On Mon, Jun 26, 2006 at 10:07:47PM +0200, Ingo van Lil wrote:
> Correct me if I'm mistaken, but I see two possible race conditions with
> that piece of code:
>
> 1. What if the IIR actually equals UART_IIR_THRI at that point? The
> read access will clear the interrupt condition and the workaround
> will effect the actual opposite of its intention: Neither
> serial8250_start_tx() nor the interrupt handler will start
> transmitting characters for the ring buffer.
Gah, looks like you're right - reading the IIR will clear the transmit
pending interrupt, so we should probably just load the transmitter up
with characters anyway if the TEMT bit is set.
> 2. What if an interrupt is triggered shortly after reading the IIR?
> Both serial8250_start_tx() and the interrupt handler will start
> a transmission simultaneously.
This function is run under the port spinlock, so the interrupt handler
will be held off until it completes.
--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of: 2.6 Serial core
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