linux-kernel - Re: [PATCH] arm: Add Arm Erratum 773769 for Large data RAM latency.

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Message-id: <alpine.LFD.2.10.1401081600370.1851@knanqh.ubzr>
Date:	Wed, 08 Jan 2014 16:08:42 -0500 (EST)
From:	Nicolas Pitre <nico@...xnic.net>
To:	Doug Anderson <dianders@...omium.org>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Will Deacon <will.deacon@....com>,
	Vivek Gautam <gautam.vivek@...sung.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	"kgene.kim@...sung.com" <kgene.kim@...sung.com>,
	"sboyd@...eaurora.org" <sboyd@...eaurora.org>,
	David Garbett <David.Garbett@....com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"gregory.clement@...e-electrons.com" 
	<gregory.clement@...e-electrons.com>,
	Olof Johansson <olofj@...omium.org>
Subject: Re: [PATCH] arm: Add Arm Erratum 773769 for Large data RAM latency.

On Wed, 8 Jan 2014, Doug Anderson wrote:

> Hi,
> 
> On Wed, Jan 8, 2014 at 11:20 AM, Russell King - ARM Linux
> > No, we're saying to put the work-around in the boot loader, not the kernel.
> 
> Unfortunately the resume path of the firmware runs from Read Only 
> firmware code (yes, it sucks), so it's not totally trivial to fix. It 
> would be possible for someone to unscrew their write protect switch 
> and update their RO firmware, but that doesn't help the average user.

[...]

> I'd guess that the way forward is:
> 
> * Land kernel workaround locally in Chromium tree
> 
> * I'll try to land FW change locally in at least one Chromium branch.
> If we were to get a new RO build ever (seems unlikely at this point)
> it would be fixed for upstream kernels.  If we were to get a new RW
> build (seems unlikely, but at least less unlikely) it would be fixed
> if someone landed a kernel patch to save/restore this register across
> suspend/resume.
> 
> * If Joe Upstream wants to run an upstream kernel on some type of
> exynos5250 product (Samsung ARM Chromebook, HP Chromebook 11, Nexus 10
> are the ones I know of) then he will deal with the small number of
> crashes or figure out a solution.

If Joe Upstream wants to run an upstream kernel, doesn't he have to 
unscrew his write protect switch first, at which point the RO firmware 
can be updated as well?


Nicolas
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