|README on the Compact Flash for Card Engines
|There are three challenges in supporting the CF interface of the Card
|Engines. First, every IO operation must be followed with IO to
|another memory region. Second, the slot is wired for one-to-one
|address mapping *and* it is wired for 16 bit access only. Second, the
|interrupt request line from the CF device isn't wired.
|The IOBARRIER issue is covered in README.IOBARRIER. This isn't an
|onerous problem. Enough said here.
|The addressing issue is solved in the
|arch/arm/mach-lh7a40x/ide-lpd7a40x.c file with some awkward
|work-arounds. We implement a special SELECT_DRIVE routine that is
|called before the IDE driver performs its own SELECT_DRIVE. Our code
|recognizes that the SELECT register cannot be modified without also
|writing a command. It send an IDLE_IMMEDIATE command on selecting a
|drive. The function also prevents drive select to the slave drive
|since there can be only one. The awkward part is that the IDE driver,
|even though we have a select procedure, also attempts to change the
|drive by writing directly the SELECT register. This attempt is
|explicitly blocked by the OUTB function--not pretty, but effective.
|The lack of interrupts is a more serious problem. Even though the CF
|card is fast when compared to a normal IDE device, we don't know that
|the CF is really flash. A user could use one of the very small hard
|drives being shipped with a CF interface. The IDE code includes a
|check for interfaces that lack an IRQ. In these cases, submitting a
|command to the IDE controller is followed by a call to poll for
|completion. If the device isn't immediately ready, it schedules a
|timer to poll again later.