From 76b17e6e4923e4138ed9a4d480cba148ff239dc9 Mon Sep 17 00:00:00 2001 From: Julius Werner Date: Thu, 26 Mar 2015 16:30:25 -0700 Subject: spi/rockchip: Add device tree property to configure Rx Sample Delay We have found that we can sometimes see read failures on boards with high-capacitance SPI lines. It seems that the controller samples the Rx data line too early, and its register interface has an "Rx Sample Delay" setting to fine-tune against this issue. This patch adds a new optional device tree entry that can configure this delay in terms of nanoseconds. The kernel will calculate the best-fitting amount of parent clock ticks to program the controller with based on that. Signed-off-by: Julius Werner Signed-off-by: Mark Brown --- Documentation/devicetree/bindings/spi/spi-rockchip.txt | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'Documentation') diff --git a/Documentation/devicetree/bindings/spi/spi-rockchip.txt b/Documentation/devicetree/bindings/spi/spi-rockchip.txt index 467dec441c62..0c491bda4c65 100644 --- a/Documentation/devicetree/bindings/spi/spi-rockchip.txt +++ b/Documentation/devicetree/bindings/spi/spi-rockchip.txt @@ -24,6 +24,9 @@ Optional Properties: - dmas: DMA specifiers for tx and rx dma. See the DMA client binding, Documentation/devicetree/bindings/dma/dma.txt - dma-names: DMA request names should include "tx" and "rx" if present. +- rx-sample-delay-ns: nanoseconds to delay after the SCLK edge before sampling + Rx data (may need to be fine tuned for high capacitance lines). + No delay (0) by default. Example: @@ -33,6 +36,7 @@ Example: reg = <0xff110000 0x1000>; dmas = <&pdma1 11>, <&pdma1 12>; dma-names = "tx", "rx"; + rx-sample-delay-ns = <10>; #address-cells = <1>; #size-cells = <0>; interrupts = ; -- cgit v1.2.3