From: Thommy Jakobsson thommyj@gmail.com
[ Upstream commit 5dd8304981ecffa77bb72b1c57c4be5dfe6cfae9 ]
In the public interface for chipselect, there is always an entry commented as "Dummy generic FIFO entry" pushed down to the fifo right after the activate/deactivate command. The dummy entry is 0x0, irregardless if the intention was to activate or deactive the cs. This causes the cs line to glitch rather than beeing activated in the case when there was an activate command.
This has been observed on oscilloscope, and have caused problems for at least one specific flash device type connected to the qspi port. After the change the glitch is gone and cs goes active when intended.
The reason why this worked before (except for the glitch) was because when sending the actual data, the CS bits are once again set. Since most flashes uses mode 0, there is always a half clk period anyway for cs to clk active setup time. If someone would rely on timing from a chip_select call to a transfer_one, it would fail though.
It is unknown why the dummy entry was there in the first place, git log seems to be of no help in this case. The reference manual gives no indication of the necessity of this. In fact the lower 8 bits are a setup (or hold in case of deactivate) time expressed in cycles. So this should not be needed to fulfill any setup/hold timings.
Signed-off-by: Thommy Jakobsson thommyj@gmail.com Reviewed-by: Naga Sureshkumar Relli naga.sureshkumar.relli@xilinx.com Link: https://lore.kernel.org/r/20200224162643.29102-1-thommyj@gmail.com Signed-off-by: Mark Brown broonie@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/spi/spi-zynqmp-gqspi.c | 3 --- 1 file changed, 3 deletions(-)
diff --git a/drivers/spi/spi-zynqmp-gqspi.c b/drivers/spi/spi-zynqmp-gqspi.c index 60c4de4e44856..7412a3042a8d2 100644 --- a/drivers/spi/spi-zynqmp-gqspi.c +++ b/drivers/spi/spi-zynqmp-gqspi.c @@ -401,9 +401,6 @@ static void zynqmp_qspi_chipselect(struct spi_device *qspi, bool is_high)
zynqmp_gqspi_write(xqspi, GQSPI_GEN_FIFO_OFST, genfifoentry);
- /* Dummy generic FIFO entry */ - zynqmp_gqspi_write(xqspi, GQSPI_GEN_FIFO_OFST, 0x0); - /* Manually start the generic FIFO command */ zynqmp_gqspi_write(xqspi, GQSPI_CONFIG_OFST, zynqmp_gqspi_read(xqspi, GQSPI_CONFIG_OFST) |