linux-kernel - RE: [PATCH v4] ARM: configs: Add Freescale LS1021A defconfig

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Message-ID: <BN3PR0301MB0867A87B64E1206B773F05EEFE3E0@BN3PR0301MB0867.namprd03.prod.outlook.com>
Date:	Thu, 15 Oct 2015 02:11:57 +0000
From:	Huan Wang <alison.wang@...escale.com>
To:	Arnd Bergmann <arnd@...db.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
CC:	Jin Jason <Jason.Jin@...escale.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Fabio Estevam <festevam@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"shawnguo@...nel.org" <shawnguo@...nel.org>
Subject: RE: [PATCH v4] ARM: configs: Add Freescale LS1021A defconfig

> On Wednesday 14 October 2015 10:18:47 Huan Wang wrote:
> > > On Thursday 24 September 2015 07:27:10 Huan Wang wrote:
> > > > > On Fri, Sep 18, 2015 at 4:38 AM, Huan Wang
> > > > > <alison.wang@...escale.com>
> > > > > wrote:
> > > > >
> > > > > > [Alison Wang] Thanks for your reply. I agreed with you about
> > > > > > creating a new multi_v7_lpae_defconfig. In
> > > > > > multi_v7_lpae_defconfig, I need to add the following CONFIG_XX
> > > > > > to support LS1021A based on
> > > > > multi_v7_defconfig.
> > > > > >
> > > > > > CONFIG_ARM_LPAE=y
> > > > > > CONFIG_VMSPLIT_2G=y
> > > > >
> > > > > Is CONFIG_VMSPLIT_2G=y really needed?
> > > > [Alison Wang] I tried to remove CONFIG_VMSPLIT_2G and used the
> > > > default CONFIG_VMSPLIT_3G, but kernel could not boot up. It hangs
> > > > at " Starting
> > > kernel ... ".
> > > >
> > > > Any suggestion? Thanks.
> > >
> > > Try enabling DEBUG_LL for your platform to get some debug output, if
> > > you still don't get any helpful messages, try also inserting
> > >
> > >       printascii(__func__);
> > >
> > > statements in the early boot process to see how far you get before the
> hang.
> > >
> > [Alison Wang] I can get to __turn_mmu_on or later, but I could not get
> > the print message "Booting Linux on physical CPU 0xf00" in
> smp_setup_processor_id().
> >
> > I guess something wrong with the initial page tables in
> > __create_page_tables, as for CONFIG_VMSPLIT_3G, only PAGE_OFFSET is
> changed from 0x80000000 to 0xC0000000.
> > BTW, on our platform, TEXT_OFFSET is 0x00008000, PHYS_OFFSET is
> 0x80000000.
> >
> > Any suggestion? Thanks.
> 
> My first guess is that there is something wrong with your debug_ll
> implementation, as that would explain why you can't get anything to the
> console after turning on page tables.
> 
> It looks like ls1021a uses lpuart, but I can't even see an implementation
> for that in arch/arm/include/debug/. What code do you use for printing?
> 
[Alison Wang] ls1021a uses duart as the default serial port, not lpuart. So
8250/16550 serial driver is used. Let me explain my debug process in detail.

When CONFIG_VMSPLIT_2G is used, I could boot up the whole kernel and get the
print message " Booting Linux on physical CPU 0xf00" after "Starting kernel"
as below.

Starting kernel ...
[    0.000000] Booting Linux on physical CPU 0xf00
.....

But when CONFIG_VMSPLIT_3G is used, I couldn't get print message " Booting Linux
on physical CPU 0xf00". It only hangs at  "Starting kernel ...".

Moreover, I add some asm code in __turn_mmu_on to print some simple characters, and
I could get the print characters when CONFIG_VMSPLIT_3G is used. So I guess there
is something wrong with the page tables.


Best Regards,
Alison Wang
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