RE: PCIE on LS1021A

[Renaud Barbier <Renaud.Barbier@ametek.com>]

Hello Ahmad,
This has been a while that I asked you about a question on the PCIE for the LS1021A.
We are developing a new product with a NVME device using the LS1021A CPU and
I would like to add LPAE support to barebox so that PCI child devices can be probed.

I am trying to figure out how to assemble LPAE support based on the information you gave me below and what I see in U-boot.

A grep of LPAE in U-boot shows several files with specific code for LPAE:
arch/arm/cpu/armv7/start.S
arch/arm/lib/cache-cp15.c
arch/arm/cpu/armv7/ls102xa/cpu.c

I do  recognize similar pieces of code between barebox and U-boot
From the message below, I understand I would need to update map_io_sections to map the PCI address as in U-boot mmu_setup from the file arch/arm/cpu/armv7/ls102xa/cpu.c

Cheers,
Renaud



> -----Original Message-----
> From: Ahmad Fatoum <a.fatoum@pengutronix.de>
> Sent: 09 December 2022 19:18
> To: Renaud Barbier <Renaud.Barbier@ametek.com>; Barebox List
> <barebox@lists.infradead.org>
> Cc: Lucas Stach <lst@pengutronix.de>
> Subject: Re: PCIE on LS1021A
> 
> ***NOTICE*** This came from an external source. Use caution when
> replying, clicking links, or opening attachments.
> 
> On 09.12.22 19:37, Ahmad Fatoum wrote:
> >> From my debugging I can see that the Layerscape PCIE driver use VA
> >> address = PA address = 0x24000000
> >>
> >> So  Is the problem I am seeing an issue with mapping the correct physical
> address for a 32-bit processor?
> >>
> >> If yes, how can I map the 64-bit PA to a 32-bit VA?
> >
> > Normally, you would call map_io_sections as pci-tegra does, but in
> > your case this alone is insufficient as you will need to implement
> > ARM32 LPAE support first. Once that's in place, you can use
> > map_io_sections and map it to e.g. 0x24000000 as U-Boot does
> arch/arm/cpu/armv7/ls102xa/cpu.c mmu_setup().
> >
> > U-Boot LPAE support was added to support Rpi2, which starts in HYP
> > mode, but we had worked around that in barebox to not require LPAE.
> > For your case however, I don't believe there's a way around using LPAE
> page tables.
> >
> > Tangentially related: I don't know how the PCI controller maintains
> > cache coherency, but if it does write back through CPU caches, you may
> observe memory corruption.
> >
> > It may be the safest for you to disable cache snooping for PCIe until
> > that's resolved (We've this planned, but it will probably not happen this
> year.
> > If you're interested I can elaborate).
> 
> I should have shortened the context a bit. Posting again in case you missed
> it.
> 
> >
> > Cheers,
> > Ahmad
> >
> >
> >
> >>
> >> Cheers,
> >> Renaud
> >>
> >>
> >>
> >>
> >>
> >
> 
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