Update the dw-apb-ssi binding document, to add an optional 'cs-override' devicetree property. This property adds the ability for dw spi controller driver to work with the dw spi controller found on Alpine chips. The dw spi controller has an auto-deselect of Chip-Select, in case there is no data inside the Tx FIFO. While working on platforms with Alpine chips, auto-deselect mode causes an issue for some spi devices that can't handle the Chip-Select deselect in the middle of a transaction. It is a normal behavior for a Tx FIFO to be empty in the middle of a transaction, due to busy cpu. In the Alpine chip family an option to change the default behavior was added to the original dw spi controller to prevent this issue of de-asserting Chip-Select once TX FIFO is empty. The change was to allow SW to force the Chip-Select. With this change, as long as the Slave Enable Register is asserted, the Chip-Select will be asserted. As a result, it is necessary to deselect the Slave Select Register once the transaction is done. This feature is enabled via a device property called 'cs-override'. Once the driver identifies the 'cs-override' property, it enables the hw fixup logic, by writing to a dedicated register found in the IP reserved area and will starts deselecting the Slave Select Register when the transfer ends. Signed-off-by: Talel Shenhar <talel@xxxxxxxxxx> Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx> --- Documentation/devicetree/bindings/spi/snps,dw-apb-ssi.txt | 2 ++ 1 file changed, 2 insertions(+) diff --git a/Documentation/devicetree/bindings/spi/snps,dw-apb-ssi.txt b/Documentation/devicetree/bindings/spi/snps,dw-apb-ssi.txt index 642d3fb..dd366f5 100644 --- a/Documentation/devicetree/bindings/spi/snps,dw-apb-ssi.txt +++ b/Documentation/devicetree/bindings/spi/snps,dw-apb-ssi.txt @@ -14,6 +14,8 @@ Optional properties: - num-cs : The number of chipselects. If omitted, this will default to 4. - reg-io-width : The I/O register width (in bytes) implemented by this device. Supported values are 2 or 4 (the default). +- cs-override: Enable explicit Chip-Select deselect during transfer instead of + default auto-deselect upon tx FIFO becoming empty. Child nodes as per the generic SPI binding. -- 2.7.4
