[net-next PATCH 0/3] add support for impedance control for TI dp83867 phy and fix 2nd ethernet on dra72 rev C evm

[net-next PATCH 0/3] add support for impedance control for TI dp83867 phy and fix 2nd ethernet on dra72 rev C evm

[Mugunthan V N]

Add support for configurable impedance control for TI dp83867
phy via devicetree. More documentation in [1]
CPSW second ethernet is not working, fix it by enabling
impedance configuration on the phy.

Public Datasheet - http://www.ti.com/lit/ds/symlink/dp83867ir.pdf

Mugunthan V N (3):
  net: phy: dp83867: Add documentation for optional impedance control
  net: phy: dp83867: add support for MAC impedance configuration
  ARM: dts: dra72-evm-revc: fix non-working cpsw second ethernet

 .../devicetree/bindings/net/ti,dp83867.txt         |  7 +++++++
 arch/arm/boot/dts/dra72-evm-revc.dts               |  2 ++
 drivers/net/phy/dp83867.c                          | 22 ++++++++++++++++++++++
 3 files changed, 31 insertions(+)

-- 
2.9.2.368.g08bb350

[net-next PATCH 1/3] net: phy: dp83867: Add documentation for optional impedance control

[Mugunthan V N]

Add documention of ti,impedance-control which can be used to
correct MAC impedance mismatch using phy extended registers.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
---
 Documentation/devicetree/bindings/net/ti,dp83867.txt | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/devicetree/bindings/net/ti,dp83867.txt b/Documentation/devicetree/bindings/net/ti,dp83867.txt
index 5d21141..531ea3c5 100644
--- a/Documentation/devicetree/bindings/net/ti,dp83867.txt
+++ b/Documentation/devicetree/bindings/net/ti,dp83867.txt
@@ -9,6 +9,13 @@ Required properties:
 	- ti,fifo-depth - Transmitt FIFO depth- see dt-bindings/net/ti-dp83867.h
 		for applicable values
 
+Optional property:
+	- ti,impedance-control - MAC Interface Impedance control to vary the
+				 output impedance with an approximate range
+				 from 35-70 ohms in 32 steps. Value range can
+				 be 0x0 to 0x1f. Lowest impedance value is
+				 0x1f and highest impedance being 0x0.
+
 Default child nodes are standard Ethernet PHY device
 nodes as described in Documentation/devicetree/bindings/net/phy.txt
 
-- 
2.9.2.368.g08bb350

[net-next PATCH 1/3] net: phy: dp83867: Add documentation for optional impedance control

[Nishanth Menon]

On 07/20/2016 09:56 AM, Mugunthan V N wrote:
> Add documention of ti,impedance-control which can be used to
> correct MAC impedance mismatch using phy extended registers.
>
> Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
> ---
>   Documentation/devicetree/bindings/net/ti,dp83867.txt | 7 +++++++
>   1 file changed, 7 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/net/ti,dp83867.txt b/Documentation/devicetree/bindings/net/ti,dp83867.txt
> index 5d21141..531ea3c5 100644
> --- a/Documentation/devicetree/bindings/net/ti,dp83867.txt
> +++ b/Documentation/devicetree/bindings/net/ti,dp83867.txt
> @@ -9,6 +9,13 @@ Required properties:
>   	- ti,fifo-depth - Transmitt FIFO depth- see dt-bindings/net/ti-dp83867.h
>   		for applicable values
>
> +Optional property:
> +	- ti,impedance-control - MAC Interface Impedance control to vary the
> +				 output impedance with an approximate range
> +				 from 35-70 ohms in 32 steps. Value range can
> +				 be 0x0 to 0x1f. Lowest impedance value is
> +				 0x1f and highest impedance being 0x0.
> +

Should'nt you be using the impedance values of 35 to 70 as the valid 
values here? that would be the hardware description, and the values to 
program corresponding to those are 0x00 to 0x1f. Right?

Rob: is'nt that the right way to do it?

>   Default child nodes are standard Ethernet PHY device
>   nodes as described in Documentation/devicetree/bindings/net/phy.txt
>
>


-- 
Regards,
Nishanth Menon

[net-next PATCH 1/3] net: phy: dp83867: Add documentation for optional impedance control

[Sekhar Nori]

