linux-kernel - Re: [PATCH v4 9/9] PCI/MSI: Introduce pci_auto_enable

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Message-ID: <20131219134719.GA16994@htj.dyndns.org>
Date:	Thu, 19 Dec 2013 08:47:19 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Alexander Gordeev <agordeev@...hat.com>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Michael Ellerman <michael@...erman.id.au>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ben Hutchings <bhutchings@...arflare.com>,
	David Laight <David.Laight@...lab.com>,
	Mark Lord <kernel@...rt.ca>, "H. Peter Anvin" <hpa@...or.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [PATCH v4 9/9] PCI/MSI: Introduce pci_auto_enable_msi*() family
 helpers

Hello,

On Thu, Dec 19, 2013 at 02:42:45PM +0100, Alexander Gordeev wrote:
> I have troubles with this fallback logic. On each failed step we get an
> error and we do not know if this is indeed an error or an indication of
> insufficient MSI resources. Even -ENOSPC would not tell much, since it
> could be thrown from a lower level.

Well, it's not hard to define what -ENOSPC should mean.

> By contrast, with the tri-state return value we can distinguish and bail
> out on errors right away.

I kinda like that the available options are listed explicitly on the
caller side (even if it ends up being a loop).  It decreases the
chance of the caller going "oh I didn't expect _that_" and generaly
makes things easier to follow.

> So the above is bit ungraceful for me. Combined with a possible waste in
> logs (if we're hitting the same error) it is quite enough for me to keep
> current the interfaces, at least for a time being.

FWIW, I like Bjorn's suggestion.  Given that this is mostly corner
case thing, it isn't as important as the common ones but we might as
well while we're at it.

Thanks a lot for your work in the area!  :)

-- 
tejun
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