linux-kernel - Re: [PATCH v7 09/10] um: Add dummy implementation for IO memcpy/memset

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Message-ID: <54985915-be13-46ee-ad42-7dd5d9d245ac@kalrayinc.com>
Date: Mon, 7 Oct 2024 09:49:00 +0200
From: Julian Vetter <jvetter@...rayinc.com>
To: Johannes Berg <johannes@...solutions.net>, Arnd Bergmann
 <arnd@...db.de>, Russell King <linux@...linux.org.uk>, Catalin Marinas
 <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Guo Ren
 <guoren@...nel.org>, Huacai Chen <chenhuacai@...nel.org>, WANG Xuerui
 <kernel@...0n.name>, Andrew Morton <akpm@...ux-foundation.org>, Geert
 Uytterhoeven <geert@...ux-m68k.org>, Richard Henderson
 <richard.henderson@...aro.org>, Ivan Kokshaysky <ink@...assic.park.msu.ru>,
 Matt Turner <mattst88@...il.com>, "James E . J . Bottomley"
 <James.Bottomley@...senpartnership.com>, Helge Deller <deller@....de>,
 Yoshinori Sato <ysato@...rs.sourceforge.jp>, Rich Felker <dalias@...c.org>,
 John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>, Richard Weinberger
 <richard@....at>, Anton Ivanov <anton.ivanov@...bridgegreys.com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-csky@...r.kernel.org, loongarch@...ts.linux.dev,
 linux-m68k@...ts.linux-m68k.org, linux-alpha@...r.kernel.org,
 linux-parisc@...r.kernel.org, linux-sh@...r.kernel.org,
 linux-um@...ts.infradead.org, linux-arch@...r.kernel.org, Yann Sionneau
 <ysionneau@...rayinc.com>
Subject: Re: [PATCH v7 09/10] um: Add dummy implementation for IO
 memcpy/memset

On 10/1/24 14:53, Johannes Berg wrote:
> On Mon, 2024-09-30 at 15:23 +0200, Julian Vetter wrote:
>> The um arch is the only architecture that sets the config 'NO_IOMEM',
>> yet drivers that use IO memory can be selected. In order to make these
>> drivers happy we add a dummy implementation for memcpy_{from,to}io and
>> memset_io functions.
> 
> Maybe I'm just not understanding this series, but how does this work
> with lib/logic_iomem.c?
> 
No, I think you're understanding the series correctly. It doesn't work. 
I will revert this.

> You're adding these inlines unconditionally, so if this included
> logic_io.h, you should get symbol conflicts?
> 
> Also not sure these functions should/need to do anything at all, there's
> no IO memory on ARCH=um in case of not having logic_io.h. Maybe even
> BUG_ON() or something? It can't be reachable (under correct drivers)
> since ioremap() always returns NULL (without logic_iomem).
> 
Thanks. You're right. I added this patch because there was a build robot 
on some mailinglist building a random config with 'ARCH=um' and with 
some MTD drivers that actually use memcpy_fromio or memcpy_toio. These 
drivers are not guarded by a 'depends on HAS_IOMEM'. I thought I could 
simply fix it by adding stub functions to the um arch. Because I saw 
there are A LOT of drivers that use IO functions without being guarded 
by 'depends on HAS_IOMEM'. Not sure though, how to handle this case.

> I think Arnd also said that other architectures might want to use
> logic_iomem, though I don't see any now.
> 
> johannes
> 
> 
> 
>