summaryrefslogtreecommitdiffstats
path: root/Documentation/blackfin/bfin-spi-notes.txt
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/blackfin/bfin-spi-notes.txt')
-rw-r--r--Documentation/blackfin/bfin-spi-notes.txt14
1 files changed, 14 insertions, 0 deletions
diff --git a/Documentation/blackfin/bfin-spi-notes.txt b/Documentation/blackfin/bfin-spi-notes.txt
new file mode 100644
index 000000000000..556fa877f2e8
--- /dev/null
+++ b/Documentation/blackfin/bfin-spi-notes.txt
@@ -0,0 +1,14 @@
+SPI Chip Select behavior:
+
+With the Blackfin on-chip SPI peripheral, there is some logic tied to the CPHA
+bit whether the Slave Select Line is controlled by hardware (CPHA=0) or
+controlled by software (CPHA=1). However, the Linux SPI bus driver assumes that
+the Slave Select is always under software control and being asserted during
+the entire SPI transfer. - And not just bits_per_word duration.
+
+In most cases you can utilize SPI MODE_3 instead of MODE_0 to work-around this
+behavior. If your SPI slave device in question requires SPI MODE_0 or MODE_2
+timing, you can utilize the GPIO controlled SPI Slave Select option instead.
+
+You can even use the same pin whose peripheral role is a SSEL,
+but use it as a GPIO instead.