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Subject: Re: [PATCH] MIPS: Introduce cmdline argument writecombine=
To:     Tiezhu Yang <yangtiezhu@loongson.cn>
Cc:     Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Huacai Chen <chenhc@lemote.com>, linux-mips@vger.kernel.org,
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From:   Jiaxun Yang <jiaxun.yang@flygoat.com>
Message-ID: <c81440ec-a46e-06e1-9ee3-ec3bd2826c4e@flygoat.com>
Date:   Fri, 7 Aug 2020 02:26:03 +0800
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在 2020/8/7 上午12:52, Thomas Bogendoerfer 写道:
> On Thu, Aug 06, 2020 at 07:56:20PM +0800, Jiaxun Yang wrote:
>> Our current problem is Loongson's writecombine implementation seems buggy.
>> This is our platform issue rather than target hardware issue.
> ok, so simply clear cpu_data[0].writecombine for the fauly parts
@Tiezhu,

I don't know the exact faulty parts, could you please investigate it in 
Loongson?

I can remember a Loongson stuff told me the issue was solved in GS464E but
there are still users complaining about that.

In fact I can't reproduce it in all of my test systems:
3B1500 + RS780E + R5 230
3A3000 + RS780E Laptop
3A4000 + LS7A + RX550
>> And we don't even know which hardware is known to be good. The same graphic
>> card became a different story on different user's hand.
> find out what is broken and add the needed workarounds then.

Well, let's leave this task for Loongson company.
User's community don't have the ability to trace hardware behavior 
precisely.

>> I understood what Teizhu thought. For entry-level users, we don't want to
>> trouble
>> them, so we have writecombine disabled by default. However, for advanced
>> user
>> trying to tweak their system, we should leave a switch for them to get it
>> back.
> IMHO if we do it that way, we end up with millions of knobs for tweaking
> broken hardware, and nobody knows what's exactly broken. Sorry I won't go
> that way.

Haha, that was my first impression to Linux as a primary school student. 
It just
looks like an aircraft cockpit with thousands of knobs & switches, but 
to airborne
you just need to control yoke and throttle.

- Jiaxun