CPM_UART: tcdrain() is broken

[Laurent Pinchart]

Hi everybody,

while working with a CPM UART port (SMC2), I noticed that tcdrain() doesn't 
actually wait until all the characters hit the wire. After some 
investigation, I found out that uart_wait_until_sent() (in 
drivers/serial/serial_core.c) returns immediately because port->fifosize is 
equal to 0.

The following patch improves the situation by setting fifosize and calling 
uart_update_timeout() when the baud rate is modified. It didn't break might 
system, but further testing is probably needed.

There is, however, a problem left. The SCC controllers have a 32-byte FIFO 
between the buffer descriptors and the wires. cpm_uart_tx_empty() checks if 
all buffer descriptors have been processed, but doesn't check if the transmit 
FIFO is actually empty. I can't figure out how to do so from the datasheet. 
Does anyone have an idea ?

Best regards,

Laurent Pinchart
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