linux-kernel - Re: [PATCH] video: fbdev: atyfb: only use ioremap

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Message-ID: <20191113184505.GW11244@42.do-not-panic.com>
Date:   Wed, 13 Nov 2019 18:45:05 +0000
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Christoph Hellwig <hch@....de>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Juergen Gross <jgross@...e.com>,
        Tuowen Zhao <ztuowen@...il.com>,
        AceLan Kao <acelan.kao@...onical.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Roman Gilg <subdiff@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        "Luis R. Rodriguez" <mcgrof@...e.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        X86 ML <x86@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, linux-ia64@...r.kernel.org,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Souptick Joarder <jrdr.linux@...il.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] video: fbdev: atyfb: only use ioremap_uc() on i386 and
 ia64

On Wed, Nov 13, 2019 at 11:31:54AM +0200, Andy Shevchenko wrote:
> On Wed, Nov 13, 2019 at 08:38:15AM +0100, Arnd Bergmann wrote:
> > On Wed, Nov 13, 2019 at 8:27 AM Christoph Hellwig <hch@....de> wrote:
> > >
> > > On Tue, Nov 12, 2019 at 10:24:23PM +0000, Luis Chamberlain wrote:
> > > > I think this would be possible if we could flop ioremap_nocache() to UC
> > > > instead of UC- on x86. Otherwise, I can't see how we can remove this by
> > > > still not allowing direct MTRR calls.
> > >
> > > If everything goes well ioremap_nocache will be gone as of 5.5.
> > 
> > As ioremap_nocache() just an alias for ioremap(), I suppose the idea would
> > then be to make x86 ioremap be UC instead of UC-, again matching what the
> > other architectures do already.
> 
> I think it's right thing to do, i.e. assume that ioremap() always does strong
> UC independently on MTRR settings.

Agreed wholeheartedly. What are the blockers from making that happen? Do
we have any left?

  Luis