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

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Date:   Wed, 23 Nov 2016 12:21:03 +0100
From:   Tomasz Nowicki <tn@...ihalf.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
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 Bjorn,

On 23.11.2016 00:13, Bjorn Helgaas wrote:
> 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.
>

Well spotted. I agree, we need to fix this. How about this:
diff --git a/arch/arm64/kernel/pci.c b/arch/arm64/kernel/pci.c
index fb439c7..31c0e1c 100644
--- a/arch/arm64/kernel/pci.c
+++ b/arch/arm64/kernel/pci.c
@@ -152,33 +152,35 @@ static void pci_acpi_generic_release_info(struct 
acpi_pci_root_info *ci)

         ri = container_of(ci, struct acpi_pci_generic_root_info, common);
         pci_ecam_free(ri->cfg);
+       kfree(ci->ops);
         kfree(ri);
  }

-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)
  {
         int node = acpi_get_node(root->device->handle);
         struct acpi_pci_generic_root_info *ri;
         struct pci_bus *bus, *child;
+       struct acpi_pci_root_ops *root_ops;

         ri = kzalloc_node(sizeof(*ri), GFP_KERNEL, node);
         if (!ri)
                 return NULL;

+       root_ops = kzalloc_node(sizeof(*root_ops), GFP_KERNEL, node);
+       if (!root_ops)
+               return NULL;
+
         ri->cfg = pci_acpi_setup_ecam_mapping(root);
         if (!ri->cfg) {
                 kfree(ri);
+               kfree(root_ops);
                 return NULL;
         }

-       acpi_pci_root_ops.pci_ops = &ri->cfg->ops->pci_ops;
-       bus = acpi_pci_root_create(root, &acpi_pci_root_ops, &ri->common,
-                                  ri->cfg);
+       root_ops->release_info = pci_acpi_generic_release_info;
+       root_ops->pci_ops = &ri->cfg->ops->pci_ops;
+       bus = acpi_pci_root_create(root, root_ops, &ri->common, ri->cfg);
         if (!bus)
                 return NULL;

Of course, this should be the part of ECAM quirks core patches.

The other option we have is to remove "struct pci_ops *pci_ops;" from 
acpi_pci_root_ops structure and pass struct pci_ops as an extra argument 
to acpi_pci_root_create(). What do you think?

Thanks,
Tomasz