linux-kernel - Re: [PATCH v1] ARM: tegra: Fix misplaced tegra_uart

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Message-ID: <b8de29b7-b0f6-5b2b-6ab2-f4399bc241fc@gmail.com>
Date:   Tue, 15 Dec 2020 10:22:16 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Ard Biesheuvel <ardb@...nel.org>
Cc:     linux-tegra@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] ARM: tegra: Fix misplaced tegra_uart_config in
 decompressor



On 12/15/2020 8:53 AM, Dmitry Osipenko wrote:
> 15.12.2020 19:40, Florian Fainelli пишет:
>>
>>
>> On 12/15/2020 8:17 AM, Dmitry Osipenko wrote:
>>> 15.12.2020 19:04, Florian Fainelli пишет:
>>>>
>>>>
>>>> On 12/15/2020 5:52 AM, Dmitry Osipenko wrote:
>>>>> The tegra_uart_config of the DEBUG_LL code is now placed right at the
>>>>> start of the .text section after commit which enabled debug output in the
>>>>> decompressor. Tegra devices are not booting anymore if DEBUG_LL is enabled
>>>>> since tegra_uart_config data is executes as a code. Fix the misplaced
>>>>> tegra_uart_config storage by embedding it into the code.
>>>>>
>>>>> Cc: stable@...r.kernel.org
>>>>> Fixes: 2596a72d3384 ("ARM: 9009/1: uncompress: Enable debug in head.S")
>>>>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>>>>> ---
>>>>>  arch/arm/include/debug/tegra.S | 54 +++++++++++++++++-----------------
>>>>>  1 file changed, 27 insertions(+), 27 deletions(-)
>>>>
>>>> Looks like arch/arm/include/debug/brcmstb.S would need the same
>>>> treatment since the implementation was copied from tegra.S.
>>>>
>>>
>>> Good catch, will you be able to test the brcm and make a patch?
>>
>> Yes, absolutely, building a kernel to test right now.
>>
> 
> Thank you.
> 
> BTW, I noticed that the problem is more visible on a thumb2 kernel
> build, i.e. you should get a more reliable hang on boot. On a non-thumb2
> kernel the hanging behaviour seems depends on a device / bootloader. I
> haven't tried to figure out what exactly makes the difference, perhaps
> it should be a memory layout / state.

To build with a CONFIG_THUMB2_KERNEL I had to fetch:

https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9018/2

to avoid a build error, too bad this missed v5.10 final but hopefully it
can make it soon.

With CONFIG_THUMB2_KERNEL=y, I am not getting the head.S output where it
prints the start/end of the compressed kernel:

C:0x420800C0-0x4321B0E0->0x4212AB00-0x432C5B20
Uncompressing Linux... done, booting the kernel.
[    0.000000] Booting Linux on physical CPU 0x0
[    0.000000] Linux version 5.10.0-g148842c98a24
(fainelli@...nelli-desktop) (arm-linux-gcc (GCC) 8.3.0, GNU ld (GNU
Binutils) 2.32) #71 SMP Tue Dec 15 09:53:09 PST 2020

I am only getting:

Uncompressing Linux... done, booting the kernel.

Is that the same for you?

Looking at the disassembly of head.o it definitively has
brcmstb_uart_config in the .text section as the beginning just like you
mentioned in your commit message.

Disassembly of section .text:

00000000 <brcmstb_uart_config>:
   0:   00000001        andeq   r0, r0, r1
        ...
   c:   467c            mov     r4, pc
   e:   f004 4478       and.w   r4, r4, #4160749568     ; 0xf8000000
  12:   f504 4400       add.w   r4, r4, #32768  ; 0x8000
  16:   4678            mov     r0, pc
  18:   42a0            cmp     r0, r4
  1a:   bf3f            itttt   cc
  1c:   48d4            ldrcc   r0, [pc, #848]  ; (370 <LC1+0x8>)
  1e:   4478            addcc   r0, pc
  20:   4284            cmpcc   r4, r0
  22:   f044 0401       orrcc.w r4, r4, #1
  26:   bf28            it      cs
  28:   f000 f9aa       blcs    380 <cache_on>

however after applying a fix similar to yours, we do end-up with the
expected data embedded within the code and given brcmstb.S would be
subject to the same issue as tegra.S, it would not hurt.
-- 
Florian