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

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Message-ID: <604dd2ea-d813-fa3f-3e2f-4d66175162b3@gmail.com>
Date:   Tue, 15 Dec 2020 21:56:51 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Florian Fainelli <f.fainelli@...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

15.12.2020 21:22, Florian Fainelli пишет:
> 
> 
> 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.

The VFP fix was applied to the -next very recently, it should propagate
to v5.10 eventually.

> 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?

No, start/end are printed for both THUMB2 and ARM kernels here.

> 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.
> 

Have you checked whether start/end printed after applying the fix?