Hi, On 25/03/2020 14:49, Pekka Paalanen wrote: > On Wed, 25 Mar 2020 11:24:15 +0100 > Neil Armstrong <narmstr...@baylibre.com> wrote: > >> Hi, >> >> On 25/03/2020 10:04, Simon Ser wrote: >>> On Wednesday, March 25, 2020 9:50 AM, Neil Armstrong >>> <narmstr...@baylibre.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/ >>> >> >> I really understand your point, but this is one of the use-cases we need >> solve. >> This is why I split the fourcc patch and added an explicit comment. >> >> Please point me a way to display such buffer, the HW exists, works like that >> and >> it's a fact and can't change. >> >> It will be the same for secure zero-copy buffers we can't map from >> userspace, but >> only the HW decoder can read/write and HW display can read. > > The comparison to secure buffers is a good one. > > Are buffers with the DRM_FORMAT_MOD_AMLOGIC_FBC_LAYOUT_SCATTER modifier > meaningfully mmappable to CPU always / sometimes / never / > varies-and-cannot-know?
mmappable, yes in our WIP V4L2 driver in non-secure path, meaningful, absolutely never. So yeah, these should not be mmappable since not meaningful. > > Maybe this type should be handled similar to secure buffers, with the > exception that they are not actually secured but only mostly > inaccessible. Then again, I haven't looked at any of the secure buffer > proposals. Actually, the Amlogic platforms offers secure video path using these exact modifiers, AFAIK it doesn't support the NV12 dual-write output in secure. AFAIK last submission is from AMD, and it doesn't talk at all about mmapability of the secure BOs. Neil > > > Thanks, > pq >
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