linux-kernel - Re: [PATCH V9 11/11] ARM64/PCI: Support for ACPI based PCI host controller

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Date:   Tue, 22 Nov 2016 17:13:21 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Tomasz Nowicki <tn@...ihalf.com>
Cc:     arnd@...db.de, will.deacon@....com, catalin.marinas@....com,
        rafael@...nel.org, hanjun.guo@...aro.org,
        Lorenzo.Pieralisi@....com, okaya@...eaurora.org,
        jchandra@...adcom.com, robert.richter@...iumnetworks.com,
        mw@...ihalf.com, Liviu.Dudau@....com, ddaney@...iumnetworks.com,
        wangyijing@...wei.com, Suravee.Suthikulpanit@....com,
        msalter@...hat.com, linux-pci@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org, linaro-acpi@...ts.linaro.org,
        jcm@...hat.com, andrea.gallo@...aro.org, dhdang@....com,
        jeremy.linton@....com, liudongdong3@...wei.com, cov@...eaurora.org
Subject: Re: [PATCH V9 11/11] ARM64/PCI: Support for ACPI based PCI host
 controller

Hi Tomasz,

On Fri, Jun 10, 2016 at 09:55:19PM +0200, Tomasz Nowicki wrote:
> Implement pci_acpi_scan_root and other arch-specific call so that ARM64
> can start using ACPI to setup and enumerate PCI buses.
> 
> Prior to buses enumeration the pci_acpi_scan_root() implementation looks
> for configuration space start address (obtained through ACPI _CBA method or
> MCFG interface). If succeed, it uses ECAM library to create new mapping.
> Then it attaches generic ECAM ops (pci_generic_ecam_ops) which are used
> for accessing configuration space later on.
> ...

> +static struct acpi_pci_root_ops acpi_pci_root_ops = {
> +	.release_info = pci_acpi_generic_release_info,
> +};
> +
> +/* Interface called from ACPI code to setup PCI host controller */
>  struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root)
>  {
> -	/* TODO: Should be revisited when implementing PCI on ACPI */
> -	return NULL;
> +	int node = acpi_get_node(root->device->handle);
> +	struct acpi_pci_generic_root_info *ri;
> +	struct pci_bus *bus, *child;
> +
> +	ri = kzalloc_node(sizeof(*ri), GFP_KERNEL, node);
> +	if (!ri)
> +		return NULL;
> +
> +	ri->cfg = pci_acpi_setup_ecam_mapping(root);
> +	if (!ri->cfg) {
> +		kfree(ri);
> +		return NULL;
> +	}
> +
> +	acpi_pci_root_ops.pci_ops = &ri->cfg->ops->pci_ops;

This has already been merged, but this isn't right, is it?  We're
writing a host controller-specific pointer into the single system-wide
acpi_pci_root_ops, then passing it on to acpi_pci_root_create().

Today, I think ri->cfg->ops->pci_ops is always &pci_generic_ecam_ops,
from this path:

  ri->cfg = pci_acpi_setup_ecam_mapping
    cfg = pci_ecam_create(..., &pci_generic_ecam_ops)
      cfg = kzalloc(...)
      cfg->ops = ops             # &pci_generic_ecam_ops

But we're about to merge the ECAM quirks series, which will mean it
may not be &pci_generic_ecam_ops.  Even apart from the ECAM quirks, we
should avoid this pattern of putting device-specific info in a single
shared structure because it's too difficult to verify that it's
correct.

> +	bus = acpi_pci_root_create(root, &acpi_pci_root_ops, &ri->common,
> +				   ri->cfg);

Bjorn