Re: [PATCH v10 3/5] media: Documentation: aspeed-video: Add user documentation for the aspeed-video driver

From: Jammy Huang
Date: Wed Oct 26 2022 - 22:13:40 EST


On 2022/10/27 上午 03:02, Nicolas Dufresne wrote:
Le mercredi 26 octobre 2022 à 10:42 +0800, Jammy Huang a écrit :
Hi Nicolas,

Thanks for your comments.

On 2022/10/25 下午 09:18, Nicolas Dufresne wrote:
Hi Jammy,

thanks for the addition.

Le mardi 25 octobre 2022 à 17:02 +0800, Jammy Huang a écrit :
Add user documentation for the aspeed-video driver.

Signed-off-by: Jammy Huang <jammy_huang@xxxxxxxxxxxxxx>
---
v10:
- new
---
.../media/drivers/aspeed-video.rst | 61 +++++++++++++++++++
.../userspace-api/media/drivers/index.rst | 1 +
2 files changed, 62 insertions(+)
create mode 100644 Documentation/userspace-api/media/drivers/aspeed-video.rst

diff --git a/Documentation/userspace-api/media/drivers/aspeed-video.rst b/Documentation/userspace-api/media/drivers/aspeed-video.rst
new file mode 100644
index 000000000000..798a2588b175
--- /dev/null
+++ b/Documentation/userspace-api/media/drivers/aspeed-video.rst
@@ -0,0 +1,61 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+.. include:: <isonum.txt>
+
+ASPEED video driver
+===================
+
+ASPEED Video Engine found on AST2400/2500/2600 SoC supports high performance
+video compressions with a wide range of video quality and compression ratio
+options. The adopted compressing algorithm is a modified JPEG algorithm.
+
+There are 2 types of compressions in this IP.
+
+* JPEG JFIF standard mode: for single frame and management compression
+* ASPEED proprietary mode: for multi-frame and differential compression.
+ Support 2-pass (high quality) video compression scheme (Patent pending by
+ ASPEED). Provide visually lossless video compression quality or to reduce
+ the network average loading under intranet KVM applications.
I think some of the information disclosed in the following quote could be
summarized. Notably the part about the extra buffers.

Aspeed JPEG Format requires an additional buffer, called bcd, to store
the information about which macro block in the new frame is different
from the previous 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.
But before I push you this route, have you considered using a dedicated pixel
format instead ? Here's my thinking, the output of the JPEG encoder is no longer
"compatible" (or at least won't yield the expected images) if used with a normal
JPEG decoder. By differentiating these two as dedicated formats, you will only need
1 vendor control, and you avoid the potential risk of software bugs mixing them up.
Also note that there is other JPEG based vendor formats that exist in V4L2.

Let me know what do you think ?
Yes, I also add a dedicated formats, V4L2_PIX_FMT_AJPG, in this series.
In [PATCH v10 1/5]

media: v4l: Add definition for the Aspeed JPEG format, I add the
description in pixfmt-reserved.rst.

After this series applied, the users can choose either of these two
formats by VIDIOC_S_FMT as

per their preference.
Sorry about that, I have skipped too much. The approach seems fair then, can you
state in the doc that these control applies to V4L2_PIX_FMT_AJPG in some way ?
(just a little cross-reference can help). The confusion with normal JPEG is
easy.

thanks for you patience,
Nicolas

Sure, I will add the words below in next patch.

"VIDIOC_S_FMT can be used to choose which format you want. V4L2_PIX_FMT_JPEG

stands for JPEG JFIF standard mode; V4L2_PIX_FMT_AJPG stands for ASPEED

proprietary mode."


Thanks for your help.

Nicolas

+
+More details on the ASPEED video hardware operations can be found in
+*chapter 6.2.16 KVM Video Driver* of SDK_User_Guide which available on
+AspeedTech-BMC/openbmc/releases.
+
+The ASPEED video driver implements the following driver-specific control:
+
+``V4L2_CID_ASPEED_HQ_MODE``
+-------------------------------
+ Enable/Disable ASPEED's High quality mode. This is a private control
+ that can be used to enable high quality for aspeed proprietary mode.
+
+.. flat-table::
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 1 4
+
+ * - ``(0)``
+ - ASPEED HQ mode is disabled.
+ * - ``(1)``
+ - ASPEED HQ mode is enabled.
+
+``V4L2_CID_ASPEED_HQ_JPEG_QUALITY``
+-------------------------------
+ Define the quality of ASPEED's High quality mode. This is a private control
+ that can be used to decide compression quality if High quality mode enabled
+ . Higher the value, better the quality and bigger the size.
+
+.. flat-table::
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 1 4
+
+ * - ``(1)``
+ - minimum
+ * - ``(12)``
+ - maximum
+ * - ``(1)``
+ - step
+ * - ``(1)``
+ - default
+
+**Copyright** |copy| 2022 ASPEED Technology Inc.
diff --git a/Documentation/userspace-api/media/drivers/index.rst b/Documentation/userspace-api/media/drivers/index.rst
index 32f82aed47d9..46a494e00b72 100644
--- a/Documentation/userspace-api/media/drivers/index.rst
+++ b/Documentation/userspace-api/media/drivers/index.rst
@@ -31,6 +31,7 @@ For more details see the file COPYING in the source distribution of Linux.
:maxdepth: 5
:numbered:
+ aspeed-video
ccs
cx2341x-uapi
dw100

--
Best Regards
Jammy