Driver for SPI-based 8250 serial port

[Arnout Vandecappelle <arnout@mind.be>]

[Please CC me, I'm not on the list]

  Hi,

  I need a driver for the Exar's XR20M1280 SPI-based serial port.  It's a
16C950 compatible serial port, it just performs the register accesses over
an SPI (or I2C) bus rather than memory-mapped.

  As far as I can determine, no driver for such a device exists yet.  So I'll
develop one.

  A few questions before I start:

- I guess I should preferably write it as generically as possible, even though
I can test it on only one device?

- Should I add a UPIO_SPI to the global I/O types, or should I override the
serial_in/serial_out functions in struct plat_serial8250_port?

- I guess there should be a 8250_spi file that registers the platform
device?

- I guess it doesn't make sense to try autoconfig_irq for such a device?
The IRQ is typically a gpio which the platform code has to configure as an IRQ.

- I'm not sure how to set the uartclk. The XR20M1280's BRG is derived from a
24MHz clock, but other devices or other boards may have different values.
Should it be part of platform data?  Should I define a new platform data struct
for that?

  Any other suggestions are also welcome.

  Regards,
  Arnout

-- 
Arnout Vandecappelle                               arnout at mind be
Senior Embedded Software Architect                 +32-16-286540
Essensium/Mind                                     http://www.mind.be
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