Hi everybody, I'm implementing flow control and modem control lines support in the cpm_uart driver.
The implementation is based on the GPIO lib. Modem control lines are described in the device tree as GPIO resources and accessed through the OF GPIO bindings. The I/O ports have to be initialized as GPIOs in the platform-specific code. Reading and writing the modem control lines isn't an issue, but activating hardware flow control is more complex. The driver needs to turn dedicated functions on and off for the RTS and CTS signals, and the GPIO API doesn't provide a way to access the PPAR* registers (which does make sense - although arguably - as PPAR* control specific functions, not GPIOs). Hardcoding RTS and CTS lines control in the driver is not an option I want to consider. Extending the GPIO API to handled special functions has been nacked in the past (see http://ozlabs.org/pipermail/linuxppc-dev/2008-February/051241.html). An option would be to export gpio_to_chip from drivers/gpio/gpiolib.c and use cpm1/2_set_pin in the cpm_uart driver. Can anyone think of a better solution ? Best regards, -- Laurent Pinchart CSE Semaphore Belgium Chaussee de Bruxelles, 732A B-1410 Waterloo Belgium T +32 (2) 387 42 59 F +32 (2) 387 42 75
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