linux-kernel - Re: [PATCH v8 1/6] drm/fourcc: Add modifier definitions for describing Amlogic Video Framebuffer Compression

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Message-ID: <20200702131834.GZ3278063@phenom.ffwll.local>
Date:   Thu, 2 Jul 2020 15:18:34 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Simon Ser <contact@...rsion.fr>
Cc:     Neil Armstrong <narmstrong@...libre.com>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "jianxin.pan@...ogic.com" <jianxin.pan@...ogic.com>,
        Kevin Hilman <khilman@...libre.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-amlogic@...ts.infradead.org" 
        <linux-amlogic@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v8 1/6] drm/fourcc: Add modifier definitions for
 describing Amlogic Video Framebuffer Compression

On Thu, Jul 02, 2020 at 09:23:11AM +0000, Simon Ser wrote:
> On Thursday, July 2, 2020 9:47 AM, Neil Armstrong <narmstrong@...libre.com> wrote:
> 
> > Finally is also adds the Scatter Memory layout, meaning the header contains IOMMU
> > references to the compressed frames content to optimize memory access
> > and layout.
> >
> > In this mode, only the header memory address is needed, thus the content
> > memory organization is tied to the current producer execution and cannot
> > be saved/dumped neither transferrable between Amlogic SoCs supporting this
> > modifier.
> 
> Still not sure how to handle this one, since this breaks fundamental
> assumptions about modifiers.

I wonder whether we should require special allocations for these, and then
just outright reject mmap on these buffers. mmap on dma-buf isn't a
required feature.

That would make sure that userspace cannot look at them.

Also I'm kinda suspecting that there's not unlimited amounts of this magic
invisible storage available anyway.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch