From: Sascha Hauer <s.hauer@pengutronix.de>
To: Andrey Smirnov <andrew.smirnov@gmail.com>
Cc: Barebox List <barebox@lists.infradead.org>
Subject: Re: [RFC] ARM: mmu: Do not try to pick early TTB up
Date: Fri, 25 May 2018 11:01:24 +0200 [thread overview]
Message-ID: <20180525090124.wchev5lakkiny2gr@pengutronix.de> (raw)
In-Reply-To: <CAHQ1cqEC7Hpc1k2LEpUzDwk=EipeTLXEO1J0Fk4U7vkZ1MEczA@mail.gmail.com>
On Thu, May 24, 2018 at 08:14:40PM -0700, Andrey Smirnov wrote:
> On Wed, May 23, 2018 at 1:43 AM, Sascha Hauer <s.hauer@pengutronix.de> wrote:
> > On Tue, May 22, 2018 at 10:10:12PM -0700, Andrey Smirnov wrote:
> >> The call to create_flat_mapping() in mmu.c will change both memory
> >> type and shareability of all RAM in use by barebox while MMU is on
> >> when done in conjunction with CONFIG_MMU_EARLY.
> >
> > I notice that with MMU_EARLY enabled we call create_flat_mapping()
> > twice, once in the early MMU code and once when setting up the MMU for
> > real. In between we remap the the SDRAM cached which then is reverted
> > during the second call to create_flat_mapping().
> >
> > This seems unnecessary. Does the following help you?
>
> Yeah, this, disabling MMU before or having a tlb_invalidate() after
> all seem to help. Your patch works fine, but it has a slight weirdness
> in my case because early MMU code would mark OCRAM as cached and
> regular MMU code wouldn't undo it without the call to
> create_flat_mapping(), so I'd end up with slightly different memory
> configuration depending on if EARLY_MMU is enabled or not. Other than
> that it should work fine.
>
> The main reason I chose to go "disable MMU" route is because that
> follows what ARMv8 MMU code does, but I am perfectly happy with either
> solution.
Disabling the MMU probably has a performance impact (I would have to
remeasure, maybe this is not true at all), that's why I would prefer
keeping it enabled.
Sascha
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next prev parent reply other threads:[~2018-05-25 9:01 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-23 5:10 Andrey Smirnov
2018-05-23 8:43 ` Sascha Hauer
2018-05-25 3:14 ` Andrey Smirnov
2018-05-25 9:01 ` Sascha Hauer [this message]
2018-05-25 9:09 ` Lucas Stach
2018-05-25 17:07 ` Andrey Smirnov
2018-05-25 17:09 ` Andrey Smirnov
2018-05-25 17:35 ` Sam Ravnborg
2018-05-28 12:05 ` Sascha Hauer
2018-05-28 18:08 ` Andrey Smirnov
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