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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Wed, 28 Aug 2019 15:02:36 +0200
Message-ID: <CAK8P3a1PeBMRuweAmzrTQC85CmwdZPirG3HPg9aJ99p2U7zknQ@mail.gmail.com>
Subject: Re: [PATCH 14/22] ARM: omap1: use pci_ioremap_io() for omap_cf
To:     Aaro Koskinen <aaro.koskinen@iki.fi>
Cc:     Tony Lindgren <tony@atomide.com>,
        Dominik Brodowski <linux@dominikbrodowski.net>,
        linux-omap <linux-omap@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        Tomi Valkeinen <tomi.valkeinen@ti.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Tue, Aug 27, 2019 at 9:05 PM Aaro Koskinen <aaro.koskinen@iki.fi> wrote:
> On Tue, Aug 27, 2019 at 06:33:01PM +0200, Arnd Bergmann wrote:
> > On Fri, Aug 16, 2019 at 10:34 AM Aaro Koskinen <aaro.koskinen@iki.fi> wrote:
> > > However with earlyprintk it seems to hang as soon as kernel tries to print
> > > something. So something goes wrong with early DEBUG_LL mapping code when
> > > CONFIG_DEBUG_UART_VIRT=0xff000000 is used?
> >
> > I just redid the calculation and came out with the same address, so I
> > don't think I put the wrong one there. The address also does not
> > conflict with the PCI mapping, and the address is the same one that
> > is installed later, so that should also be fine.
> >
> > Are you sure you used the correct address in the .config file? If you
> > ran 'make oldconfig', the virtual address would not be changed here
> > as I just modify the default for a fresh 'make omap1_defconfig'
> > run or similar.
>
> Yes... You should be able to try this out also in QEMU to see the hang:

Haven't tried yet, but I took a look at the dump:

> $ qemu-system-arm -M sx1 -kernel sx1-zImage -nographic
>
> [ Hangs silently, press Ctrl-a c to enter monitor. ]
>
> QEMU 4.1.0 monitor - type 'help' for more information
> (qemu) info registers
> R00=c0379de1 R01=0000005b R02=00000000 R03=ff000000
> R04=00000000 R05=00000031 R06=c038f119 R07=00000000
> R08=00000000 R09=c038f50e R10=600001d3 R11=00000001
> R12=00000010 R13=c0379de0 R14=c000e07c R15=c000dfcc
> PSR=000001d3 ---- A svc32
> FPSCR: 00000000
>
> from System.map:
> c000df7c T printascii
> c000dfe0 T printch

Ok, that is clearly the "busyloop" macro in
arch/arm/include/debug/8250.S, checking if the data got sent.

The 'r2' register contains zero, so UART_LSR_TEMT and
UART_LSR_THRE are not set, but presumably the mapping
was installed right since you did not get a page fault.

I assume you checked that the uart output wasn't already broken
by one of the earlier patches, right?

Also, looking at arch/arm/mach-omap1/include/mach/uncompress.h
it seems that SX1 normally uses UART3, not UART1.
Is that different in qemu?

        Arnd