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Subject: Re: [PATCH 3/5] MIPS: Loongson64: Enlarge IO_SPACE_LIMIT
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     "open list:BROADCOM NVRAM DRIVER" <linux-mips@vger.kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Huacai Chen <chenhc@lemote.com>,
        Frank Rowand <frowand.list@gmail.com>,
        Paul Burton <paulburton@kernel.org>,
        Nathan Chancellor <natechancellor@gmail.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        DTML <devicetree@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20200720074249.596364-1-jiaxun.yang@flygoat.com>
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 <CAK8P3a13vZJyOGZ1FpS98ytVC57P6NgmQpSfhf2h9b7meQLtcw@mail.gmail.com>
From:   Jiaxun Yang <jiaxun.yang@flygoat.com>
Message-ID: <d927b5b6-e33e-4a94-c997-b1794dbde411@flygoat.com>
Date:   Mon, 20 Jul 2020 20:04:22 +0800
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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@flygoat.com> wrote:
>> It can be very big on LS7A PCH systems.
>>
>> Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
>> ---
>>    * 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