Nishanth,

On Wednesday 20 July 2016 09:03 PM, Nishanth Menon wrote:
> On 07/20/2016 09:56 AM, Mugunthan V N wrote:
>> Add documention of ti,impedance-control which can be used to
>> correct MAC impedance mismatch using phy extended registers.
>>
>> Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
>> ---
>>   Documentation/devicetree/bindings/net/ti,dp83867.txt | 7 +++++++
>>   1 file changed, 7 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/net/ti,dp83867.txt
>> b/Documentation/devicetree/bindings/net/ti,dp83867.txt
>> index 5d21141..531ea3c5 100644
>> --- a/Documentation/devicetree/bindings/net/ti,dp83867.txt
>> +++ b/Documentation/devicetree/bindings/net/ti,dp83867.txt
>> @@ -9,6 +9,13 @@ Required properties:
>>       - ti,fifo-depth - Transmitt FIFO depth- see
>> dt-bindings/net/ti-dp83867.h
>>           for applicable values
>>
>> +Optional property:
>> +    - ti,impedance-control - MAC Interface Impedance control to vary the
>> +                 output impedance with an approximate range
>> +                 from 35-70 ohms in 32 steps. Value range can
>> +                 be 0x0 to 0x1f. Lowest impedance value is
>> +                 0x1f and highest impedance being 0x0.
>> +
> 
> Should'nt you be using the impedance values of 35 to 70 as the valid
> values here? that would be the hardware description, and the values to
> program corresponding to those are 0x00 to 0x1f. Right?
> 
> Rob: is'nt that the right way to do it?

Agree that that is usually the right way to do it. I believe this case
is bit peculiar though. Here is the extract from the datasheet[1] about
how the register in question works.

"
Output impedance approximate range from 35-70 ohms in 32 steps.
Lowest being 11110 and highest being 00000. Range and Step size
will vary with process.

Default is set to 50 ohms by trim. But the default register value can
vary by process. Non default values of MAC I/O impedance can be
used based on trace impedance. Mismatch between device and
trace impedance can cause voltage overshoot and undershoot.
"

So clearly, there is no easy correspondence that the hardware guarantees
between output impedance ohmage and the register value programmed. Only
couple of things are guaranteed.

1) Programming a value of 0 gives approximately 35 ohms
2) Programming a value of 0x1F gives approximately 70 ohms
3) Default value of the register gives 50 ohms (the default value could
vary by device).
4) Programming a value in between will give some ohmage in the
approximate range 35-70 (curve is unknown).

Given this, I am not sure how one can convert a given user supplied ohms
values to a reasonable register value. Clearly, the register is supposed
to be programmed by experimentation, not calculation.

That said, we could take another approach. At least for the current
issue we are trying to address, we only need to configure the register
to max value. And given the nature of the register, I am pretty sure
that is what most people will end up doing.

So, may be we have two properties:

ti,max-output-impedance
ti,min-output-imepdance

which configure the impedance to maximum and minimum values
respectively. If, in future, someone needs to configure a value in
between, he can introduce a more granular property which when then
override whatever else is specified.

Regards,
Sekhar

[1] http://www.ti.com/lit/ds/symlink/dp83867ir.pdf

[net-next PATCH 1/3] net: phy: dp83867: Add documentation for optional impedance control

[Rob Herring]

On Thu, Jul 21, 2016 at 11:52:36AM +0530, Sekhar Nori wrote:
> Nishanth,
> 
> On Wednesday 20 July 2016 09:03 PM, Nishanth Menon wrote:
> > On 07/20/2016 09:56 AM, Mugunthan V N wrote:
> >> Add documention of ti,impedance-control which can be used to
> >> correct MAC impedance mismatch using phy extended registers.
> >>
> >> Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
> >> ---
> >>   Documentation/devicetree/bindings/net/ti,dp83867.txt | 7 +++++++
> >>   1 file changed, 7 insertions(+)
> >>
> >> diff --git a/Documentation/devicetree/bindings/net/ti,dp83867.txt
> >> b/Documentation/devicetree/bindings/net/ti,dp83867.txt
> >> index 5d21141..531ea3c5 100644
> >> --- a/Documentation/devicetree/bindings/net/ti,dp83867.txt
> >> +++ b/Documentation/devicetree/bindings/net/ti,dp83867.txt
> >> @@ -9,6 +9,13 @@ Required properties:
> >>       - ti,fifo-depth - Transmitt FIFO depth- see
> >> dt-bindings/net/ti-dp83867.h
> >>           for applicable values
> >>
> >> +Optional property:
> >> +    - ti,impedance-control - MAC Interface Impedance control to vary the
> >> +                 output impedance with an approximate range
> >> +                 from 35-70 ohms in 32 steps. Value range can
> >> +                 be 0x0 to 0x1f. Lowest impedance value is
> >> +                 0x1f and highest impedance being 0x0.
> >> +
> > 
> > Should'nt you be using the impedance values of 35 to 70 as the valid
> > values here? that would be the hardware description, and the values to
> > program corresponding to those are 0x00 to 0x1f. Right?
> > 
> > Rob: is'nt that the right way to do it?

Normally, yes that is preferred. I don't have an issue with it here if 
that is what makes sense.

