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

[Suravee Suthikulanit]

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?

Thanks,
Suravee

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