Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20200720074249.596364-1-jiaxun.yang@flygoat.com> <20200720074249.596364-4-jiaxun.yang@flygoat.com>
In-Reply-To: <20200720074249.596364-4-jiaxun.yang@flygoat.com>
From:   Arnd Bergmann <arnd@arndb.de>
Date:   Mon, 20 Jul 2020 12:45:14 +0200
Message-ID: <CAK8P3a13vZJyOGZ1FpS98ytVC57P6NgmQpSfhf2h9b7meQLtcw@mail.gmail.com>
Subject: Re: [PATCH 3/5] MIPS: Loongson64: Enlarge IO_SPACE_LIMIT
To:     Jiaxun Yang <jiaxun.yang@flygoat.com>
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>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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.

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.

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.

       Arnd