> Agree that that is usually the right way to do it. I believe this case
> is bit peculiar though. Here is the extract from the datasheet[1] about
> how the register in question works.
> 
> "
> Output impedance approximate range from 35-70 ohms in 32 steps.
> Lowest being 11110 and highest being 00000. Range and Step size
> will vary with process.
> 
> Default is set to 50 ohms by trim. But the default register value can
> vary by process. Non default values of MAC I/O impedance can be
> used based on trace impedance. Mismatch between device and
> trace impedance can cause voltage overshoot and undershoot.
> "
> 
> So clearly, there is no easy correspondence that the hardware guarantees
> between output impedance ohmage and the register value programmed. Only
> couple of things are guaranteed.
> 
> 1) Programming a value of 0 gives approximately 35 ohms
> 2) Programming a value of 0x1F gives approximately 70 ohms
> 3) Default value of the register gives 50 ohms (the default value could
> vary by device).
> 4) Programming a value in between will give some ohmage in the
> approximate range 35-70 (curve is unknown).
> 
> Given this, I am not sure how one can convert a given user supplied ohms
> values to a reasonable register value. Clearly, the register is supposed
> to be programmed by experimentation, not calculation.

So your are going to change from a known value tuned for the individual 
Si (50ohm) to the same value for all chips (at least for a given board). 
Or does this get set by firmware at boot? If not, seems like you would 
want to specify a delta from the default register value in this case.

> That said, we could take another approach. At least for the current
> issue we are trying to address, we only need to configure the register
> to max value. And given the nature of the register, I am pretty sure
> that is what most people will end up doing.

How does the max value get determined? Possibly it should just be set in 
the kernel.
 
> So, may be we have two properties:
> 
> ti,max-output-impedance
> ti,min-output-imepdance

Just define max if that's all you currently need.

> which configure the impedance to maximum and minimum values
> respectively. If, in future, someone needs to configure a value in
> between, he can introduce a more granular property which when then
> override whatever else is specified.
> 
> Regards,
> Sekhar
> 
> [1] http://www.ti.com/lit/ds/symlink/dp83867ir.pdf

[net-next PATCH 1/3] net: phy: dp83867: Add documentation for optional impedance control

[Mugunthan V N]

Rob,

On Friday 22 July 2016 02:44 AM, Rob Herring wrote:
> On Thu, Jul 21, 2016 at 11:52:36AM +0530, Sekhar Nori wrote:
>> Nishanth,
>>
>> On Wednesday 20 July 2016 09:03 PM, Nishanth Menon wrote:
>>> On 07/20/2016 09:56 AM, Mugunthan V N wrote:
>>>> Add documention of ti,impedance-control which can be used to
>>>> correct MAC impedance mismatch using phy extended registers.
>>>>
>>>> Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
>>>> ---
>>>>   Documentation/devicetree/bindings/net/ti,dp83867.txt | 7 +++++++
>>>>   1 file changed, 7 insertions(+)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/net/ti,dp83867.txt
>>>> b/Documentation/devicetree/bindings/net/ti,dp83867.txt
>>>> index 5d21141..531ea3c5 100644
>>>> --- a/Documentation/devicetree/bindings/net/ti,dp83867.txt
>>>> +++ b/Documentation/devicetree/bindings/net/ti,dp83867.txt
>>>> @@ -9,6 +9,13 @@ Required properties:
>>>>       - ti,fifo-depth - Transmitt FIFO depth- see
>>>> dt-bindings/net/ti-dp83867.h
>>>>           for applicable values
>>>>
>>>> +Optional property:
>>>> +    - ti,impedance-control - MAC Interface Impedance control to vary the
>>>> +                 output impedance with an approximate range
>>>> +                 from 35-70 ohms in 32 steps. Value range can
>>>> +                 be 0x0 to 0x1f. Lowest impedance value is
>>>> +                 0x1f and highest impedance being 0x0.
>>>> +
>>>
>>> Should'nt you be using the impedance values of 35 to 70 as the valid
>>> values here? that would be the hardware description, and the values to
>>> program corresponding to those are 0x00 to 0x1f. Right?
>>>
>>> Rob: is'nt that the right way to do it?
> 
> Normally, yes that is preferred. I don't have an issue with it here if 
> that is what makes sense.
> 
>> Agree that that is usually the right way to do it. I believe this case
>> is bit peculiar though. Here is the extract from the datasheet[1] about
>> how the register in question works.
>>
>> "
>> Output impedance approximate range from 35-70 ohms in 32 steps.
>> Lowest being 11110 and highest being 00000. Range and Step size
>> will vary with process.
>>
>> Default is set to 50 ohms by trim. But the default register value can
>> vary by process. Non default values of MAC I/O impedance can be
>> used based on trace impedance. Mismatch between device and
>> trace impedance can cause voltage overshoot and undershoot.
>> "
>>
>> So clearly, there is no easy correspondence that the hardware guarantees
>> between output impedance ohmage and the register value programmed. Only
>> couple of things are guaranteed.
>>
>> 1) Programming a value of 0 gives approximately 35 ohms
>> 2) Programming a value of 0x1F gives approximately 70 ohms
>> 3) Default value of the register gives 50 ohms (the default value could
>> vary by device).
>> 4) Programming a value in between will give some ohmage in the
>> approximate range 35-70 (curve is unknown).

