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serial: tegra: DT for Adjusted baud rates

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Tegra186 chip has a hardware issue resulting in frame errors when
tolerance level for baud rate is negative. Provided entries to adjust
baud rate to be within acceptable range and work with devices that
can send negative baud rate. Also report error when baud rate set is
out of tolerance range of controller updated in device tree.

Signed-off-by: Krishna Yarlagadda <kyarlagadda@nvidia.com>
Link: https://lore.kernel.org/r/1567572187-29820-10-git-send-email-kyarlagadda@nvidia.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Krishna Yarlagadda 2019-09-04 10:13:04 +05:30 committed by Greg Kroah-Hartman
parent 7799a3aa81
commit d90fd87bab
1 changed files with 32 additions and 0 deletions
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32
Documentation/devicetree/bindings/serial/nvidia,tegra20-hsuart.txt
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@ -24,6 +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:
@ -38,4 +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 */
};