Re: [PATCH 3/5] MIPS: Loongson64: Enlarge IO_SPACE_LIMIT

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在 2020/7/20 下午6:45, Arnd Bergmann 写道:
On Mon, Jul 20, 2020 at 9:44 AM Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx> wrote:
It can be very big on LS7A PCH systems.

Signed-off-by: Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx>
---
   * On MIPS I/O ports are memory mapped, so we access them using normal
diff --git a/arch/mips/include/asm/mach-loongson64/spaces.h b/arch/mips/include/asm/mach-loongson64/spaces.h
index 3de0ac9d8829..b99b43854929 100644
--- a/arch/mips/include/asm/mach-loongson64/spaces.h
+++ b/arch/mips/include/asm/mach-loongson64/spaces.h
@@ -11,8 +11,7 @@
  #define PCI_IOSIZE     SZ_16M
  #define MAP_BASE       (PCI_IOBASE + PCI_IOSIZE)

-/* Reserved at the start of PCI_IOBASE for legacy drivers */
-#define MMIO_LOWER_RESERVED    0x10000
+#define IO_SPACE_LIMIT 0x00ffffff
Does this mean that firmware may already have assigned "high" I/O space
numbers for devices? I'm not sure how well device drivers can generally
deal with port numbers that don't fit into a 16-bit integer.
Limited test shows most drivers can deal with that. But We'll aware the problem,
thanks for the remind.

Is it possible to run a 32-bit kernel on these machines? If yes, than
taking up 16MB of virtual addresses may also become a problem.

We've killed the ability of running 32-bit kernel on MACH_LOONGSON64.

In practice, one should rarely need more than a few kb worth of
port numbers, unless you expect to see hundreds of legacy PCI
devices.
I must blame stupid hardware design here. The LPC Controller (for ISA device) can eat up to 0x20000 IO BAR, and we can't resize it. Thus we have to enlarge the I/O Space.

Thanks!

- Jiaxun

        Arnd



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