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

Bin Meng
2018-08-13T02:24:01Z

Hi Marek,

On Fri, Aug 10, 2018 at 8:38 PM, Marek Vasut <marek.vasut@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@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.
>>
>> 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:

- 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.

>> 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