linux-kernel - Re: [PATCH v3 2/2] arch/*/io.h: remove ioremap

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Message-ID: <87sfej1rie.fsf@mpe.ellerman.id.au>
Date:   Sun, 05 Mar 2023 20:23:05 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Baoquan He <bhe@...hat.com>, linux-kernel@...r.kernel.org
Cc:     linux-arch@...r.kernel.org, linux-mm@...ck.org, arnd@...db.de,
        geert@...ux-m68k.org, mcgrof@...nel.org, hch@...radead.org,
        Baoquan He <bhe@...hat.com>, linux-alpha@...r.kernel.org,
        linux-hexagon@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
        linux-mips@...r.kernel.org, linux-parisc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-sh@...r.kernel.org,
        sparclinux@...r.kernel.org
Subject: Re: [PATCH v3 2/2] arch/*/io.h: remove ioremap_uc in some
 architectures

Baoquan He <bhe@...hat.com> writes:
> ioremap_uc() is only meaningful on old x86-32 systems with the PAT
> extension, and on ia64 with its slightly unconventional ioremap()
> behavior, everywhere else this is the same as ioremap() anyway.
>
> Here, remove the ioremap_uc() definition in architecutures other
> than x86 and ia64. These architectures all have asm-generic/io.h
> included and will have the default ioremap_uc() definition which
> returns NULL.
>
> Note: This changes the existing behaviour and could break code
> calling ioremap_uc(). If any ARCH meets this breakage and really
> needs a specific ioremap_uc() for its own usage, one ioremap_uc()
> can be added in the ARCH.

I see one use in:

drivers/video/fbdev/aty/atyfb_base.c:        par->ati_regbase = ioremap_uc(info->fix.mmio_start, 0x1000);


Which isn't obviously x86/ia64 specific.

I'm pretty sure some powermacs (powerpc) use that driver.

Maybe that exact code path is only reachable on x86/ia64? But if so
please explain why.

Otherwise it looks like this series could break that driver on powerpc
at least.

cheers