linux-kernel - Re: [PATCH v3 2/2] PCI: Add support for Enhanced Allocation devices

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Date:	Wed, 30 Sep 2015 15:50:11 -0700
From:	"Sean O. Stalley" <sean.stalley@...el.com>
To:	David Daney <ddaney@...iumnetworks.com>
Cc:	David Daney <ddaney.cavm@...il.com>, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Rafał Miłecki <zajec5@...il.com>,
	linux-api@...r.kernel.org, yinghai@...nel.org,
	rajatxjain@...il.com, gong.chen@...ux.intel.com,
	David Daney <david.daney@...ium.com>
Subject: Re: [PATCH v3 2/2] PCI: Add support for Enhanced Allocation devices

On Tue, Sep 29, 2015 at 04:53:20PM -0700, David Daney wrote:
> On 09/29/2015 03:47 PM, Sean O. Stalley wrote:
> [...]
> >>>>diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> >>>>index 6a9a111..7c60b16 100644
> >>>>--- a/drivers/pci/pci.c
> >>>>+++ b/drivers/pci/pci.c
> >>>>@@ -2148,6 +2148,284 @@ void pci_pm_init(struct pci_dev *dev)
> >>>>  	}
> >>>>  }
> >>>>
> >>>>+static unsigned long pci_ea_set_flags(struct pci_dev *dev, u8 prop)
> >>>>+{
> >>>>+	unsigned long flags = IORESOURCE_PCI_FIXED | IORESOURCE_SIZEALIGN;
> >>>
> >>>Why did you add the IORESOURCE_SIZEALIGN flag? EA allows for unaligned resources.
> >>
> >>pci_bus_assign_resources() fails causing the devices to be unusable
> >>if resource_alignment() returns zero.  The easiest fix for this was
> >>to specify IORESOURCE_SIZEALIGN.
> >>
> >>An alternative would be to change the code in setup-bus.c so that
> >>for IORESOURCE_PCI_FIXED resources, it didn't barf.
> >
> >I would do this alternative, but with a IORESOURCE_PCI_EA flag.
> >
> 
> I don't think we need IORESOURCE_PCI_EA.  If a resource is tagged as
> IORESOURCE_PCI_FIXED that means that it cannot be changed, we
> shouldn't care why it is fixed (due to an EA capability for
> example).  We just need to gracefully handle IORESOURCE_PCI_FIXED in
> the places where things currently go wrong.
> 
> David Daney
> 

I agree that we need to make sure fixed things stay fixed,
regardless of if they are fixed by EA or something else.

The question is: do we want to allow all fixed resources to be non-aligned, or just EA?

-Sean
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