10.0-release proposed patch for Atmel

[Warner Losh]

Gentlemen,

Right now, the mountroot prompt doesn't work on Atmel CPUs. Almost all the characters are eaten. I recently committed an elegant fix for this into head to mask the interrupt for new characters and only do polling.

However, it touched the base uart. In an abundance of caution, the re@ has asked me to see if I can come up with a fix w/o that.

A less elegant, less functional fix can be found at http://people.freebsd.org/~imp/at91-mountroot-10.diff

This fix defers turning on the RXRDY bit in the interrupt mask until we get the first interrupt after the first opening of the device. This is sufficient for mountroot> to work, but wouldn't fix things like GELI that prompt the user from the kernel. I think that's acceptable for 10.0 given the typical use case for atmel.

Can the folks here that know Atmel take a look at the patch and let me know what you think?

Warner