Re: [PATCH] arm64: dts: marvell: armada-37xx: Remap IO space to bus address 0x0

["Marek Behún" <kabel@kernel.org>]

On Wed, 2 Mar 2022 14:15:15 +0100
Marek Behún <kabel@kernel.org> wrote:

> On Wed, 2 Mar 2022 14:06:01 +0100
> Andrew Lunn <andrew@lunn.ch> wrote:
> 
> > On Tue, Mar 01, 2022 at 10:25:39AM +0100, Pali Rohár wrote:  
> > > On Monday 28 February 2022 17:42:03 Gregory CLEMENT wrote:    
> > > > > Hello Pali,
> > > > >    
> > > > >> Remap PCI I/O space to the bus address 0x0 in the Armada 37xx
> > > > >> device-tree in order to support legacy I/O port based cards which have
> > > > >> hardcoded I/O ports in low address space.
> > > > >>
> > > > >> Some legacy PCI I/O based cards do not support 32-bit I/O addressing.
> > > > >>
> > > > >> Since commit 64f160e19e92 ("PCI: aardvark: Configure PCIe resources from
> > > > >> 'ranges' DT property") this driver can work with I/O windows which
> > > > >> have    
> > > > >
> > > > > Should we add a "Fixes: 64f160e19e92 ("PCI: aardvark: Configure PCIe
> > > > > resources from 'ranges' DT property")" tag ?    
> > > > 
> > > > Waiting for your confirmation I tried to applied it but it failed.
> > > > 
> > > > Did you base this patch on v5.17-rc1 ?
> > > > 
> > > > Gregory    
> > > 
> > > Hello! This change is breaking booting of Turris Mox kernel with older
> > > bootloader due to bugs in bootloader.    
> > 
> > Do you know what actually goes wrong?
> > 
> > I've not been involved in the discussion, but looking at the comments
> > above, not changing the space can result in non-working cards. So it
> > does sound like something which in general we want to do. Does the
> > current code assume the bootloader has initialized some registers with
> > specific values? Can that be moved into the driver so it also works
> > with older bootloaders?  
> 
> No. TF-A may remap CPU PCIe window, and so U-Boot fixes these addresses
> in device-tree. But the fixup function was at first written in such a
> way that it assumes that the ranges propreties contains specific
> values. The proposed DT change, together with the fixup function in
> older U-Boot, will break ranges property to non-functional state.
> 
> See corresponding U-Boot patches
> 
> https://patchwork.ozlabs.org/project/uboot/patch/20200408172522.18941-5-marek.behun@nic.cz/
> https://patchwork.ozlabs.org/project/uboot/patch/20210526155940.26141-5-pali@kernel.org/
> https://patchwork.ozlabs.org/project/uboot/patch/20220223125232.7974-1-kabel@kernel.org/
> 
> The last patch is not merged yet.

To explain more:
- the first patch added the ranges property fixup. After that patch
  (which was applied sometime not long after 8th April 2020) U-Boot
  fixes the ranges property in a way that does not work with the
  proposed DT change.
- the second patch extended the fixup, but it still won't work
  correctly with the proposed DT change
- the third U-Boot patch will fix this issue, afterwards the DT change
  won't break PCIe. This patch is not yet merged in U-Boot

It is questionable how many users have updated U-Boot to the version
with first fixup. AFAIK we at Turris did not make an automatic update
for U-Boot yet for Turris MOX, it was done manually only for some
boards that had some problems or users wanted certain features.

But we can't change the device-tree because it will break the
functinality for some users.

What we could do is add another patch to U-Boot that would change IO
window address if certain conditions are met (for example if the ranges
proprety was not changed by the user and thus contains a specific
value that can be checked for).

Marek

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