Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Sender: Guenter Roeck <groeck7@gmail.com>
Message-ID: <b02489c7-96de-b6ed-07b9-9ba423af34c6@roeck-us.net>
Date:   Wed, 12 Jul 2023 08:38:38 -0700
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.13.0
Content-Language: en-US
To:     Sergei Shtylyov <sergei.shtylyov@gmail.com>,
        David Laight <David.Laight@ACULAB.COM>,
        'John Paul Adrian Glaubitz' <glaubitz@physik.fu-berlin.de>,
        Sergey Shtylyov <s.shtylyov@omp.ru>,
        Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     Yoshinori Sato <ysato@users.sourceforge.jp>,
        Rich Felker <dalias@libc.org>,
        "linux-sh@vger.kernel.org" <linux-sh@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <fbfea3ad-d327-4ad5-ac9c-648c7ca3fe1f@roeck-us.net>
 <CAMuHMdUfXdCf_CQuWXpP72MzKFYvXg3Ud1VN_3Bd0RHxfLhVeQ@mail.gmail.com>
 <7b2c0d812280afaefee0c70a9aea00a0fcf84e3a.camel@physik.fu-berlin.de>
 <cd1caa5d-fbd8-c3fe-29e9-b848ddd5634c@omp.ru>
 <1178f8d0-be70-c088-ee6a-8b421b290624@roeck-us.net>
 <a0a0d4d06eecc9c3194afe2cee0b61ebed5e0392.camel@physik.fu-berlin.de>
 <c5ad5c59fcfa4888bd03fb8a855c989c@AcuMS.aculab.com>
 <c9483d7f-7f5f-dd29-2bba-5659a1dae7e0@gmail.com>
From:   Guenter Roeck <linux@roeck-us.net>
Subject: Re: [PATCH] sh: Avoid using IRQ0 on SH3 and SH4
In-Reply-To: <c9483d7f-7f5f-dd29-2bba-5659a1dae7e0@gmail.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 7/12/23 01:20, Sergei Shtylyov wrote:
> On 7/12/23 11:12 AM, David Laight wrote:
> 
>>> Sent: 09 July 2023 00:13
>> ....
>>> Looking at arch/sh/boards/mach-r2d/irq.c, there is some IRQ translation going
>>> on and maybe that's the part where we need to correct the offset by 16?
>>
>> Would it be less problematic to use (say) 16 for IRQ_0
>> leaving IRQ_1+ as 1+ ?
> 
>     I don't think so.
> 
>> At least that would only cause issues for code that needed
>> to use IRQ_0.
>>
>> (It has to be said that making IRQ 0 invalid seemed wrong
>> to me. x86 (IBM PC) gets away with it because IRQ 0 is
>> always assigned to platform specific hardware.)
> 
>     Not only x86, IIRC.
>     Have you seen the commit below?
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ce753ad1549cbe9ccaea4c06a1f5fa47432c8289
> 

Quoting:

using IRQ0 is considered invalid (according to Linus) outside the arch/ code
                                                       ^^^^^^^^^^^^^^^^^^^^^^

The changes here were made _in_ the arch code. While there may be valid
arguments for doing that, quoting the above commit as reason isn't really
sufficient.

Guenter