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Subject: Re: [PATCH 4/6] media: aspeed: Support aspeed mode to reduce
 compressed data
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To: Paul Menzel <pmenzel@molgen.mpg.de>
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From: Jammy Huang <jammy_huang@aspeedtech.com>
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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