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2023-12-08 01573e231f18eb2d99162747186f59511f56b64d

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