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Subject: Re: [PATCH] sh: Avoid using IRQ0 on SH3 and SH4
To:     John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
        Guenter Roeck <linux@roeck-us.net>
CC:     Yoshinori Sato <ysato@users.sourceforge.jp>,
        Rich Felker <dalias@libc.org>, <linux-sh@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
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 <544f02b696a0a1554efe63f799754f3e5fbfecdc.camel@physik.fu-berlin.de>
From:   Sergey Shtylyov <s.shtylyov@omp.ru>
Organization: Open Mobile Platform
Message-ID: <b75efe15-e679-2557-253a-0cc82ff8f926@omp.ru>
Date:   Sat, 8 Jul 2023 23:35:48 +0300
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On 7/6/23 5:01 PM, John Paul Adrian Glaubitz wrote:
[...]

>> On Thu, Jun 01, 2023 at 11:22:17PM +0300, Sergey Shtylyov wrote:
>>> IRQ0 is no longer returned by platform_get_irq() and its ilk -- they now
>>> return -EINVAL instead.  However, the kernel code supporting SH3/4-based
>>> SoCs still maps the IRQ #s starting at 0 -- modify that code to start the
>>> IRQ #s from 16 instead.
>>>
>>> The patch should mostly affect the AP-SH4A-3A/AP-SH4AD-0A boards as they
>>> indeed are using IRQ0 for the SMSC911x compatible Ethernet chip.
>>>
>>
>> Unfortunately it also affects all sh4 emulations in qemu, and results in
>> boot stalls with those. There isn't a relevant log to attach because there
>> is no error message - booting just stalls until the emulation is aborted.
>>
>> Reverting this patch fixes the problem.
>>
>> Bisect log is attached for reference. Note that bisect requires applying
>> commit 7497840d462c ("sh: Provide unxlate_dev_mem_ptr() in asm/io.h"),
>> which is also the reason why the problem was not observed earlier since
>> it was hiding behind a build failure.
> 
> Interesting. My naive understanding was that IRQ0 is no longer usable in the
> kernel as Sergey claimed. Was that not correct?

    According to Linus, using IRQ0 should only be allowed in the arch/ code
(usually the i8253 driver). As for the platform devices, this have been finally
enforced by this patch.

> Adrian

MBR, Sergey