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

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Message-ID: <20180312040401.GA4814@tivo.lan>
Date:   Sun, 11 Mar 2018 23:04:02 -0500
From:   Nick French <naf@...edu>
To:     Ian Armstrong <mail01@...mst.co.uk>
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 11:24:38PM +0000, Ian Armstrong wrote:
> On Sat, 10 Mar 2018 16:57:41 +0000
> "French, Nicholas A." <naf@...edu> wrote:
> 
> > > > No what if the framebuffer driver is just requested as a
> > > > secondary step after firmware loading?  
> > >
> > > Its a possibility. The decoder firmware gets loaded at the
> > > beginning of the decoder memory range and we know its length, so
> > > its possible to ioremap_nocache enough room for the firmware only
> > > on init and then ioremap the remaining non-firmware decoder memory
> > > areas appropriately after the firmware load succeeds...  
> > 
> > I looked in more detail, and this would be "hard" due to the way the
> > rest of the decoder offsets are determined by either making firmware
> > calls or scanning the decoder memory range for magic bytes and other
> > mess.
> 
> The buffers used for yuv output are fixed. They are located both before
> and after the framebuffer. Their offset is fixed at 'base_addr +
> IVTV_DECODER_OFFSET + yuv_offset[]'. The yuv offsets can be found in
> 'ivtv-yuv.c'. The buffers are 622080 bytes in length.
> 
> The range would be from 'base_addr + 0x01000000 + 0x00029000' to
> 'base_addr + 0x01000000 + 0x00748200 + 0x97dff'. This is larger than
> required, but will catch the framebuffer and should not cause any
> problems. If you wanted to render direct to the yuv buffers, you would
> probably want this region included anyway (not that the current driver
> supports that).

Am I correct that you are talking about the possibility of re-ioremap()-ing
the 'yuv-fb-yuv' area *after* loading the firmware, not of mapping ranges
correctly on the first go-around?

Because unless my math is letting me down, the decoder firmware is already
loaded from 'base_addr + 0x01000000 + 0x0' to 'base_addr + 0x01000000 + 0x3ffff'
which overlaps the beginning of the yuv range.

- Nick