On Wed, Jan 20, 2016 at 11:13:04AM -0500, Sinan Kaya wrote:
> On 1/20/2016 11:04 AM, Lorenzo Pieralisi wrote:
> > Hi,
> >
> > I noticed that:
> >
> > 79953dd22c1d ("PCI: rcar: Remove dependency on ARM-specific struct hw_pci")
> > cbce7900598c ("PCI: designware: Make driver arch-agnostic")
> >
> > added code in the respective host controller drivers to size bridges
> > and assign resources only if the PCI_PROBE_ONLY flag is clear, which makes
> > me wonder if there exists PCI_PROBE_ONLY set-ups for the respective
> > host controllers:
> >
> > - On ARM PCI_PROBE_ONLY can be set-up only via the command line or
> > by DT (but the host controllers drivers have to check the DT and
> > set it - see of_pci_check_probe_only()
> >
> > in drivers/pci/host/pci-host-generic.c
> >
> > neither designware nor rcar calls that function and I do not see
> > any dts file with that property). Given that I can't see a way
> > to set up PCI_PROBE_ONLY other than the command line on designware
> > or rcar I assume the PCI_PROBE_ONLY set-ups have been tested by
> > forcing it through command line parameter
> >
> > - On ARM64 PCI_PROBE_ONLY can *only* be set via DT, so see above
> >
> > We want to get rid of PCI_PROBE_ONLY on ARM/ARM64:
>
> For platforms that does not have UEFI BIOS, it makes sense to remove
> the probe only option as the firmware is not doing anything.
>
> For server like arm64 platforms, the behavior should be identical to
> x86 world. The UEFI BIOS sets up the resources, kernel uses the
> resources.
>
> Can we set this flag all the time for ACPI builds instead?
>
> What's so special about arm64 that we can't do probe only builds and
> x86 can do?
Ok, let me give you a bit of background otherwise we talk at cross
purposes here.
ARM and ARM64 arch code is currently forced to prevent calling:
pci_enable_resources() (eg arch/arm/kernel/bios32.c)
because, on platforms that are "PCI_PROBE_ONLY" (whatever that means),
resources are neither assigned nor claimed. This works in practice
but it is basically a workaround (ie the resources hierarchy is not
validated at all in the kernel on PCI_PROBE_ONLY systems) and we want
to get rid of that, that's what I mean by "get rid of PCI_PROBE_ONLY".
Now, how we can get rid of that plaster in pcibios_enable_device().
To do that, we must claim resources on PCI_PROBE_ONLY systems, but
I know for certain Bjorn does not like the idea (I let you trawl
the archives - at least he does not accept the idea of claiming
resources ONLY on PCI_PROBE_ONLY systems, he thinks we should
always claim resources regardless of that flag and fall-back to
reassigning them in case claiming fails. That's perfectly reasonable,
at least on systems with FW initializing PCI). The problem is dealing
with legacy, so switching to resources claiming by default is a tad
complicated, at least for testing (code is easy to implement).
So yes, on arm64 ACPI systems, regardless of PCI_PROBE_ONLY, resources
must be claimed and reassigned if claiming fails (as x86), we start from
fresh and we *must* do it from the beginning.
We can do that on arm64 (for ACPI - where PCI FW set-up is _supposed_ to
be correct).
On other arm64 (and arm) platforms, the question is whether it is safe
to claim resources or not. Remember that there are already PCI host
controller drivers in the kernel (with equivalent FW set-up) so there
is legacy.
Resources claiming and assignment should be managed in arch code,
not in host controllers specific code, and that's the reason I
complained in this RFC about the scattering of PCI_PROBE_ONLY flag
checks in host drivers, it is becoming unmanageable (if useful
at all on designware and rcar, I would like to know if there are
PCI_PROBE_ONLY set-ups probing those host drivers).
Does it make the point clearer ?
> > https://patchwork.ozlabs.org/patch/545671/
> >
> > so unless you really have *existing* set-ups that require it, please
> > remove the respective checks from the host controller drivers, this is
> > becoming a serious issue, because either:
> >
> > - we claim resources if and only if PCI_PROBE_ONLY is set
> >
> > Either like this (to be done for every host controllers and ARM
> > bios32):
> >
> > https://patchwork.ozlabs.org/patch/545670/
> >
> > or in core ARM/ARM64 code - eg pcibios_fixup_bus() - (to avoid adding a
> > resource claiming call in ALL PCI host controllers)
> >
> > - or we *always* carry out resource claiming regardless of PCI_PROBE_ONLY
> > (but on ARM we can't really do that since PCI FW set-up on most of the
> > platforms is not present)
> >
> > On PCI_PROBE_ONLY systems resources claiming is mandatory if we want
> > to get rid of arches workarounds:
>
> I'm hoping to see x86 like behavior on ARM64 without any gotchas as
> there is nothing special about CPU type when it comes to PCI.
As I said, we must enforce it with ACPI, for DT platforms I am all
ears to decide how we can implement it sanely (I think the only way
to do it is by claiming the PCI resources on PCI_PROBE_ONLY systems,
that's not ideal but it simplifies things a lot).
Thanks,
Lorenzo
>
> >
> > https://patchwork.ozlabs.org/patch/545671/
> >
> > Comments very appreciated.
> >
> > Thanks,
> > Lorenzo
> > --
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>
>
> --
> Sinan Kaya
> Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
>
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