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

[Jiaxun Yang]

å 2020/7/20 äå6:45, Arnd Bergmann åé:
> 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