To enable this feature just define CONFIG_HWCONFIG in your board
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config file.
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This implements a simple hwconfig infrastructure: an
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interface for software knobs to control hardware.
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This a is very simple implementation, i.e. it is implemented
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via the `hwconfig' environment variable. Later we could write
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some "hwconfig <enable|disable|list>" commands, ncurses
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interface for Award BIOS-like interface, and frame-buffer
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interface for AMI GUI[1] BIOS-like interface with mouse
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support[2].
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Current implementation details/limitations:
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1. Doesn't support options dependencies and mutual exclusion.
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We can implement this by integrating apt-get[3] into Das
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U-Boot. But I haven't bothered yet.
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2. Since we don't implement a hwconfig command, i.e. we're working
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with the environment directly, there is no way to tell that
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toggling a particular option will need a reboot to take
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effect. So, for now it's advised to always reboot the
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target after modifying the hwconfig variable.
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3. We support hwconfig options with arguments. For example,
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set hwconfig "dr_usb:mode=peripheral,phy_type=ulpi"
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This selects three hwconfig options:
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1. dr_usb - enable Dual-Role USB controller;
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2. dr_usb_mode:peripheral - USB in Function mode;
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3. dr_usb_phy_type:ulpi - USB should work with ULPI PHYs.
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The purpose of this simple implementation is to refine the
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internal API and then we can continue improving the user
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experience by adding more mature interfaces, like a hwconfig
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command with bells and whistles. Or not adding, if we feel
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that the current interface fits people's needs.
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[1] http://en.wikipedia.org/wiki/American_Megatrends
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[2] Regarding ncurses and GUI with mouse support -- I'm just
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kidding.
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[3] The comment regarding apt-get is also a joke, meaning that
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dependency tracking could be non-trivial. For example, for
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enabling HW feature X we may need to disable Y, and turn Z
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into reduced mode (like RMII-only interface for ethernet,
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no MII).
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It's quite trivial to implement simple cases though.
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