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

[Bin Meng]

Hi Tom,

On Tue, Aug 14, 2018 at 1:16 AM, Tom Rini <trini at konsulko.com> wrote:
> On Mon, Aug 13, 2018 at 06:07:14PM +0200, Marek Vasut wrote:
>> On 08/13/2018 03:39 PM, Tom Rini wrote:
>> [...]
>>
>> >>>> Next step is to upstream the DT
>> >>>> changes to Linux kernel, then sync the changes to U-Boot to satisfy
>> >>>> this obsession - using exactly the same DT as Linux.
>> >>>
>> >>> This is not gonna happen.
>> >>>
>> >>> Sorry, you're really just wasting my time with this foolishness. If
>> >>> U-Boot cannot parse valid DT bindings while other OSes can, U-Boot is
>> >>> broken and must be fixed. So far I only see you attacking this patch and
>> >>> trying to pull in everything you can do avoid accepting this patch or
>> >>> providing a better alternative. This is not a constructive discussion,
>> >>> so I stop here.
>> >>
>> >> The fix in this patch is purely hack, period.
>> >
>> > Lets step back for a moment.
>> >
>> > First, U-Boot intends to be, in the case where a relevant DTS file
>> > exists, the Linux kernel one PLUS additions we require (u-boot,dm-spl,
>> > u-boot,dm-pre-reloc, but also sometimes stdout-path or properties that
>> > are omitted for various reasons).
>>
>> Right, which doesn't apply here. None of those u-boot,... props are
>> needed in this case.
>
> Which is why I also mentioned the non-u-boot specific props we also need
> sometimes.  My point is two-fold:
> 1: We can and will _add_ information to the dts files that come from
> Linux.
> 2: Not all information that we add is U-Boot prefixed.
>

It would be better if we document such DT expectation somewhere.

>> > Second, I've asked before (both in this thread and on IRC), and not
>> > gotten an answer yet, as to how Linux goes "Oh, _this_ PCI device and
>> > _this_ DT node need to be matched and populate some data
>> > structures".
>>
>> You did get an answer to that on irc from George. Looks like
>> of_pci_find_child_device() in drivers/pci/of.c
>
> Yeah, George said he thought that might be it but didn't have time to
> confirm.
>
>> > Marek's patch seems to be, in short "here's where U-Boot
>> > needs to wire things up".  Bin has said that no, the function in
>> > question is for other things.
>>
>> I disagree with this. It's a bind function and assigns other parameters
>> of the driver instance too.
>>
>> > I think knowing where Linux does this
>> > would be instructive to figure out where we need to have some additional
>> > logic added OR we can make some cost/benefit analysis to see if it makes
>> > more sense overall to add compatibles to some nodes rather than add to
>> > the binary size.
>>
>> Adding compatible does not make any sense, the PCI ID provides that
>> information. Adding compatible would only add redundancy which could
>> possibly be even harmful (ie. if the controller got replaced with
>> another one).
>
> To try and move things along rather than re-argue the same point, you're
> saying that our pci_find_and_bind_driver() is the rough equivalent of
> of_pci_find_child_device() or at least pci_set_of_node() (which calls
> of_pci_find_child_device()).
>
> So, Bin, if this isn't the right place to start down this path, where
> would be?  Given that Linux can take a DTB and PCI bus with devices and
> get things right, what would it look like for U-Boot to replicate the
> same behavior?  Instead of having to add explicit compatible nodes for
> each PCI device, as I understand (but correct me if I'm wrong) we're
> doing today.  Thanks!

So is this a requirement for all U-Boot driver subsystems to replicate
the same Linux behavior? If yes, can we have it officially documented
somewhere?

Since Marek refused to take the original U-Boot option 1 to support
his case, and asked U-Boot to follow Linux's practice on PCI device
binding, if we go that way, here is what we can do:

* Keep pci-uclass driver's post_bind() and child_post_bind() only for
Sandbox configuration
* Keep the call to pci_bus_find_devfn() in pci_bind_bus_devices() only
for Sandbox configuration
* Sandbox is special. We should limit the mechanism of matching PCI
emulation device via "compatible" to sandbox only
* Assign the DT node to the bound device in pci_find_and_bind_driver()
if there is a valid PCI "reg" encoding for a specific PCI device in
the device tree
* Create DM PCI test case against the DT node assignment
* Remove all compatible string in U-Boot's PCI device drivers: eg:
ehci_pci_ids[], xhci_pci_ids[], etc. IOW, all PCI device drivers
should only use U_BOOT_PCI_DEVICE(), aka the original U-Boot option 2
* Fork a "pci-ns16550" driver to support U_BOOT_PCI_DEVICE(), as
currently PCI ns16550 device driver uses "compatible" string to do the
matching, and update crownbay.dts and galileo.dts (so far I only know
two boards are using PCI ns16550 serial port)
* Make sure all DM PCI test cases are not broken
* Document all of the above changes in doc/driver-model/pci-info.txt

I am not sure if I missed anything. Simon, could you also comment on it?

Regards,
Bin