Re: [PATCH 4/6] media: aspeed: Support aspeed mode to reduce compressed data

[Jammy Huang]

Dear Paul,

Thanks for your help.

On 2021/10/18 下午 05:34, Paul Menzel wrote:
> Dear Jammy,
>
>
> Am 18.10.21 um 10:51 schrieb Jammy Huang:
>
> > On 2021/10/14 下午 02:47, Paul Menzel wrote:
> > > Am 14.10.21 um 05:48 schrieb Jammy Huang:
> > > > aspeed support differential jpeg format which only compress the parts
> > > support*s*
> > >
> > > > which are changed. In this way, it reduces both the amount of data to be
> > > > transferred by network and those to be decoded on the client side.
> > > Please mention the datasheet name and revision and section, where this
> > > functionality is described.
> > Sorry but our datasheet is confidential. The basic idea of this
> > feature is that we can just compress the blocks which is different
> > with previous frame rather than full frame. This idea is similar to
> > the I & P frame in multimedia.
> It’s still good to have the name and revision of the datasheet, the code
> was developed against documented. (Public datasheets would be even
> better, also for review.)
You can reference to the datasheet of ast2600 revision 9 at section 36, 
Video Engine.

> > > Which chips support it?
> > AST2400/2500/2600 all support it.
> > > > 4 new ctrls are added:
> > > > *Aspeed JPEG Format: to control aspeed's partial jpeg on/off
> > > > *Aspeed Compression Mode: to control aspeed's compression mode
> > > > *Aspeed HQ Mode: to control aspeed's HQ mode on/off
> > > > *Aspeed HQ Quality: to control the quality of aspeed's HQ mode
> > > Please add a space after the bullet points.
> > >
> > > Excuse my ignorance, how can these options be controlled?
> > * Aspeed JPEG Format: to control jpeg format
> >     0: standard jpeg, 1: aspeed jpeg
> > * Aspeed Compression Mode: to control aspeed's compression mode
> >     0: DCT Only, 1: DCT VQ mix 2-color, 2: DCT VQ mix 4-color
> >     This is AST2400 only. It will adapt JPEG or VQ encoding method according
> >     to the context automatically.
> > * Aspeed HQ Mode: to control aspeed's HQ mode on/off
> >     0: disabled, 1: enabled
> > * Aspeed HQ Quality: to control the quality(0~11) of aspeed's HQ mode,
> >     only usefull if Aspeed HQ mode is enabled
> Thank you. So some sysfs file?
This is a v4l2 based driver, so I prefer to use v4l2 control interface 
rather than sysfs.
The user can iterate v4l2 control by V4L2_CTRL_FLAG_NEXT_CTRL to know 
what is
available. For example, the following is the information that 
aspeed_video driver supports

[User Controls                 ]
Aspeed JPEG Format             : type=1, minimum=0, maximum=2, step=1, 
default_value=0
Aspeed Compression Mode        : type=1, minimum=0, maximum=2, step=1, 
default_value=0
Aspeed HQ Mode                 : type=2, minimum=0, maximum=1, step=1, 
default_value=0
Aspeed HQ Quality              : type=1, minimum=0, maximum=11, step=1, 
default_value=0
[JPEG Compression Controls     ]
Chroma Subsampling             : type=3, minimum=0, maximum=2, step=1, 
default_value=0
Compression Quality            : type=1, minimum=0, maximum=11, step=1, 
default_value=0

> > > > Aspeed JPEG Format requires an additional buffer, called bcd, to store
> > > > the information that which macro block in the new frame is different
> > > s/that which/which/
> > >
> > > > from the old one.
> > > >
> > > > To have bcd correctly working, we need to swap the buffers for src0/1 to
> > > > make src1 refer to previous frame and src0 to the coming new frame.
> > > How did you test it? What do the clients need to support?
> > >
> > > Did you test, how much bandwidth is saved? Some numbers would be nice.
> > I tested it by aspeed's kvm client which support decoding the aspeed
> > format. Currently, I am porting this feature to novnc to have openbmc
> > support it.
> Nice.
> > The bandwidth saved is variant. It depends on how many blocks is
> > different between new and old frame.If the new frame is identical
> > with the previous one, the compressed frame only needs 12 Bytes.
> Thank you for the explanation.
>
>
> Kind regards,
>
> Paul