[PATCH 11/11] RFC: ARM: get PCI device IRQs from device tree

[PATCH 11/11] RFC: ARM: get PCI device IRQs from device tree

[Arnd Bergmann]

On Thursday 04 April 2013, Linus Walleij wrote:
> This adds the interrupt-map property to the PCIv3 DTS file
> and makes the bridge obtain mappings from the device tree.
> 
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> ---
> This currently bugs out - when trying to get the IRQs for
> devices of_irq_map_pci() reads the IRQ pin from the PCI config
> space successfully, then comes to trying to look up the parent
> PCI device by checking pdev->bus->self, which is NULL, then
> tries to treat it as a bridge doing pci_bus_to_OF_node(pdev->bus)
> which also results in NULL and it bails out.
> 
> No clue why this is so - some problem with the parent of this
> bus not being a PCI device in itself? Help.

All the PowerPC implementations I remember had the PCI bus
as a device under the root node. It's very possible that it's
just a bug in of_irq_map_pci().

	Arnd

[PATCH 00/11] ARM: integrator PCI DT adaption

[Arnd Bergmann]

On Thursday 04 April 2013, Linus Walleij wrote:
> This patch series converts the Integrator/AP v3 PCI adapter
> to use device tree, up until the point where I try to set
> up the IRQ map and fail. Help on how to get the last patch
> working is appreciated.
> 
> This series is dependent on the first three patches for OF
> recently submitted by Thomas Petazzoni, I will not be able
> to submit them until that stuff is merged somewhere (like
> ARM SoC).

Looks very nice!

Acked-by: Arnd Bergmann <arnd@arndb.de>

including the last [RFC] patch, which also looks right to me,
even though you tell me it doesn't work ;-)

[PATCH 11/11] RFC: ARM: get PCI device IRQs from device tree

[Linus Walleij]

On Thu, Apr 4, 2013 at 5:27 PM, Arnd Bergmann <arnd@arndb.de> wrote:
> On Thursday 04 April 2013, Linus Walleij wrote:
>> This adds the interrupt-map property to the PCIv3 DTS file
>> and makes the bridge obtain mappings from the device tree.
>>
>> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
>> ---
>> This currently bugs out - when trying to get the IRQs for
>> devices of_irq_map_pci() reads the IRQ pin from the PCI config
>> space successfully, then comes to trying to look up the parent
>> PCI device by checking pdev->bus->self, which is NULL, then
>> tries to treat it as a bridge doing pci_bus_to_OF_node(pdev->bus)
>> which also results in NULL and it bails out.
>>
>> No clue why this is so - some problem with the parent of this
>> bus not being a PCI device in itself? Help.
>
> All the PowerPC implementations I remember had the PCI bus
> as a device under the root node. It's very possible that it's
> just a bug in of_irq_map_pci().

Hm, quite hard to figure this one out.

Benjamin, any hints?

Yours,
Linus Walleij

[PATCH 11/11] RFC: ARM: get PCI device IRQs from device tree

[Linus Walleij]

On Thu, Apr 4, 2013 at 5:01 PM, Linus Walleij <linus.walleij@linaro.org> wrote:

> This currently bugs out - when trying to get the IRQs for
> devices of_irq_map_pci() reads the IRQ pin from the PCI config
> space successfully, then comes to trying to look up the parent
> PCI device by checking pdev->bus->self, which is NULL, then
> tries to treat it as a bridge doing pci_bus_to_OF_node(pdev->bus)
> which also results in NULL and it bails out.
>
> No clue why this is so - some problem with the parent of this
> bus not being a PCI device in itself? Help.

Tracked this down to a point where in drivers/pci/of.c
pci_set_bus_of_node() is called on the root bus, at which
point it calls pcibios_get_phb_of_node() which has no clue
on how to obtain the DT node for the root hub. (Only bridges.)

Inserting this na?ve fragment into the PCI driver makes things
tick:

+struct device_node *static_root;
+
+struct device_node *pcibios_get_phb_of_node(struct pci_bus *bus)
+{
+       return static_root;
+}
+

In probe():
+       static_root = np;

It'll override the weak symbol and make things work.

I guess this is something for kernel/bios32.c to implement
if we want to support DT on these PCI adapters, so looking
into that next...

But how do others get their things to work? Not using bios32?
I wonder...

