Re: [PATCH] of: treat PCI config space as IORESOURCE_MEM type

[Liviu Dudau]

On Fri, May 30, 2014 at 03:45:05PM -0500, Kumar Gala wrote:
> 
> On May 29, 2014, at 8:41 PM, Liviu Dudau <liviu@xxxxxxxxxxx> wrote:
> 
> > On Thu, May 29, 2014 at 07:29:31PM -0600, Bjorn Helgaas wrote:
> >> On Thu, May 29, 2014 at 6:56 PM, Liviu Dudau <liviu@xxxxxxxxxxx> wrote:
> >>> On Thu, May 29, 2014 at 03:51:28PM -0500, Kumar Gala wrote:
> >>>> 
> >>>> On May 29, 2014, at 3:44 PM, Rob Herring <robherring2@xxxxxxxxx> wrote:
> >>>> 
> >>>>> On Thu, May 29, 2014 at 11:03 AM, Kumar Gala <galak@xxxxxxxxxxxxxx> wrote:
> >>>>>> If we have a PCI config space specified in something like a ranges
> >>>>>> property we should treat it as memory type resource.
> >>>>> 
> >>>>> Config space should not be in ranges[1]. We have some cases that are,
> >>>>> but we don't want new ones.
> >>>> 
> >>>> For the cases we have I agree, however an ECAM based cfg seems completely legit.
> >>>> 
> >>>>>> Signed-off-by: Kumar Gala <galak@xxxxxxxxxxxxxx>
> >>>>>> ---
> >>>>>> drivers/of/address.c | 3 +++
> >>>>>> 1 file changed, 3 insertions(+)
> >>>>>> 
> >>>>>> diff --git a/drivers/of/address.c b/drivers/of/address.c
> >>>>>> index cb4242a..4e7ee59 100644
> >>>>>> --- a/drivers/of/address.c
> >>>>>> +++ b/drivers/of/address.c
> >>>>>> @@ -122,6 +122,9 @@ static unsigned int of_bus_pci_get_flags(const __be32 *addr)
> >>>>>>       u32 w = be32_to_cpup(addr);
> >>>>>> 
> >>>>>>       switch((w >> 24) & 0x03) {
> >>>>>> +       case 0x00: /* cfg space */
> >>>>>> +               flags |= IORESOURCE_MEM;
> >>>>>> +               break;
> >>>>> 
> >>>>> How would you then distinguish actual memory ranges?
> >>>> 
> >>>> One assumes you are still looking at pci_space as part of of_pci_range
> >>> 
> >>> That doesn't happen when you start scanning the bus. The existing code will
> >>> use the IORESOURCE_MEM for allocating memory space for devices, which is
> >>> not what you want. Did you test your patch on any PCI system? I'm pretty
> >>> sure that with my patch series that tries to make a generic framework for
> >>> host controllers this will fail.
> >>> 
> >>> We really need a IORESOURCE_CFG flag for this space.
> >> 
> >> Maybe, but I'm not convinced yet.  The existing IORESOURCE_TYPE_BITS
> >> types are for things that are mutually exclusive address spaces.  I
> >> think this discussion is about ECAM, where the CPU side is definitely
> >> in the same address space (IORESOURCE_MEM) as RAM, APICs, host bridge
> >> apertures, device MMIO, etc.  The ECAM area must appear in the
> >> iomem_resource tree so we avoid it when allocating other areas.
> > 
> > Agree, I'm only concerned that if this ECAM config space gets added to
> > the list of pci_host_bridge windows it will be indistinguishable from
> > IORESOURCE_MEM resources and pci_create_root_bus() will add it to the
> > bus and allow devices present on that bus to be assigned addresses from
> > that range. Which might not be what one wants for certain BARs.
> > 
> > I've had an aborted attempt to parse ECAM ranges in one version of my
> > series (granted, I was trying to hack the IORESOURCE_TYPE_BITS as well)
> > and things got horribly wrong quickly. I could give this patch a go with
> > my series tomorrow when I'm in the office and report back.
> 
> We need to fix the parsing code to be smarter about this case.

Wow, what a sweeping statement! Did you not understand that the issue is not
the parsing code but the way the rest of the core code uses an IORESOURCE_MEM
once you have parsed it into a resource structure and added it to the list
of pci_host_bridge_windows?

Best regards,
Liviu

> 
> - k
> -- 
> Employee of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation
> 
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