serial: tegra: DT for Adjusted baud rates

[linux.git] / Documentation / devicetree / bindings / serial / nvidia,tegra20-hsuart.txt

diff --git a/Documentation/devicetree/bindings/serial/nvidia,tegra20-hsuart.txt b/Documentation/devicetree/bindings/serial/nvidia,tegra20-hsuart.txt
index d7edf732eb7f5716f8feb5e9d8398cb8a3ac1dbc..f709304036c23a05c3ba2fe2fbc57fe6c37e475e 100644 (file)
--- 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 */
 };