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Everytime a dead driver is removed from the list, we must re-number. This is a painful task. Try git showe53232250-- doc/driver-model/UDM-serial.txt git show6f62f4207-- doc/driver-model/UDM-serial.txt git showb9f4bc34a-- doc/driver-model/UDM-serial.txt to see what I mean. Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
74 lines
2.8 KiB
Text
74 lines
2.8 KiB
Text
The U-Boot Driver Model Project
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===============================
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Video output analysis
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=====================
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Marek Vasut <marek.vasut@gmail.com>
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2012-02-20
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I) Overview
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-----------
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The video drivers are most often registered with video subsystem. This subsystem
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often expects to be allowed access to framebuffer of certain parameters. This
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subsystem also provides calls for STDIO subsystem to allow it to output
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characters on the screen. For this part, see [ UDM-stdio.txt ].
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Therefore the API has two parts, the video driver part and the part where the
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video driver core registers with STDIO API.
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The video driver part will follow the current cfb_console approach, though
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allowing it to be more dynamic.
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II) Approach
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------------
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Registering the video driver into the video driver core is done by calling the
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following function from the driver probe() function:
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video_device_register(struct instance *i, GraphicDevice *gd);
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Because the video driver core is in charge or rendering characters as well as
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bitmaps on the screen, it will in turn call stdio_device_register(i, so), where
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"i" is the same instance as the video driver's one. But "so" will be special
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static struct stdio_device_ops handling the character output.
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III) Analysis of in-tree drivers
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--------------------------------
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arch/powerpc/cpu/mpc8xx/video.c
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-------------------------------
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This driver copies the cfb_console [ see drivers/video/cfb_console.c ]
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approach and acts only as a STDIO device. Therefore there are currently two
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possible approaches, first being the conversion of this driver to usual STDIO
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device and second, long-term one, being conversion of this driver to video
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driver that provides console.
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arch/x86/lib/video.c
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--------------------
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This driver registers two separate STDIO devices and should be therefore
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converted as such.
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board/bf527-ezkit/video.c
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-------------------------
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This driver seems bogus as it behaves as STDIO device, but provides no input
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or output capabilities. It relies on DEV_EXT_VIDEO, which is no longer in use
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or present otherwise than as a dead code/define.
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board/bf533-stamp/video.c
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-------------------------
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This driver seems bogus as it behaves as STDIO device, but provides no input
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or output capabilities. It relies on DEV_EXT_VIDEO, which is no longer in use
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or present otherwise than as a dead code/define.
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board/bf548-ezkit/video.c
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-------------------------
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This driver seems bogus as it behaves as STDIO device, but provides no input
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or output capabilities. It relies on DEV_EXT_VIDEO, which is no longer in use
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or present otherwise than as a dead code/define.
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board/cm-bf548/video.c
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----------------------
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This driver seems bogus as it behaves as STDIO device, but provides no input
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or output capabilities. It relies on DEV_EXT_VIDEO, which is no longer in use
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or present otherwise than as a dead code/define.
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