[U-Boot] [PATCH] pci: Support parsing PCI controller DT subnodes

[Marek Vasut <marek.vasut@gmail.com>]

On 08/09/2018 01:24 AM, Bin Meng wrote:
> Hi Marek,
> 
> On Thu, Aug 9, 2018 at 3:37 AM, Marek Vasut <marek.vasut@gmail.com> wrote:
>> On 08/08/2018 05:32 PM, Bin Meng wrote:
>>> Hi Marek,
>>>
>>> On Wed, Aug 8, 2018 at 10:33 PM, Marek Vasut <marek.vasut@gmail.com> wrote:
>>>> On 08/08/2018 03:39 PM, Bin Meng wrote:
>>>>> Hi Marek,
>>>>>
>>>>> On Wed, Aug 8, 2018 at 9:24 PM, Marek Vasut <marek.vasut@gmail.com> wrote:
>>>>>> On 08/08/2018 03:14 PM, Bin Meng wrote:
>>>>>>> Hi Marek,
>>>>>>>
>>>>>>> On Wed, Aug 8, 2018 at 9:03 PM, Marek Vasut <marek.vasut@gmail.com> wrote:
>>>>>>>> The PCI controller can have DT subnodes describing extra properties
>>>>>>>> of particular PCI devices, ie. a PHY attached to an EHCI controller
>>>>>>>> on a PCI bus. This patch parses those DT subnodes and assigns a node
>>>>>>>> to the PCI device instance, so that the driver can extract details
>>>>>>>> from that node and ie. configure the PHY using the PHY subsystem.
>>>>>>>>
>>>>>>>> Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
>>>>>>>> Cc: Simon Glass <sjg@chromium.org>
>>>>>>>> ---
>>>>>>>>  drivers/pci/pci-uclass.c | 14 ++++++++++++++
>>>>>>>>  1 file changed, 14 insertions(+)
>>>>>>>>
>>>>>>>> diff --git a/drivers/pci/pci-uclass.c b/drivers/pci/pci-uclass.c
>>>>>>>> index 46e9c71bdf..306bea0dbf 100644
>>>>>>>> --- a/drivers/pci/pci-uclass.c
>>>>>>>> +++ b/drivers/pci/pci-uclass.c
>>>>>>>> @@ -662,6 +662,8 @@ static int pci_find_and_bind_driver(struct udevice *parent,
>>>>>>>>                 for (id = entry->match;
>>>>>>>>                      id->vendor || id->subvendor || id->class_mask;
>>>>>>>>                      id++) {
>>>>>>>> +                       ofnode node;
>>>>>>>> +
>>>>>>>>                         if (!pci_match_one_id(id, find_id))
>>>>>>>>                                 continue;
>>>>>>>>
>>>>>>>> @@ -691,6 +693,18 @@ static int pci_find_and_bind_driver(struct udevice *parent,
>>>>>>>>                                 goto error;
>>>>>>>>                         debug("%s: Match found: %s\n", __func__, drv->name);
>>>>>>>>                         dev->driver_data = find_id->driver_data;
>>>>>>>> +
>>>>>>>> +                       dev_for_each_subnode(node, parent) {
>>>>>>>> +                               phys_addr_t df, size;
>>>>>>>> +                               df = ofnode_get_addr_size(node, "reg", &size);
>>>>>>>> +
>>>>>>>> +                               if (PCI_FUNC(df) == PCI_FUNC(bdf) &&
>>>>>>>> +                                   PCI_DEV(df) == PCI_DEV(bdf)) {
>>>>>>>> +                                       dev->node = node;
>>>>>>>> +                                       break;
>>>>>>>> +                               }
>>>>>>>
>>>>>>> The function pci_find_and_bind_driver() is supposed to bind devices
>>>>>>> that are NOT in the device tree. Adding device tree access in this
>>>>>>> routine is quite odd. You can add the EHCI controller that need such
>>>>>>> PHY subnodes in the device tree and there is no need to modify
>>>>>>> anything I believe. If you are looking for an example, please check
>>>>>>> pciuart0 in arch/x86/dts/crownbay.dts.
>>>>>>
>>>>>> Well this does not work for me, the EHCI PCI doesn't get a DT node
>>>>>> assigned, check r8a7794.dtsi for the PCI devices I use.
>>>>>>
>>>>>
>>>>> I think that's because you don't specify a "compatible" string for
>>>>> these two EHCI PCI nodes.
>>>>
>>>> That's perfectly fine, why should I specify it ? Linux has no problem
>>>> with it either.
>>>>
>>>
>>> Without a "compatible" string, DM does not bind any device in the
>>> device tree to a driver, hence no device node created. This is not
>>> Linux.
>>
>> DT is NOT Linux specific, it is OS-agnostic, DT describes hardware and
>> hardware only. If U-Boot cannot parse DT correctly, U-Boot is broken and
>> must be fixed.
>>
>> This is a fix. If there is a better fix, I am open to it.
>>
> 
> Sorry this is a hack to current U-Boot implementation, not fix.

I am waiting for a better solution or suggestion ...

> The fix should be adding "ehci-pci" compatible string in the r8a7794.dtsi.

Wrong. The DT is perfectly valid as is.

The device sitting at a particular slot/function can very well be ie.
xhci controller and the DT node would be valid for it too, unless you
enforce a compatible, which will mess things up.

Each PCI device already has a PCI ID and class which is used to identify
it and based on which the drivers bind to it, so a DT compatible is NOT
needed and is actually redundant and harmful.

What is needed here is to assign a valid DT node to a driver instance of
a PCI device if such a matching node exists in DT and that is all this
patch does.

> I disagree DT is OS-agnostic. This are lots of stuff in DT that are
> OS-specific. eg: there are lots of bindings in DT that requires
> Linux's device driver framework to work with.

This logic is flawed. If there exists a binding which depends on some
behavior of specific OS then the binding is likely wrong. That
specifically does not imply DT is OS-specific. Again, it is not and that
is by design. The DT must be usable by multiple OSes with very different
internal design, Solaris, *BSD, Linux, U-Boot to name a few.

> As you said, DT is just
> a standard to describe hardware and hardware only. But there are
> various methods to describe hardware in DT that's why we have a proper
> defined bindings in Linux.

defined bindings, yes. In Linux ... no ... the HW is OS-independent, so
is it's description in DT.

> How OS parses and utilizes these
> information is completely on their own.
> 
> Regards,
> Bin
> 


-- 
Best regards,
Marek Vasut