Yours,
Linus Walleij

[PATCH 11/11] RFC: ARM: get PCI device IRQs from device tree

[Andrew Murray]

On Thu, Apr 11, 2013 at 09:27:53PM +0100, Linus Walleij wrote:
> On Thu, Apr 4, 2013 at 5:01 PM, Linus Walleij <linus.walleij@linaro.org> wrote:
> 
> > This currently bugs out - when trying to get the IRQs for
> > devices of_irq_map_pci() reads the IRQ pin from the PCI config
> > space successfully, then comes to trying to look up the parent
> > PCI device by checking pdev->bus->self, which is NULL, then
> > tries to treat it as a bridge doing pci_bus_to_OF_node(pdev->bus)
> > which also results in NULL and it bails out.
> >
> > No clue why this is so - some problem with the parent of this
> > bus not being a PCI device in itself? Help.
> 
> Tracked this down to a point where in drivers/pci/of.c
> pci_set_bus_of_node() is called on the root bus, at which
> point it calls pcibios_get_phb_of_node() which has no clue
> on how to obtain the DT node for the root hub. (Only bridges.)
> 
> Inserting this na?ve fragment into the PCI driver makes things
> tick:
> 
> +struct device_node *static_root;
> +
> +struct device_node *pcibios_get_phb_of_node(struct pci_bus *bus)
> +{
> +       return static_root;
> +}
> +
> 
> In probe():
> +       static_root = np;
> 
> It'll override the weak symbol and make things work.
> 
> I guess this is something for kernel/bios32.c to implement
> if we want to support DT on these PCI adapters, so looking
> into that next...
> 
> But how do others get their things to work? Not using bios32?
> I wonder...

I think there are a mix of solutions out here, let me try and remember...

* I originally [1] implemented a pcibios_get_phb_of_node function
  in arch/arm/bios32.c this used a new .of_node field from sysdata.
  The idea being that pcibios_init_hw populates .of_node from a field
  of the same name provided by the driver in hw_pci.

* I believe Thierry's approach was to reuse the existing pcibios_get_phb_of_node
  function [2], to do this some changes were needed elsewhere I'm not sure the
  full details of this, I never got around to testing it. But I understand it's
  an approach that Thomas also used. It believe it requries a custom
  implementation of hw->scan such that instead of using pcibios_init_hw's default
  implementation of pci_scan_root_bus (which passes a NULL) your custom
  implementation calls pci_create_root_bus instead and passes a suitable struct
  device.

* I recall having some issues with weak symbols when playing around with
  pcibios_get_phb_of_node - there seems to be some changes in this area [3].

I don't think any of these solutions are ideal - perhaps pcibios_init_hw needs
to be changed... there are patches around which involve passing additional
private data in sys_data/hw_pci see [1] and [4] if this additional data
contains struct device or struct device_node then perhaps they can be plumbed
into the default call to pci_scan_root_bus in bios32? If every ARM DT host
bridge driver needs to implement their own scan function then something isn't
quite right.

I hope that helps.

Andrew Murray

[1] http://patchwork.ozlabs.org/patch/213570
[2] http://www.spinics.net/lists/linux-pci/msg19917.html
[3] http://patchwork1.kernel.org/patch/2394451
[4] http://patchwork.kernel.org/patch/2129431

[PATCH 11/11] RFC: ARM: get PCI device IRQs from device tree

[Linus Walleij]

On Fri, Apr 12, 2013 at 10:22 AM, Andrew Murray <andrew.murray@arm.com> wrote:

Thanks for your prompt reply Andrew!

> I don't think any of these solutions are ideal - perhaps pcibios_init_hw needs
> to be changed... there are patches around which involve passing additional
> private data in sys_data/hw_pci see [1] and [4] if this additional data
> contains struct device or struct device_node then perhaps they can be plumbed
> into the default call to pci_scan_root_bus in bios32? If every ARM DT host
> bridge driver needs to implement their own scan function then something isn't
> quite right.

So yesterday I came up with the scheme of augmenting the
pci_common_init() call in bios32.c to take an additional struct device *parent
argument, then pass that to the pci_create_root_bus() call, as it is hard-coded
to NULL in bios32.c today. Current users were patched to pass NULL
as parent.

When you assign that from a struct device* instatiated from the device tree the
node gets properly resolved and the mappings start to work.

However I might have been too sleepy last night and misfired the patch since
it seems it has not yet made it onto the mailing list ... will resend.

Yours,
Linus Walleij