linux-kernel - Re: [PATCH v4 1/4] video: fbdev: atyfb: only use ioremap

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Date:   Wed, 8 Mar 2023 22:49:47 +0100
From:   Helge Deller <deller@....de>
To:     Arnd Bergmann <arnd@...db.de>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Baoquan He <bhe@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Linux-Arch <linux-arch@...r.kernel.org>, linux-mm@...ck.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Christoph Hellwig <hch@...radead.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v4 1/4] video: fbdev: atyfb: only use ioremap_uc() on i386
 and ia64

On 3/8/23 22:34, Arnd Bergmann wrote:
> 0On Wed, Mar 8, 2023, at 21:01, Luis Chamberlain wrote:
>> On Wed, Mar 08, 2023 at 09:07:07PM +0800, Baoquan He wrote:
>>> From: Arnd Bergmann <arnd@...db.de>
>>>
>>> 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.
>>>
>>> Change the only driver that still references ioremap_uc() to only do so
>>> on x86-32/ia64 in order to allow removing that interface at some
>>> point in the future for the other architectures.
>>>
>>> On some architectures, ioremap_uc() just returns NULL, changing
>>> the driver to call ioremap() means that they now have a chance
>>> of working correctly.
>>>
>>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>>> Signed-off-by: Baoquan He <bhe@...hat.com>
>>> Cc: Helge Deller <deller@....de>
>>> Cc: Thomas Zimmermann <tzimmermann@...e.de>
>>> Cc: Christophe Leroy <christophe.leroy@...roup.eu>
>>> Cc: linux-fbdev@...r.kernel.org
>>> Cc: dri-devel@...ts.freedesktop.org
>>
>> Reviewed-by: Luis Chamberlain <mcgrof@...nel.org>
>>
>> Is anyone using this driver these days? How often do fbdev drivers get
>> audited to see what can be nuked?
>
> Geert already mentioned that this one is likely used on old
> powermac systems.

and the latest generation of parisc machines use it too.

In addition, on parisc machines it's also important to map all io-space
memory uncacheable. Since ioremap() takes care of it anyway, the ioremap_uc()
was simply referencing the call to ioremap().

Helge

> I think my arm boardfile removal orphaned
> some other fbdev drivers though. I removed the ones that can
> no longer be enabled, but think a bunch of other ones
> are still selectable but have no platform_device definition
> or DT support: FB_PXA168, FB_DA8XX, FB_MX3, and MMP_FB.
>
> These four platforms are all still supported with DT, but
> over time it gets less likely that anyone is still interested
> in adding DT support to the fbdev drivers.
>
>      Arnd