Revision 6af8ae321a801a4e20183454c65eb0d23069d8ac authored by Phil Elwell on 28 January 2021, 11:30:04 UTC, committed by Phil Elwell on 28 January 2021, 11:46:41 UTC
A relatively recent commit ([1]) contained optimisation for the PIO SPI FIFO-filling functions. The commit message includes the phrase "[t]he blind and counted loops are always called with nonzero count". This is technically true, but it is still possible for count to become zero before the loop is entered - if tfr->len is zero. Moving the loop exit condition to the end of the loop saves a few cycles, but results in a near-infinite loop should the revised count be zero on entry. Strangely, zero-lengthed transfers aren't filtered by the SPI framework and, even more strangely, the Python3 spidev library is triggering them for no obvious reason. Avoid the problem completely by bailing out of the main transfer function early if trf->len is zero, although there may be a case for moving the mitigation into the framework. See: https://github.com/raspberrypi/linux/issues/4100 Signed-off-by: Phil Elwell <phil@raspberrypi.com> [1] 26751de25d25 ("spi: bcm2835: Micro-optimise FIFO loops")
1 parent c5f51df
File | Mode | Size |
---|---|---|
include | ||
Kconfig | -rw-r--r-- | 3.7 KB |
Makefile | -rw-r--r-- | 310 bytes |
counter_32k.c | -rw-r--r-- | 3.3 KB |
debug-leds.c | -rw-r--r-- | 3.6 KB |
dma.c | -rw-r--r-- | 22.6 KB |
sram.c | -rw-r--r-- | 2.8 KB |
Computing file changes ...