>

Let me restore the words from my earlier email which you removed which
address that:

Now it could be that an appropriate solution is to make pci_set_mwi()
return only 0 or 1, and to generate a warning from within pci_set_mwi()
if some unexpected error happens. In which case it is legitimate for
callers to not check for errors.


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