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

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

On 08/09/2018 04:37 AM, Bin Meng wrote:
> Hi Marek,
> 
> On Thu, Aug 9, 2018 at 8:36 AM, Marek Vasut <marek.vasut@gmail.com> wrote:
>> 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.
>>
> 
> I did not say r8a7794.dtsi is invalid. Being valid does not mean it
> works everywhere. Being valid only means its syntax follows the DTS
> language and does not cause any build error. Adding a "compatible"
> string to a DT node is also perfectly valid. See "Binding Guidelines"
> in devicetree-specification-v0.2.pdf [1]

Hacking up DT to work around bugs in an OS implementation makes it OS
specific and this is incorrect. It is the OS that should be fixed, in
this case U-Boot.

Keep in mind that the DT may even be stored in ROM and can not be modified.

> 4.1 Binding Guidelines
> 4.1.1 General Principles
> When creating a new devicetree representation for a device, a binding
> should be created that fully describes the required properties and
> value of the device. This set of properties shall be sufficiently
> descriptive to provide device drivers with needed attributes of the
> device. Some recommended practices include:
> 1. Define a *compatible* string using the conventions described in section 2.3.1
> ...

Yes, "recommended" . The compatible string is not a hard requirement.

>> 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.
>>
> 
> No, it's not redundant but complementary to existing PCI enumeration
> (vendor/device/class/subclass...) mechanism. Please check "PCI Bus
> Binding" specification [2] which defines how we should describe a PCI
> device using "compatible" string.
> 
> "compatible" Construct a list of names in most-specific to
> least-specific order. The names shall be derived from values of the
> Vendor ID, Device ID, Subsystem Vendor ID, Subsystem ID, Revision ID
> and Class Code bytes, and shall have the following form, and be placed
> in the list in the following order:
> pciVVVV,DDDD.SSSS.ssss.RR
> pciVVVV,DDDD.SSSS.ssss
> pciSSSS,ssss
> pciVVVV,DDDD.RR
> pciVVVV,DDDD
> pciclass,CCSSPP
> pciclass,CCSS
> ...

Where does it say that the "compatible" string is mandatory ? I thought
you yourself quoted a paragraph from that spec which says it's
recommended, which means optional.

>> 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.
>>
> 
> This patch fixes the wrong place. In pci_bind_bus_devices(), we have
> the following codes that firstly check if the device is in DT. If not,
> then go on with the driver binding using
> vendor/device/class/subclass... mechanism.
> 
> /* Find this device in the device tree */
> ret = pci_bus_find_devfn(bus, PCI_MASK_BUS(bdf), &dev);
> 
> /* If nothing in the device tree, bind a device */
> if (ret == -ENODEV) {
> ...
> ret = pci_find_and_bind_driver(bus, &find_id, bdf,
>        &dev);
> }
> 
> Your patch adds some codes in pci_find_and_bind_driver() to touch DT,
> which is not the function supposed to do. Hence I call it a hack.

You can call it whatever you want, even repeatedly, but that does not help.

So what do you suggest ?

Mind you, pci_find_and_bind_driver() seems like a perfectly reasonable
place to bind a driver instance and a DT node together in my mind.

>>> 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.
> 
> My suggested fix does not add any OS-specific property. It's one of
> the basic properties defined by DT. Linux works without "compatible"
> in this case that's probably due to Linux was designed to work this
> way. But that does NOT justify we cannot add a "compatible" string to
> make U-Boot's design work.

Hacking up DT to work around bugs in U-Boot PCI code is not an option.
If U-Boot cannot parse a valid DT correctly, then U-Boot needs to be fixed.

It is not because Linux was designed in any way, it is because Linux can
parse DT correctly, including all the details. U-Boot cannot.

>>> 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.
>>>
> 
> [1] https://github.com/devicetree-org/devicetree-specification/releases/tag/v0.2
> [2] http://www.o3one.org/hwdocs/openfirmware/pci_supplement_2_1.pdf
> 
> Regards,
> Bin
> 


-- 
Best regards,
Marek Vasut