linux-kernel - Re: [PATCH 3/3] PCI: Set pref for mem64 resource of pcie device

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Date:	Thu, 09 Apr 2015 18:56:55 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	David Miller <davem@...emloft.net>,
	David Ahern <david.ahern@...cle.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH 3/3] PCI: Set pref for mem64 resource of pcie device

On Wed, 2015-04-08 at 21:11 -0700, Yinghai Lu wrote:
> That way should be more intrusive to current code, as we are using
> type_mask checking to share the code among
> parent(pref)/child(pref), parent(no-pref)/child(pref), and
> parent(no-pref)/child(pref)

That's fine, as long as the helper knows which one is the parent and
which one is the child.

In fact, as "cute" as the mask trick is, I think it would generally make
the code more self explanatory if it explicitly tested for the
combinations that are supported, ie something like

	if (parent_is_pref && !child_is_pref && child->pcie_only)
		...
	else if (!parent_is_pref)
		...
etc...

The impact in performance would be in the noise and the logic of the
algorithm a LOT more explicit.

Cheers,
Ben.


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