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

Tue Aug 14 01:46:45 UTC 2018

Hi Marek,

On Mon, Aug 13, 2018 at 9:46 PM, Marek Vasut <marek.vasut at gmail.com> wrote:
> On 08/13/2018 04:24 AM, Bin Meng wrote:
>> Hi Marek,
>>
>> On Fri, Aug 10, 2018 at 8:38 PM, Marek Vasut <marek.vasut at gmail.com> wrote:
>>> On 08/10/2018 02:01 PM, Tom Rini wrote:
>>>> On Wed, Aug 08, 2018 at 09:37:25PM +0200, Marek Vasut 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 at 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 at 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 at 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 at gmail.com>
>>>>>>>>>>> Cc: Simon Glass <sjg at 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.
>>>>
>>>> DT should but isn't always OS agnostic.  DTS files that reside in the
>>>> Linux Kernel are in practice is Linux-centric with the expectation that
>>>> even if you could solve a given problem with valid DTS changes you make
>>>> whatever is parsing it do additional logic instead.  That,
>>>> approximately, is what your patch is doing.  If you added some HW
>>>> description information to the dtsi file everything would work as
>>>> expected as your DTS is describing the hardware and U-Boot is reading
>>>> that description and figuring out what to do with it.
>>>
>>> Yes, you need additional logic to match the PCI controller subnode in DT
>>> with PCI device BFD, that's expected. You do NOT need extra compatibles,
>>> the PCI bus gives you enough information to match a driver on them. In
>>> fact, adding a compatible can interfere with this matching.
>>>
>>
>> Please, read U-Boot's doc/driver-model/pci-info.txt. You really don't
>> understand current implementation in U-Boot. In short, U-Boot supports
>> two scenarios for PCI driver binding:
>
> That documentation is wrong and needs to be fixed. The compatible is
> optional.
>

No it is not wrong. The documentation reflects the update-to-date
U-Boot support of PCI bus with DM.

>> - Declare a PCI device in the device tree. That requires specifying a
>> 'compatible' string as well as 'reg' property as defined by the 'PCI
>> Bus Binding' spec. DM uses the 'compatible' string to bind the driver
>> for the device.
>> - Don't declare a PCI device in the device tree. Instead, using
>> U_BOOT_PCI_DEVICE() to declare a device and driver mapping.
>>
>> You can choose either two when you support PCI devices on your board,
>> but you cannot mix both support together and make them a mess. In this
>> patch, you hacked pci_find_and_bind_driver() which is the 2nd scenario
>> to support the 1st scenario.
>
> Again, the DT contains all the required information to bind the node and
> the driver instance. Clearly, we need option 3 for this.
>

Then that's a new design proposal. Anything that wants to mess up
current design is a hack.

>>>> The problem here is that in Linux, something that sees the compatible
>>>> renesas,pci-r8a7794 or renesas,pci-rcar-gen2 is doing whatever else
>>>> needs to be done.  Or something else?  Please explain how what you want
>>>> to have work here in U-Boot is working in the Linux kernel.  Thanks!
>>>
>>> This has nothing to do with a specific controller. iMX6 does the same
>>> thing, see ie arch/arm/boot/dts/imx6q-utilite-pro.dts .

Regards,
Bin