Re: [RFC PATCH v3 2/2] ARM64/PCI: Start using quirks handling for ACPI based PCI host controller

[Lorenzo Pieralisi]

On Mon, Jun 20, 2016 at 12:12:24PM -0700, Duc Dang wrote:
> On Mon, Jun 20, 2016 at 10:17 AM, Christopher Covington
> <cov@xxxxxxxxxxxxxx> wrote:
> > Hi Duc,
> >
> > On 06/20/2016 05:42 AM, Lorenzo Pieralisi wrote:
> >> On Fri, Jun 17, 2016 at 02:37:02PM -0700, Duc Dang wrote:
> >>> On Thu, Jun 16, 2016 at 10:48 AM, Lorenzo Pieralisi
> >>> <lorenzo.pieralisi@xxxxxxx> wrote:
> >>>> On Wed, Jun 15, 2016 at 11:34:11AM -0400, Christopher Covington wrote:
> >>>>> From: Tomasz Nowicki <tn@xxxxxxxxxxxx>
> >>>>>
> >>>>> pci_generic_ecam_ops is used by default. Since there are platforms
> >>>>> which have non-compliant ECAM space we need to overwrite these
> >>>>> accessors prior to PCI buses enumeration. In order to do that
> >>>>> we call pci_mcfg_get_ops to retrieve pci_ecam_ops structure so that
> >>>>> we can use proper PCI config space accessors and bus_shift.
> >>>>>
> >>>>> pci_generic_ecam_ops is still used for platforms free from quirks.
> >>>>>
> >>>>> Signed-off-by: Tomasz Nowicki <tn@xxxxxxxxxxxx>
> >>>>> ---
> >>>>>  arch/arm64/kernel/pci.c | 7 ++++---
> >>>>>  1 file changed, 4 insertions(+), 3 deletions(-)
> >>>>>
> >>>>> diff --git a/arch/arm64/kernel/pci.c b/arch/arm64/kernel/pci.c
> >>>>> index 94cd43c..a891bda 100644
> >>>>> --- a/arch/arm64/kernel/pci.c
> >>>>> +++ b/arch/arm64/kernel/pci.c
> >>>>> @@ -139,6 +139,7 @@ pci_acpi_setup_ecam_mapping(struct acpi_pci_root *root)
> >>>>>       struct pci_config_window *cfg;
> >>>>>       struct resource cfgres;
> >>>>>       unsigned int bsz;
> >>>>> +     struct pci_ecam_ops *ops;
> >>>>>
> >>>>>       /* Use address from _CBA if present, otherwise lookup MCFG */
> >>>>>       if (!root->mcfg_addr)
> >>>>> @@ -150,12 +151,12 @@ pci_acpi_setup_ecam_mapping(struct acpi_pci_root *root)
> >>>>>               return NULL;
> >>>>>       }
> >>>>>
> >>>>> -     bsz = 1 << pci_generic_ecam_ops.bus_shift;
> >>>>> +     ops = pci_mcfg_get_ops(root);
> >>>>> +     bsz = 1 << ops->bus_shift;
> >>>>>       cfgres.start = root->mcfg_addr + bus_res->start * bsz;
> >>>>>       cfgres.end = cfgres.start + resource_size(bus_res) * bsz - 1;
> >>>>>       cfgres.flags = IORESOURCE_MEM;
> >>>>> -     cfg = pci_ecam_create(&root->device->dev, &cfgres, bus_res,
> >>>>> -                           &pci_generic_ecam_ops);
> >>>>> +     cfg = pci_ecam_create(&root->device->dev, &cfgres, bus_res, ops);
> >>>>
> >>>> Arnd pointed this out already, I think that's the only pending question
> >>>> here.
> >>>>
> >>>> pci_ecam_create() maps ECAM space for config regions retrieved from
> >>>> the MCFG, which are *supposed* to be ECAM compliant.
> >>>>
> >>>> Do we think that's *always* correct/safe regardless of the kind
> >>>> of quirk we are currently fixing up ?
> >>>>
> >>>> Or we do think that configuration space regions should come from
> >>>> a different resource declared in the ACPI namespace if the regions
> >>>> are not MCFG/ECAM compliant (ie config space is not defined through
> >>>> MCFG at all - possibly through a _CRS method for a vendor specific
> >>>> _HID under the PNP0A03 node ?)
> >>>
> >>> Hi Lorenzo,
> >>>
> >>> For X-Gene: the ECAM space is used to access the configuration space
> >>> of PCIe devices, with additional help from controller register to
> >>> specify the bus, device and function number. Below is the RFC patch
> >>> that implements ECAM fixup for X-Gene PCIe controller on top of this
> >>> RFC ECAM quirk v3 for your and others reference.
> >>
> >> Yes, you have an additional resource in the PNP0A03 _CRS to describe
> >> your register that is a deliberate abuse of the ACPI standard in
> >> that the _CRS is meant to describe resources that are passed on
> >> to secondary buses
> >
> > A potential alternative came up in an off-list discussion: Would it be
> > better to hard code the information in the quirk workaround than look it
> > up from a repurposed ACPI resource?
> 
> Hi Chris, Lorenzo,
> 
> Thanks for looking into this.
> 
> Yes, I am open for this approach and I think it may work. I can +
> check the pci_config_window resource start address (cfg->res.start) to
> figure out the controller and then get the fixed controller register
> address or + using the domain number to identify the controller.

First thing to do is to remove config space entry from PNP0A03
_CRS, that's a FW bug.

You could use the {bus-range, domain} to get that register address,
anyway, that's not the main concern here.

Thanks,
Lorenzo

> Regards,
> Duc Dang.
> >
> > Supporting quirk workarounds for early, non-compliant hardware is
> > helpful and perhaps necessary for bootstrapping the ecosystem in a
> > timely manner. But we don't really want to provide an expandable or
> > reusable interface that would make it easy for new hardware to remain
> > non-compliant.
> >
> > Regards,
> > Cov
> >
> > --
> > Qualcomm Innovation Center, Inc.
> > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
> > a Linux Foundation Collaborative Project
>