sf: Add dual memories support - DUAL_PARALLEL
This patch added support for accessing dual memories in
parallel connection with single chipselect line from controller.
For more info - see doc/SPI/README.dual-flash
Signed-off-by: Jagannadha Sutradharudu Teki <jaganna@xilinx.com>
diff --git a/doc/SPI/README.dual-flash b/doc/SPI/README.dual-flash
index ba0aa26..6c88d65 100644
--- a/doc/SPI/README.dual-flash
+++ b/doc/SPI/README.dual-flash
@@ -54,6 +54,33 @@
by default, if U_PAGE is unset lower memory should accessible,
once user wants to access upper memory need to set U_PAGE.
+SPI_FLASH_CONN_DUALPARALLEL:
+ - dual spi/qspi flash memories are connected with a single chipselect
+ line and these two memories are operating parallel with separate buses.
+ - xilinx zynq qspi controller has implemented this feature [1]
+
+ +-------------+ CS +---------------+
+ | |---------------------->| |
+ | | I0[3:0] | Upper Flash |
+ | |<=====================>| memory |
+ | | CLK | (SPI/QSPI) |
+ | |---------------------->| |
+ | Controller | CS +---------------+
+ | SPI/QSPI |---------------------->| |
+ | | I0[3:0] | Lower Flash |
+ | |<=====================>| memory |
+ | | CLK | (SPI/QSPI) |
+ | |---------------------->| |
+ +-------------+ +---------------+
+
+ - two memory flash devices should has same hw part attributes (like size,
+ vendor..etc)
+ - Configurations:
+ Need to enable SEP_BUS[BIT:29],TWO_MEM[BIT:30] on LQSPI_CFG register.
+ - Operation:
+ Even bits, i.e. bit 0, 2, 4 ., of a data word is located in the lower memory
+ and odd bits, i.e. bit 1, 3, 5, ., of a data word is located in the upper memory.
+
Note: Technically there is only one CS line from the controller, but
zynq qspi controller has an internal hw logic to enable additional CS
when controller is configured for dual memories.