linux-kernel - Re: [RFT PATCH v3] PCI: move pci_read_bridge

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Date:	Wed, 22 Jul 2015 17:55:31 +0100
From:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Ralf Baechle <ralf@...ux-mips.org>,
	"James E.J. Bottomley" <jejb@...isc-linux.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Richard Henderson <rth@...ddle.net>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	David Howells <dhowells@...hat.com>,
	Russell King <linux@....linux.org.uk>,
	Tony Luck <tony.luck@...el.com>,
	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...hat.com>,
	Michal Simek <monstr@...str.eu>,
	Chris Zankel <chris@...kel.net>, Arnd Bergmann <arnd@...db.de>,
	Krzysztof Halasa <khalasa@...p.pl>,
	Phil Edworthy <phil.edworthy@...esas.com>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Jingoo Han <jg1.han@...sung.com>,
	Lucas Stach <l.stach@...gutronix.de>,
	Simon Horman <horms@...ge.net.au>,
	Minghuan Lian <minghuan.Lian@...escale.com>,
	Murali Karicheri <m-karicheri2@...com>,
	Tanmay Inamdar <tinamdar@....com>,
	Kishon Vijay Abraham I <kishon@...com>,
	Thierry Reding <thierry.reding@...il.com>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Will Deacon <Will.Deacon@....com>,
	Jayachandran C <jchandra@...adcom.com>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>
Subject: Re: [RFT PATCH v3] PCI: move pci_read_bridge_bases to the generic
 PCI layer

Hi Guenter,

On Wed, Jul 22, 2015 at 03:22:57PM +0100, Guenter Roeck wrote:
> On 07/22/2015 02:14 AM, Lorenzo Pieralisi wrote:
> > Bjorn, Guenter,
> >
> > On Thu, Jul 09, 2015 at 11:59:16AM +0100, Lorenzo Pieralisi wrote:
> >> When a PCI bus is scanned, upon PCI bridge detection the kernel
> >> has to read the bridge registers to set-up its resources so that
> >> the PCI resource hierarchy can be validated properly.
> >>
> >> Most if not all architectures read PCI bridge registers in the
> >> pcibios_fixup_bus hook, that is called by the PCI generic layer
> >> whenever a PCI bus is scanned.
> >>
> >> Since pci_read_bridge_bases is an arch agnostic operation (and it
> >> is carried out on all architectures) it can be moved to the generic
> >> PCI layer in order to consolidate code and remove the respective
> >> calls from the architectures back-ends.
> >>
> >> The PCI_PROBE_ONLY flag is not checked before calling
> >> pci_read_bridge_buses in the generic layer since reading the bridge
> >> bases is not related to resources assignment; this implies that it
> >> can be carried out safely on PCI_PROBE_ONLY systems too and should
> >> not affect architectures (alpha, mips) that check the PCI_PROBE_ONLY
> >> flag before reading the bridge bases.
> >>
> >> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> >> Cc: Ralf Baechle <ralf@...ux-mips.org>
> >> Cc: James E.J. Bottomley <jejb@...isc-linux.org>
> >> Cc: Michael Ellerman <mpe@...erman.id.au>
> >> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> >> Cc: Richard Henderson <rth@...ddle.net>
> >> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> >> Cc: David Howells <dhowells@...hat.com>
> >> Cc: Russell King <linux@....linux.org.uk>
> >> Cc: Tony Luck <tony.luck@...el.com>
> >> Cc: David S. Miller <davem@...emloft.net>
> >> Cc: Ingo Molnar <mingo@...hat.com>
> >> Cc: Guenter Roeck <linux@...ck-us.net>
> >> Cc: Michal Simek <monstr@...str.eu>
> >> Cc: Chris Zankel <chris@...kel.net>
> >> ---
> >> v2->v3:
> >>
> >> - Dropped RFC status
> >> - Removed bridge resources claiming from pci_read_bridge_bases()
> >
> > What do you want me to do with this patch ? I removed the resource
> > claiming - ie the only controversial bit, I can only test on
> > arm64, I would like to make some progress on this otherwise
> > I will have to add the bridge bases read to arm64 pcibios_fixup_bus()
> > and be done with this.
> >
> 
> Lorenzo,
> 
> please give me a few days to test it. I was out on vacation for
> the last two weeks, and I am still struggling to get my test systems
> back to a working state.

No worries, I just wanted to make sure we can make progress on this,
I do not think there is anything controversial in this set, it just
requires testing the mechanical change on all affected archs, that's
the problem.

Thanks a lot for your help !
Lorenzo
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