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From:   Greentime Hu <green.hu@gmail.com>
Date:   Mon, 22 Jan 2018 23:20:28 +0800
Message-ID: <CAEbi=3dZ-Bj+pdhcu1Td1JzgDngyMMeDTFs=XH3LNPnudcUGyg@mail.gmail.com>
Subject: Re: [PATCH v6 29/36] nds32: Build infrastructure
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Greentime <greentime@andestech.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Jason Cooper <jason@lakedaemon.net>,
        Marc Zyngier <marc.zyngier@arm.com>,
        Rob Herring <robh+dt@kernel.org>,
        Networking <netdev@vger.kernel.org>,
        Vincent Chen <deanbo422@gmail.com>,
        DTML <devicetree@vger.kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        David Howells <dhowells@redhat.com>,
        Will Deacon <will.deacon@arm.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        linux-serial@vger.kernel.org,
        Geert Uytterhoeven <geert.uytterhoeven@gmail.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Mark Rutland <mark.rutland@arm.com>, Greg KH <greg@kroah.com>,
        Guo Ren <ren_guo@c-sky.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        David Miller <davem@davemloft.net>,
        Jonas Bonn <jonas@southpole.se>,
        Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>,
        Stafford Horne <shorne@gmail.com>,
        Vincent Chen <vincentc@andestech.com>
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Hi, Arnd:

2018-01-18 19:00 GMT+08:00 Arnd Bergmann <arnd@arndb.de>:
> On Mon, Jan 15, 2018 at 6:53 AM, Greentime Hu <green.hu@gmail.com> wrote:
>> From: Greentime Hu <greentime@andestech.com>
>>
>> This patch adds Makefile, Kconfig and vmlinux.lds.S files required for building
>> an nds32 kernel.
>>
>> Signed-off-by: Vincent Chen <vincentc@andestech.com>
>> Signed-off-by: Greentime Hu <greentime@andestech.com>
>
> I find some new details every time I look here ;-)

Thank you for revewing so detailedly. :)

>> @@ -0,0 +1,107 @@
>> +#
>> +# For a description of the syntax of this configuration file,
>> +# see Documentation/kbuild/kconfig-language.txt.
>> +#
>> +
>> +config NDS32
>> +        def_bool y
>> +       select ARCH_HAS_RAW_COPY_USER
>
> I don't think this symbol was ever merged. Do you remember why you added it?

I will drop it. It must be added in earlier kernel version.

>> +       select ARCH_WANT_FRAME_POINTERS if FTRACE
>> +       select ARCH_WANT_IPC_PARSE_VERSION
>
> You most certainly don't want IPC_PARSE_VERSION, please drop this
> and adapt your glibc.

ok. I will drop it.

>> +       select CLKSRC_MMIO
>> +       select CLONE_BACKWARDS
>> +       select COMMON_CLK
>> +       select FRAME_POINTER
>
> Do you need both ARCH_WANT_FRAME_POINTERS and FRAME_POINTER here?

I will drop FRAME_POINTER.

>> +       select GENERIC_ATOMIC64
>> +       select GENERIC_CPU_DEVICES
>> +       select GENERIC_CLOCKEVENTS
>> +       select GENERIC_IRQ_CHIP
>> +       select GENERIC_IRQ_PROBE
>
> I think it's better to drop GENERIC_IRQ_PROBE here, no modern driver
> should rely on that.

I will drop it.

>> +choice
>> +       prompt "CPU type"
>> +       default CPU_V3
>> +config CPU_N15
>> +       bool "AndesCore N15"
>> +config CPU_N13
>> +       bool "AndesCore N13"
>> +       select CPU_CACHE_ALIASING if ANDES_PAGE_SIZE_4KB
>> +config CPU_N10
>> +       bool "AndesCore N10"
>> +       select CPU_CACHE_ALIASING
>> +config CPU_D15
>> +       bool "AndesCore D15"
>> +config CPU_D10
>> +       bool "AndesCore D10"
>> +       select CPU_CACHE_ALIASING
>> +config CPU_V3
>> +       bool "AndesCore v3 compatible"
>> +       select ANDES_PAGE_SIZE_8KB
>> +endchoice
>
> I forget what we discussed here earlier, but at the very least, there should be
> some help text here to explain what the implications are. I assume that you
> generally want to be able to build one kernel to run on all of the above, right?
>
> Will selecting 'CPU_V3' result in a kernel binary that can run on all of them?
> If so, please explain it here as that is not obvious.
>
> For the other CPU types, can you list the what backwards-compatiblity
> you get? E.g. will a kernel built for N13 run on any of N15, D15 or N10?
>
Yes, we would like to build a kernel with CPU_V3 to run on all of the above.

Not sure if these help texts clear enough?

choice
        prompt "CPU type"
        default CPU_V3
        help
          The data cache of N15/D15 is implemented as PIPT and it will
not cause the
          cache aliasing issue. The rest cpus(N13, N10 and D10) are
implemented as
          VIPT data cache. It may cause the cache aliasing issue if
its cache way
          size is larger than page size. You can specify the the CPU
type direcly or
          choose CPU_V3 if unsure.

          A kernel built for N10 is able to run on N15, D15, N13, N10 or D10.
          A kernel built for N15 is able to run on N15 or D15.
          A kernel built for D10 is able to run on D10 or D15.
          A kernel built for D15 is able to run on D15.
          A kernel built for N13 with CPU_CACHE_ALIASING is able to
run on N15, D15, N13, N10 or D10
          A kernel built for N13 without CPU_CACHE_ALIASING is able to
run on N15, N13 or D15

config CPU_N15
        bool "AndesCore N15"
config CPU_N13
        bool "AndesCore N13"
        select CPU_CACHE_ALIASING if ANDES_PAGE_SIZE_4KB
config CPU_N10
        bool "AndesCore N10"
        select CPU_CACHE_ALIASING
config CPU_D15
        bool "AndesCore D15"
config CPU_D10
        bool "AndesCore D10"
        select CPU_CACHE_ALIASING
config CPU_V3
        bool "AndesCore v3 compatible"
        select CPU_CACHE_ALIASING
endchoice

> I think the 'select ANDES_PAGE_SIZE_8KB' cannot work as expected,
> since ANDES_PAGE_SIZE_8KB is inside of a 'choice' statement. Since
> there are only two options (4K and 8K), you can address that by making
> it a simple bool option and fall back to 4K when ANDES_PAGE_SIZE_8KB
> is disabled.

After reviewing this config, it seems to make much more sense if we
select CPU_CACHE_ALIASING.
A kernel with aliasing cache handling should be able to run on
aliasing/non-aliasing CPU.

config CPU_V3
        bool "AndesCore v3 compatible"
        select CPU_CACHE_ALIASING

>> +config CACHE_L2
>> +       bool "Support L2 cache"
>> +        default y
>> +       help
>> +         Say Y here to enable L2 cache if your SoC are integrated with L2CC.
>> +         If unsure, say N.
>> +
>> +menu "Memory configuration"
>> +
>> +choice
>> +       prompt "Memory split"
>> +       depends on MMU
>> +       default VMSPLIT_3G
>
> Why not default to VMSPLIT_3G_OPT?
>

I will set default to VMSPLIT_3G_OPT and delete
CONFIG_VMSPLIT_3G_OPT=y in defconfig.