Re: [PATCH 9/9] [DNI] ARM: multi_v7_defconfig: Enable CONFIG_ARM_LPAE for multi_v7_config

Alexander Stein
2023-01-19T15:27:46Z

Hi Arnd,

thanks for the fast response.

Am Donnerstag, 19. Januar 2023, 16:09:05 CET schrieb Arnd Bergmann:
> On Thu, Jan 19, 2023, at 15:42, Alexander Stein wrote:
> > This is necessary to support PCIe on LS1021A.
> >
> > Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
>
> Can you explain why this is actually required? I can see that the
> ranges in the PCIe device point to a high address (0x4000000000,
> 2^40), but I can't tell if this is hardwired in the SoC or a
> setting that is applied by software (either the bootloader or
> the PCIe driver).

The RM ([1]) memory map (Table 2-1) says that 'PCI Express 1' is located at
'400000_0000', 'PCI Express 2' at '480000_0000', so I assume this is hardcoded
in SoC.
It also explicitly lists in that table PCIe 1&2 is only accessible with 40-bit
addressing.

> If you can reprogram the memory map, I would expect this to fit
> easily into the 32-bit address space, with 1GB for DDR3 memory
> and 1GB for PCIe BARs.

I'm not sure which part of memory map you can reprogram and where, but I guess
this is fixed on this SoC.

> I don't mind having a defconfig with LPAE enabled, I think this
> can be done using a Makefile target that applies a config
> fragment on top of the normal multi_v7_defconfig, you can find
> some examples in arch/powerpc/configs/*.config.

Ah, nice. This can be a good starter. Thanks.

Best regards,
Alexander

[1] https://www.nxp.com/webapp/Download?colCode=LS1021ARM