linux-kernel - Re: [PATCH v3] PCI/ACPI: xgene: Add ECAM quirk for X-Gene PCIe controller

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Date:   Thu, 1 Dec 2016 14:26:29 -0500
From:   Jon Masters <jcm@...hat.com>
To:     Mark Salter <msalter@...hat.com>,
        Bjorn Helgaas <helgaas@...nel.org>, Duc Dang <dhdang@....com>
Cc:     Rafael Wysocki <rafael@...nel.org>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
        Arnd Bergmann <arnd@...db.de>, linux-pci@...r.kernel.org,
        linux-arm <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Tomasz Nowicki <tn@...ihalf.com>, patches <patches@....com>
Subject: Re: [PATCH v3] PCI/ACPI: xgene: Add ECAM quirk for X-Gene PCIe
 controller

On 12/01/2016 02:20 PM, Mark Salter wrote:
> On Thu, 2016-12-01 at 12:33 -0600, Bjorn Helgaas wrote:

>>> +	csr = &xgene_v1_csr_res[root->segment];
>> This makes me nervous because root->segment comes from the ACPI _SEG,
>> and if firmware gives us junk in _SEG, we will reference something in
>> the weeds.
> 
> The SoC provide some number of RC bridges, each with a different base
> for some mmio registers. Even if segment is legitimate in MCFG, there
> is still a problem if a platform doesn't use the segment ordering
> implied by the code. But the PNP0A03 _CRS does have this base address
> as the first memory resource, so we could get it from there and not
> have hard-coded addresses and implied ording in the quirk code.
> 
> I have tested a modified version of these quirks using this to
> get the CSR base and it works on the 3 different platforms I have
> access to.
> 
> static int xgene_pcie_get_csr(struct device *dev, struct resource *r)
> {
> 	struct acpi_device *adev = to_acpi_device(dev);
> 	unsigned long flags;
> 	struct list_head list;
> 	struct resource_entry *entry;
> 	int ret;
> 
> 	INIT_LIST_HEAD(&list);
> 	flags = IORESOURCE_MEM;
> 	ret = acpi_dev_get_resources(adev, &list,
> 				     acpi_dev_filter_resource_type_cb,
> 				     (void *)flags);
> 	if (ret < 0) {
> 		dev_err(dev, "failed to parse _CRS, error: %d\n", ret);
> 		return ret;
> 	} else if (ret == 0) {
> 		dev_err(dev, "no memory resources present in _CRS\n");
> 		return -EINVAL;
> 	}
> 
> 	entry = list_first_entry(&list, struct resource_entry, node);
> 	*r = *entry->res;
> 	acpi_dev_free_resource_list(&list);
> 	return 0;
> }

This seems a lot safer. At some point trusting firmware to provide the
correct _CRS for the RC in use is better than hard coding for every
possible implementation configuration of an X-Gene SoC.

Jon.

-- 
Computer Architect | Sent from my Fedora powered laptop