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dm: Add pcmcia design document

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Signed-off-by: Viktor Krivak <viktor.krivak@gmail.com>
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Viktor Krivak 2012-08-08 01:42:28 +00:00 committed by Wolfgang Denk
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doc/driver-model/UDM-pcmcia.txt Normal file
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The U-Boot Driver Model Project
===============================
PCMCIA analysis
===============
Viktor Krivak <viktor.krivak@gmail.com>
2012-03-17
I) Overview
-----------
U-boot implements only 2 methods to interoperate with pcmcia. One to turn
device on and other to turn device off. Names of these methods are usually
pcmcia_on() and pcmcia_off() without any parameters. Some files in driver
directory implements only internal API. These methods aren't used outside
driver directory and they are not converted to new driver model.
II) Approach
-----------
1) New API
----------
Current API is preserved and all internal methods are hiden.
struct ops {
void (*pcmcia_on)(struct instance *i);
void (*pcmcia_off)(struct instance *i);
}
2) Conversion
-------------
In header file pcmcia.h are some other variables which are used for
additional configuration. But all have to be moved to platform data or to
specific driver implementation.
3) Platform data
----------------
Many boards have custom implementation of internal API. Pointers to these
methods are stored in platform_data. But the most implementations for Intel
82365 and compatible PC Card controllers and Yenta-compatible
PCI-to-CardBus controllers implement whole API per board. In these cases
pcmcia_on() and pcmcia_off() behave only as wrappers and call specific
board methods.
III) Analysis of in-tree drivers
--------------------------------
1) i82365.c
-----------
Driver methods have different name i82365_init() and i82365_exit but
all functionality is the same. Board files board/atc/ti113x.c and
board/cpc45/pd67290.c use their own implementation of these method.
In this case all methods in driver behave only as wrappers.
2) marubun_pcmcia.c
-------------------
Meets standard API behaviour. Simple conversion.
3) mpc8xx_pcmcia.c
------------------
Meets standard API behaviour. Simple conversion.
4) rpx_pcmcia.c
---------------
Implements only internal API used in other drivers. Non of methods
implemented here are used outside driver model.
5) ti_pci1410a.c
----------------
Has different API but methods in this file are never called. Probably
dead code.
6)tqm8xx_pcmcia.c
-----------------
Implements only internal API used in other drivers. Non of methods
implemented here are used outside driver model.