linux-kernel - Re: [RFC] On the Current Troubles of Mainlining Loongson Platform Drivers

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Message-ID: <orwolaw5u1.fsf@lxoliva.fsfla.org>
Date:   Thu, 07 Mar 2019 21:46:46 -0300
From:   Alexandre Oliva <lxoliva@...la.org>
To:     "Maciej W. Rozycki" <macro@...ux-mips.org>
Cc:     Aaro Koskinen <aaro.koskinen@....fi>, Tom Li <tomli@...li.me>,
        James Hogan <jhogan@...nel.org>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Huacai Chen <chenhc@...ote.com>,
        Ralf Baechle <ralf@...ux-mips.org>, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC] On the Current Troubles of Mainlining Loongson Platform Drivers

On Mar  7, 2019, "Maciej W. Rozycki" <macro@...ux-mips.org> wrote:

>  So this seems backwards to me, port I/O is supposed to be strongly 
> ordered, so if removing the ordering guarantee "fixes" your problem, then 
> there must be a second bottom here.

Well, it partially restores the earlier state, so the actual bug goes
back to latent.  We just have to find out what it is.  My plan, in the
next time slot I can devote to this investigation, is to try to bisect
source files that use these interfaces to identify a minimal set that
can switch to the new barriers without breaking anything, then report
back after failing to make sense of it myself ;-)  So, yeah, several
more bottoms to dig through.

> Does your platform use `war_io_reorder_wmb'?

Err...  I'm not sure I understand your question.

It uses it in __BUILD_IOPORT_SINGLE within the expanded out function,
given !barrier, but you already knew that.

Did you mean to ask what war_io_reorder_wmb expand to, or whether there
are other uses of war_io_reorder_wmb, or what?

-- 
Alexandre Oliva, freedom fighter   https://FSFLA.org/blogs/lxo
Be the change, be Free!         FSF Latin America board member
GNU Toolchain Engineer                Free Software Evangelist
Hay que enGNUrecerse, pero sin perder la terGNUra jamás-GNUChe