Re: [PATCH] arm64: dts: marvell: armada-37xx: Increase PCIe IO size from 64 KiB to 1 MiB

[Pali Rohár]

On Friday 18 February 2022 17:43:04 Arnd Bergmann wrote:
> On Thu, Jan 13, 2022 at 6:07 PM Pali Rohár <pali@xxxxxxxxxx> wrote:
> >
> > Commit 514ef1e62d65 ("arm64: dts: marvell: armada-37xx: Extend PCIe MEM
> > space") increased size of PCIe MEM to 127 MiB, which is the maximal
> > possible size for allocated 128 MiB PCIe window. PCIe IO size in that
> > commit was unchanged.
> >
> > Armada 3720 PCIe controller supports 32-bit IO space mapping so it is
> > possible to assign more than 64 KiB if address space for IO.
> >
> > Currently controller has assigned 127 MiB + 64 KiB memory and therefore
> > there is 960 KiB of unused memory. So assign it to IO space by increasing
> > IO window from 64 KiB to 1 MiB.
> >
> > DTS file armada-3720-turris-mox.dts already uses whole 128 MiB space, so
> > only update comment about 32-bit IO space mapping.
> >
> > Signed-off-by: Pali Rohár <pali@xxxxxxxxxx>
> > Fixes: 514ef1e62d65 ("arm64: dts: marvell: armada-37xx: Extend PCIe MEM space")
> 
> I just saw this is the fixes pull request, and it seems very odd. Does this
> fix an actual bug? Note that Linux normally doesn't map more than 64KB
> of I/O space per PCI domain, so it should not make a difference to us.
> 
> Also, note that having a high bus address for the I/O space (0xefff0000,
> as as the CPU physical address here) means that a lot of the older
> devices that actually require I/O space won't work, because they need a
> low bus address in the first few KB.
> 
> Is this mapping a requirement from a broken bootloader, or can you change
> the mapping of the I/O port window in the physical space to the usual
> bus address 0?
> 
>         Arnd

As we discussed on IRC changing mapping of I/O to bus address 0x0 is
possible and together with recent changes of pci-aardvark.c driver
should work out-of-the box.

I sent patch which is changing I/O bus address to 0x0:
https://lore.kernel.org/linux-arm-kernel/20220218212526.16021-1-pali@xxxxxxxxxx/

Please look at it.