linux-kernel - Re: [PATCH v4 7/8] drm/fourcc: amlogic: Add modifier definitions for the Scatter layout

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Message-ID: <JgBZ7eZYMgXRNu_-E4ItS1bud9mEe15xptZEX_XhsM_h8_iIZTOmPokEVxPJYwX0wP0pmb5p-ymubyyZP3kVbcfuDNdmM0__L8wBR5IykfE=@emersion.fr>
Date:   Wed, 25 Mar 2020 09:04:09 +0000
From:   Simon Ser <contact@...rsion.fr>
To:     Neil Armstrong <narmstrong@...libre.com>
Cc:     "daniel@...ll.ch" <daniel@...ll.ch>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "mjourdan@...libre.com" <mjourdan@...libre.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 v4 7/8] drm/fourcc: amlogic: Add modifier definitions for the Scatter layout

On Wednesday, March 25, 2020 9:50 AM, Neil Armstrong <narmstrong@...libre.com> wrote:

> Amlogic uses a proprietary lossless image compression protocol and format
> for their hardware video codec accelerators, either video decoders or
> video input encoders.
>
> This introduces the Scatter Memory layout, means 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.

I don't think this is suitable for modifiers. User-space relies on
being able to copy a buffer from one machine to another over the
network. It would be pretty annoying for user-space to have a blacklist
of modifiers that don't work this way.

Example of such user-space:
https://gitlab.freedesktop.org/mstoeckl/waypipe/