Hi!
On Tue, Apr 11, 2023 at 11:52:20AM -0400, William Breathitt Gray wrote:
commit 4aa3b75c74603c3374877d5fd18ad9cc3a9a62ed upstream.
The Counter (CNTR) register is 24 bits wide, but we can have an effective 25-bit count value by setting bit 24 to the XOR of the Borrow flag and Carry flag. The flags can be read from the FLAG register, but a race condition exists: the Borrow flag and Carry flag are instantaneous and could change by the time the count value is read from the CNTR register.
Since the race condition could result in an incorrect 25-bit count value, remove support for 25-bit count values from this driver.
I believe usual solution is to read the carry, read the counter, and read the carry again. If old_carry = new_carry, we are pretty sure we did not hit the race, and can use 25 bit value.
Best regards, Pavel