spi: dw: Fix detecting FIFO depth
commit d297933c upstream. Current code tries to find the highest valid fifo depth by checking the value it wrote to DW_SPI_TXFLTR. There are a few problems in current code: 1) There is an off-by-one in dws->fifo_len setting because it assumes the latest register write fails so the latest valid value should be fifo - 1. 2) We know the depth could be from 2 to 256 from HW spec, so it is not necessary to test fifo == 257. In the case fifo is 257, it means the latest valid setting is fifo = 256. So after the for loop iteration, we should check fifo == 2 case instead of fifo == 257 if detecting the FIFO depth fails. This patch fixes above issues. Signed-off-by: Axel Lin <axel.lin@ingics.com> Reviewed-and-tested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Signed-off-by: Mark Brown <broonie@kernel.org> [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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