On 19.09.2016 17:26, Noralf Trønnes wrote:
Writing messages larger than the FIFO size results in a hang, rendering
the machine unusable. This is because the RXD status flag is set on the
first interrupt which results in bcm2835_drain_rxfifo() stealing bytes
from the buffer. The controller continues to trigger interrupts waiting
for the missing bytes, but bcm2835_fill_txfifo() has none to give.
I remember having seen similar interrupt issues with the SPI HW-block.
In this situation wait_for_completion_timeout() apparently is unable to
stop the madness.
That is because it is a level irq that immediately triggers another interrupt giving
no CPU no time to do other (threaded) OS activity - this might be slightly
different for multi-core machines...
The BCM2835 ARM Peripherals datasheet has this to say about the flags:
   TXD: is set when the FIFO has space for at least one byte of data.
   RXD: is set when the FIFO contains at least one byte of data.
   TXW: is set during a write transfer and the FIFO is less than full.
   RXR: is set during a read transfer and the FIFO is or more full.

Implementing the logic from the downstream i2c-bcm2708 driver solved
the hang problem.

Signed-off-by: Noralf Trønnes<nor...@tronnes.org>
Reviewed-by: Martin Sperl <ker...@martin.sperl.org>

Reply via email to