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SubjectRe: [RFC/RFT PATCH] PCI: move pci_read_bridge_bases to the generic PCI layer
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@arm.com>
> Cc: Ralf Baechle <ralf@linux-mips.org>
> Cc: James E.J. Bottomley <jejb@parisc-linux.org>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Cc: Richard Henderson <rth@twiddle.net>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: David Howells <dhowells@redhat.com>
> Cc: Russell King <linux@arm.linux.org.uk>
> Cc: Tony Luck <tony.luck@intel.com>
> Cc: David S. Miller <davem@davemloft.net>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Michal Simek <monstr@monstr.eu>
> Cc: Koichi Yasutake <yasutake.koichi@jp.panasonic.com>
> Cc: Chris Zankel <chris@zankel.net>
> ---
> 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?

Thanks,
Suravee



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