Re: [RFC/RFT PATCH] PCI: move pci_read_bridge_bases to the generic PCI layer

[Lorenzo Pieralisi]

On Wed, May 27, 2015 at 05:42:52PM +0100, Suravee Suthikulanit wrote:
> Hi Lorenzo,
> 
> Sorry for late reply.
> 
> On 5/21/2015 8:14 AM, 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@xxxxxxx>
> > Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
> > Cc: James E.J. Bottomley <jejb@xxxxxxxxxxxxxxxx>
> > Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> > Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> > Cc: Richard Henderson <rth@xxxxxxxxxxx>
> > Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> > Cc: David Howells <dhowells@xxxxxxxxxx>
> > Cc: Russell King <linux@xxxxxxxxxxxxxxxx>
> > Cc: Tony Luck <tony.luck@xxxxxxxxx>
> > Cc: David S. Miller <davem@xxxxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: Michal Simek <monstr@xxxxxxxxx>
> > Cc: Koichi Yasutake <yasutake.koichi@xxxxxxxxxxxxxxxx>
> > Cc: Chris Zankel <chris@xxxxxxxxxx>
> > ---
> >   arch/alpha/kernel/pci.c          |  7 +------
> >   arch/frv/mb93090-mb00/pci-vdk.c  |  2 --
> >   arch/ia64/pci/pci.c              |  1 -
> >   arch/microblaze/pci/pci-common.c |  9 +--------
> >   arch/mips/pci/pci.c              |  6 ------
> >   arch/mn10300/unit-asb2305/pci.c  |  1 -
> >   arch/powerpc/kernel/pci-common.c |  8 +-------
> >   arch/x86/pci/common.c            |  1 -
> >   arch/xtensa/kernel/pci.c         |  4 ----
> >   drivers/parisc/dino.c            |  3 ---
> >   drivers/parisc/lba_pci.c         |  1 -
> >   drivers/pci/probe.c              | 11 ++++++++++-
> >   12 files changed, 13 insertions(+), 41 deletions(-)
> >
> > [.....]
>  >
> > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> > index 062fee6..335d9f2 100644
> > --- a/drivers/pci/probe.c
> > +++ b/drivers/pci/probe.c
> > @@ -453,7 +453,11 @@ void pci_read_bridge_bases(struct pci_bus *child)
> >   	struct resource *res;
> >   	int i;
> >
> > -	if (pci_is_root_bus(child))	/* It's a host bus, nothing to read */
> > +	/*
> > +	 * If it is not a PCI bridge there is nothing to read
> > +	 */
> > +	if (pci_is_root_bus(child) || !dev ||
> > +		!((dev->class >> 8) == PCI_CLASS_BRIDGE_PCI))
> >   		return;
> >
> >   	dev_info(&dev->dev, "PCI bridge to %pR%s\n",
> > @@ -1878,6 +1882,11 @@ unsigned int pci_scan_child_bus(struct pci_bus *bus)
> >   	 * all PCI-to-PCI bridges on this bus.
> >   	 */
> >   	if (!bus->is_added) {
> > +		/*
> > +		 * Read and initialize bridge resources.
> > +		 */
> > +		pci_read_bridge_bases(bus);
> > +
> >   		dev_dbg(&bus->dev, "fixups for bus\n");
> >   		pcibios_fixup_bus(bus);
> >   		bus->is_added = 1;
> >
> 
> So, I have tested the patch on ARM64 system w/ PROBE_ONLY mode, and 
> noticed that we are calling pci_read_bridge_bases() after adding the 
> devices on the slots. This is not soon enough since the downstream 
> devices still failing to claim resources.
> 
> However, do you think we can move pci_read_bridge_bases() before the 
> pci_scan_slot() loop?

Right, how about moving it to pci_scan_bridge() before calling the
respective pci_scan_child_bus() ? I think it belongs there anyway.

Thanks,
Lorenzo
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