a4cc96d1f0
Edge-rate: As system and networking speeds increase, a signal's output transition, also know as the edge rate or slew rate (V/ns), takes on greater importance because high-speed signals come with a price. That price is an assortment of interference problems like ringing on the line, signal overshoot and undershoot, extended signal settling times, crosstalk noise, transmission line reflections, false signal detection by the receiving device and electromagnetic interference (EMI) -- all of which can negate the potential gains designers are seeking when they try to increase system speeds through the use of higher performance logic devices. The fact is, faster signaling edge rates can cause a higher level of electrical noise or other type of interference that can actually lead to slower line speeds and lower maximum system frequencies. This parameter allow the board designers to change the driving strange, and thereby change the EMI behavioral. Edge-rate parameters (vddmac, edge-slowdown) get from Device Tree. Tested on Beaglebone Black with VSC 8531 PHY. Signed-off-by: Raju Lakkaraju <Raju.Lakkaraju@microsemi.com> Signed-off-by: David S. Miller <davem@davemloft.net>
59 lines
2.2 KiB
Plaintext
59 lines
2.2 KiB
Plaintext
* Microsemi - vsc8531 Giga bit ethernet phy
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Required properties:
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- compatible : Should contain phy id as "ethernet-phy-idAAAA.BBBB"
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The PHY device uses the binding described in
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Documentation/devicetree/bindings/net/phy.txt
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Optional properties:
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- vsc8531,vddmac : The vddmac in mV.
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- vsc8531,edge-slowdown : % the edge should be slowed down relative to
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the fastest possible edge time. Native sign
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need not enter.
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Edge rate sets the drive strength of the MAC
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interface output signals. Changing the drive
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strength will affect the edge rate of the output
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signal. The goal of this setting is to help
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reduce electrical emission (EMI) by being able
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to reprogram drive strength and in effect slow
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down the edge rate if desired. Table 1 shows the
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impact to the edge rate per VDDMAC supply for each
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drive strength setting.
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Ref: Table:1 - Edge rate change below.
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Note: see dt-bindings/net/mscc-phy-vsc8531.h for applicable values
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Table: 1 - Edge rate change
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----------------------------------------------------------------|
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| Edge Rate Change (VDDMAC) |
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| 3300 mV 2500 mV 1800 mV 1500 mV |
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|---------------------------------------------------------------|
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| Default Deafult Default Default |
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| (Fastest) (recommended) (recommended) |
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|---------------------------------------------------------------|
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| -2% -3% -5% -6% |
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|---------------------------------------------------------------|
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| -4% -6% -9% -14% |
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|---------------------------------------------------------------|
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| -7% -10% -16% -21% |
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|(recommended) (recommended) |
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|---------------------------------------------------------------|
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| -10% -14% -23% -29% |
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|---------------------------------------------------------------|
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| -17% -23% -35% -42% |
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|---------------------------------------------------------------|
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| -29% -37% -52% -58% |
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|---------------------------------------------------------------|
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| -53% -63% -76% -77% |
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| (slowest) |
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|---------------------------------------------------------------|
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Example:
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vsc8531_0: ethernet-phy@0 {
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compatible = "ethernet-phy-id0007.0570";
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vsc8531,vddmac = <3300>;
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vsc8531,edge-slowdown = <21>;
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};
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