linux-kernel - Re: ivtv: use arch_phys_wc_add() and require PAT disabled

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Date:   Thu, 8 Mar 2018 04:14:11 +0000
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Andy Lutomirski <luto@...nel.org>
Cc:     "French, Nicholas A." <naf@...edu>,
        "hans.verkuil@...co.com" <hans.verkuil@...co.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>
Subject: Re: ivtv: use arch_phys_wc_add() and require PAT disabled

On Thu, Mar 08, 2018 at 04:06:01AM +0000, Luis R. Rodriguez wrote:
> On Thu, Mar 08, 2018 at 03:16:29AM +0000, French, Nicholas A. wrote:
> > On Wed, Mar 07, 2018 at 07:02:05PM +0000, Luis R. Rodriguez wrote:
> > > On Tue, Mar 06, 2018 at 09:01:10PM +0000, French, Nicholas A. wrote:
> > > > any reason why PAT can't be enabled for ivtvfb as simply as in the attached
> > > > patch?
> > >
> > > Prior to your change the OSD buffer was obtained using the itv->dec_mem + oi->video_rbase
> > > given itv->dec_mem was initialized via [...]
> > >         itv->dec_mem = ioremap_nocache(itv->base_addr + IVTV_DECODER_OFFSET - oi->video_buffer_size,
> > >                                 IVTV_DECODER_SIZE);
> > 
> > Ah, I see. So my proposed ioremap_wc call was only "working" by aliasing the
> > ioremap_nocache()'d mem area and not actually using write combining at all.
> 
> There are some debugging PAT toys out there I think but I haven't played with
> them yet or I forgot how to to confirm or deny this sort of effort, but
> likeley.

In fact come to think of it I believe some neurons are telling me that if
two type does not match we'd get an error?

  Luis