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

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Date:   Sun, 11 Mar 2018 17:08:24 -0500
From:   Nick French <naf@...edu>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        "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 Sun, Mar 11, 2018 at 01:19:03PM -0700, Andy Lutomirski wrote:
> From memory, I see two potentially reasonable real fixes. One is to find a way to punch a hole in an ioremap.
> So you’d find the framebuffer, remove it from theproblematic mapping, and then make a new mapping. 
> The second is to change the mapping type in place. 

For the changing-in-place method, is there already an exported API that exposes change_page_attr_set without first
calling reserve_memtype? I can't seem to find one.

> Or maybe you could just iounmap the whole thing after firmware is loaded and the framebuffer is found and then
> redo the mapping right. 

I guess this would require a lock so that the ivtv-driver proper wasn't accessing the decoder's mapped memory 
during ivtvfb's iounmap-ioremap window. And a way to notify ivtv-driver proper if things go wrong? I think this method
would be very awkward because its not even memory owned by ivtvfb itself.

- Nick