linux-kernel - Re: [3.8-rc4 arm] SCSI_SYM53C8XX

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Date:	Tue, 22 Jan 2013 11:03:04 +0100
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:	rob.herring@...xeda.com, grant.likely@...retlab.ca,
	rmk+kernel@....linux.org.uk, linux-kernel@...r.kernel.org
Subject: Re: [3.8-rc4 arm] SCSI_SYM53C8XX_2 module cannot register IRQ

On Tue, Jan 22, 2013 at 10:17 AM, Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:

>> 1.  Get hold of the patch fixing the boot regression:
>>     git format-patch
>> f5565295892eb93c3191aa241405fe8b685542d6^..f5565295892eb93c3191aa241405fe8b685542d6
>
> Thanks, but sorry, I couldn't understand how this command line works.
>
> Which one ("blank console bug" or "IRQ registration failure bug") does
> "the boot regression" refer?

They are likely one and the same bug? The only regression on
the versatile I have caused came from commit
f5565295892eb93c3191aa241405fe8b685542d6.

> Your command line generated only one patch but you say "iterate".

I mean you should iterate the process, not the patch generation.

>   $ git format-patch f5565295^..f5565295
>   0001-ARM-7610-1-versatile-bump-IRQ-numbers.patch
>
> If I use 5c49985c^..5c49985c (the patch which the blank console bug was fixed),
> it generated 8 patches.

This is because you have made git format-patch in a merge commit
which contains several patches.

You can probably actually apply all of them at each step like
that if  you prefer: patch -p1 < *.patch

> Since the IRQ registration failure bug message contains IRQ number "27",
> I suspect f5565295 "ARM: 7610/1: versatile: bump IRQ numbers"

Me too :-) Atleast Grant told me that that one patch fixed the
boot regression.

And that is why I mentioned that patch specifically above,
I think it's the only one you need.

> and 5ced33bc06 "ARM: 7611/1: VIC: fix bug in VIC irqdomain code"

I don't think you need this patch.

> but how can I test them?

Apply/compile/boot?

Sorry I don't quite get the question?

>> 2. At each iterative step using git bisect:
>>    patch -p1 < 0001-ARM-7610-1-versatile-bump-IRQ-numbers.patch
>>
>> 3. Boot/trial-and-horror
>>
>> 4. git reset --hard HEAD
>>    To nullify the effects of the patch.
>>
>> 5. git bisect [good|bad]
>>
> Excuse me, what range do I need to pass to "git bisect start" command line?

Same as you mentioned in your first mail I suppose?

>> 6. Iterate from (2) until you find the bug.

When you cannot proceed because you need a patch unrelated to the
problem you want to solve, you apply that patch on top of the
bisection HEAD with patch -p1 < foo.patch, test, reset HEAD,
git bisect <result> etc....

I'm sorry if this is a bit complicated but bisection down several
regressions is one of the more advanced forms of regression
bug hunt... You're quite cool if you can handle it :-)

Yours,
Linus Walleij
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