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Diffstat (limited to 'Documentation/devicetree/bindings/serial/nvidia,tegra20-hsuart.txt')
| -rw-r--r-- | Documentation/devicetree/bindings/serial/nvidia,tegra20-hsuart.txt | 39 |
1 files changed, 38 insertions, 1 deletions
diff --git a/Documentation/devicetree/bindings/serial/nvidia,tegra20-hsuart.txt b/Documentation/devicetree/bindings/serial/nvidia,tegra20-hsuart.txt index d7edf732eb7f..f709304036c2 100644 --- a/Documentation/devicetree/bindings/serial/nvidia,tegra20-hsuart.txt +++ b/Documentation/devicetree/bindings/serial/nvidia,tegra20-hsuart.txt @@ -1,7 +1,12 @@ NVIDIA Tegra20/Tegra30 high speed (DMA based) UART controller driver. Required properties: -- compatible : should be "nvidia,tegra30-hsuart", "nvidia,tegra20-hsuart". +- compatible : should be, + "nvidia,tegra20-hsuart" for Tegra20, + "nvidia,tegra30-hsuart" for Tegra30, + "nvidia,tegra186-hsuart" for Tegra186, + "nvidia,tegra194-hsuart" for Tegra194. + - reg: Should contain UART controller registers location and length. - interrupts: Should contain UART controller interrupts. - clocks: Must contain one entry, for the module clock. @@ -19,6 +24,37 @@ Required properties: Optional properties: - nvidia,enable-modem-interrupt: Enable modem interrupts. Should be enable only if all 8 lines of UART controller are pinmuxed. +- nvidia,adjust-baud-rates: List of entries providing percentage of baud rate + adjustment within a range. + Each entry contains sets of 3 values. Range low/high and adjusted rate. + <range_low range_high adjusted_rate> + When baud rate set on controller falls within the range mentioned in this + field, baud rate will be adjusted by percentage mentioned here. + Ex: <9600 115200 200> + Increase baud rate by 2% when set baud rate falls within range 9600 to 115200 + +Baud Rate tolerance: + Standard UART devices are expected to have tolerance for baud rate error by + -4 to +4 %. All Tegra devices till Tegra210 had this support. However, + Tegra186 chip has a known hardware issue. UART Rx baud rate tolerance level + is 0% to +4% in 1-stop config. Otherwise, the received data will have + corruption/invalid framing errors. Parker errata suggests adjusting baud + rate to be higher than the deviations observed in Tx. + + Tx deviation of connected device can be captured over scope (or noted from + its spec) for valid range and Tegra baud rate has to be set above actual + Tx baud rate observed. To do this we use nvidia,adjust-baud-rates + + As an example, consider there is deviation observed in Tx for baud rates as + listed below. + 0 to 9600 has 1% deviation + 9600 to 115200 2% deviation + This slight deviation is expcted and Tegra UART is expected to handle it. Due + to the issue stated above, baud rate on Tegra UART should be set equal to or + above deviation observed for avoiding frame errors. + Property should be set like this + nvidia,adjust-baud-rates = <0 9600 100>, + <9600 115200 200>; Example: @@ -33,4 +69,5 @@ serial@70006000 { reset-names = "serial"; dmas = <&apbdma 8>, <&apbdma 8>; dma-names = "rx", "tx"; + nvidia,adjust-baud-rates = <1000000 4000000 136>; /* 1.36% shift */ }; |