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This patch is to add a documentation for ptp_qoriq dt-bindings. The description for ptp_qoriq dt-bindings was actually moved from Documentation/devicetree/bindings/net/fsl-tsec-phy.txt, since gianfar_ptp driver was moved to ptp_qoriq driver. Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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* Freescale QorIQ 1588 timer based PTP clock | ||
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General Properties: | ||
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- compatible Should be "fsl,etsec-ptp" | ||
- reg Offset and length of the register set for the device | ||
- interrupts There should be at least two interrupts. Some devices | ||
have as many as four PTP related interrupts. | ||
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Clock Properties: | ||
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- fsl,cksel Timer reference clock source. | ||
- fsl,tclk-period Timer reference clock period in nanoseconds. | ||
- fsl,tmr-prsc Prescaler, divides the output clock. | ||
- fsl,tmr-add Frequency compensation value. | ||
- fsl,tmr-fiper1 Fixed interval period pulse generator. | ||
- fsl,tmr-fiper2 Fixed interval period pulse generator. | ||
- fsl,max-adj Maximum frequency adjustment in parts per billion. | ||
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These properties set the operational parameters for the PTP | ||
clock. You must choose these carefully for the clock to work right. | ||
Here is how to figure good values: | ||
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TimerOsc = selected reference clock MHz | ||
tclk_period = desired clock period nanoseconds | ||
NominalFreq = 1000 / tclk_period MHz | ||
FreqDivRatio = TimerOsc / NominalFreq (must be greater that 1.0) | ||
tmr_add = ceil(2^32 / FreqDivRatio) | ||
OutputClock = NominalFreq / tmr_prsc MHz | ||
PulseWidth = 1 / OutputClock microseconds | ||
FiperFreq1 = desired frequency in Hz | ||
FiperDiv1 = 1000000 * OutputClock / FiperFreq1 | ||
tmr_fiper1 = tmr_prsc * tclk_period * FiperDiv1 - tclk_period | ||
max_adj = 1000000000 * (FreqDivRatio - 1.0) - 1 | ||
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The calculation for tmr_fiper2 is the same as for tmr_fiper1. The | ||
driver expects that tmr_fiper1 will be correctly set to produce a 1 | ||
Pulse Per Second (PPS) signal, since this will be offered to the PPS | ||
subsystem to synchronize the Linux clock. | ||
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Reference clock source is determined by the value, which is holded | ||
in CKSEL bits in TMR_CTRL register. "fsl,cksel" property keeps the | ||
value, which will be directly written in those bits, that is why, | ||
according to reference manual, the next clock sources can be used: | ||
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<0> - external high precision timer reference clock (TSEC_TMR_CLK | ||
input is used for this purpose); | ||
<1> - eTSEC system clock; | ||
<2> - eTSEC1 transmit clock; | ||
<3> - RTC clock input. | ||
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When this attribute is not used, eTSEC system clock will serve as | ||
IEEE 1588 timer reference clock. | ||
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Example: | ||
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ptp_clock@24e00 { | ||
compatible = "fsl,etsec-ptp"; | ||
reg = <0x24E00 0xB0>; | ||
interrupts = <12 0x8 13 0x8>; | ||
interrupt-parent = < &ipic >; | ||
fsl,cksel = <1>; | ||
fsl,tclk-period = <10>; | ||
fsl,tmr-prsc = <100>; | ||
fsl,tmr-add = <0x999999A4>; | ||
fsl,tmr-fiper1 = <0x3B9AC9F6>; | ||
fsl,tmr-fiper2 = <0x00018696>; | ||
fsl,max-adj = <659999998>; | ||
}; |