From f296c9452269ca22143004aa74f70e66288d4ddd Mon Sep 17 00:00:00 2001 From: Gabe Black Date: Mon, 7 Apr 2014 01:01:56 -0700 Subject: tegra: spi: Read the command1 register to ensure the write to it completes. To ensure that the command1 write which sets the "go" bit completes before other reads to the device. Otherwise, there's a race condition where those register values might still have their values from the last transfer. With different SPI clock frequencies, that could lead to spi_delay being told there were negative bytes still to send. Its expected delay would wrap to a negative value, that was passed to udelay, and the system would sit there for 4 seconds not doing anything. BUG=None TEST=Built and booted on nyan. Set the SPI bus frequency to a value which was causing the 4+ second delay and verified that it no longer happened. BRANCH=None Original-Change-Id: I8b4090efc69f34d0413e3f63c59c1825dd151cec Original-Signed-off-by: Gabe Black Original-Reviewed-on: https://chromium-review.googlesource.com/193347 Original-Reviewed-by: Gabe Black Original-Commit-Queue: Gabe Black Original-Tested-by: Gabe Black (cherry picked from commit d7ea9febdf2c5942f81607ee6ded786c9a8954bb) Signed-off-by: Marc Jones Change-Id: I095bfc745eda37b8e666475ceb41684152f3709a Reviewed-on: http://review.coreboot.org/7737 Tested-by: build bot (Jenkins) Reviewed-by: Stefan Reinauer --- src/soc/nvidia/tegra124/spi.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/src/soc/nvidia/tegra124/spi.c b/src/soc/nvidia/tegra124/spi.c index 841a3c109b..4eb8e5559b 100644 --- a/src/soc/nvidia/tegra124/spi.c +++ b/src/soc/nvidia/tegra124/spi.c @@ -402,6 +402,8 @@ static void tegra_spi_pio_start(struct tegra_spi_channel *spi) { setbits_le32(&spi->regs->trans_status, SPI_STATUS_RDY); setbits_le32(&spi->regs->command1, SPI_CMD1_GO); + /* Make sure the write to command1 completes. */ + read32(&spi->regs->command1); } static inline u32 rx_fifo_count(struct tegra_spi_channel *spi) -- cgit v1.2.3