Sekhar got it wrong, programming 0x1F provides the minimum impedance of
35 ohms and 0x0 provides the maximum impedance of 70 ohms.

>>
>> Given this, I am not sure how one can convert a given user supplied ohms
>> values to a reasonable register value. Clearly, the register is supposed
>> to be programmed by experimentation, not calculation.
> 
> So your are going to change from a known value tuned for the individual 
> Si (50ohm) to the same value for all chips (at least for a given board). 
> Or does this get set by firmware at boot? If not, seems like you would 
> want to specify a delta from the default register value in this case.

The delta will not be constant for each steps of the register content.
So this approach cannot be taken.

> 
>> That said, we could take another approach. At least for the current
>> issue we are trying to address, we only need to configure the register
>> to max value. And given the nature of the register, I am pretty sure
>> that is what most people will end up doing.
> 
> How does the max value get determined? Possibly it should just be set in 
> the kernel.

Yes, the min/max value will be determined in the kernel and the DT will
have either of the properties below.

>  
>> So, may be we have two properties:
>>
>> ti,max-output-impedance
>> ti,min-output-imepdance
> 
> Just define max if that's all you currently need.

Currently we care about only the min-output-impedance (register content
0x1f). Will respin the patch using ti,min-output-impedance.

Regards
Mugunthan V N

[net-next PATCH 2/3] net: phy: dp83867: add support for MAC impedance configuration

[Mugunthan V N]

Add support for programmable MAC impedance configuration

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
---
 drivers/net/phy/dp83867.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/drivers/net/phy/dp83867.c b/drivers/net/phy/dp83867.c
index 91177a4..ace3558 100644
--- a/drivers/net/phy/dp83867.c
+++ b/drivers/net/phy/dp83867.c
@@ -33,6 +33,7 @@
 /* Extended Registers */
 #define DP83867_RGMIICTL	0x0032
 #define DP83867_RGMIIDCTL	0x0086
+#define DP83867_IO_MUX_CFG	0x0170
 
 #define DP83867_SW_RESET	BIT(15)
 #define DP83867_SW_RESTART	BIT(14)
@@ -62,10 +63,14 @@
 /* RGMIIDCTL bits */
 #define DP83867_RGMII_TX_CLK_DELAY_SHIFT	4
 
+/* IO_MUX_CFG bits */
+#define DP83867_IO_MUX_CFG_IO_IMPEDANCE_CTRL	0x1F
+
 struct dp83867_private {
 	int rx_id_delay;
 	int tx_id_delay;
 	int fifo_depth;
+	int io_impedance;
 };
 
 static int dp83867_ack_interrupt(struct phy_device *phydev)
@@ -111,6 +116,12 @@ static int dp83867_of_init(struct phy_device *phydev)
 	if (!of_node)
 		return -ENODEV;
 
+	dp83867->io_impedance = -EINVAL;
+
+	/* Optional configuration */
+	of_property_read_u32(of_node, "ti,impedance-control",
+			     &dp83867->io_impedance);
+
 	ret = of_property_read_u32(of_node, "ti,rx-internal-delay",
 				   &dp83867->rx_id_delay);
 	if (ret)
@@ -184,6 +195,17 @@ static int dp83867_config_init(struct phy_device *phydev)
 
 		phy_write_mmd_indirect(phydev, DP83867_RGMIIDCTL,
 				       DP83867_DEVADDR, delay);
+
+		if (dp83867->io_impedance >= 0) {
+			val = phy_read_mmd_indirect(phydev,
+						    DP83867_IO_MUX_CFG,
+						    DP83867_DEVADDR);
+			val &= ~DP83867_IO_MUX_CFG_IO_IMPEDANCE_CTRL;
+			val |= dp83867->io_impedance &
+			       DP83867_IO_MUX_CFG_IO_IMPEDANCE_CTRL;
+			phy_write_mmd_indirect(phydev, DP83867_IO_MUX_CFG,
+					       DP83867_DEVADDR, val);
+		}
 	}
 
 	return 0;
-- 
2.9.2.368.g08bb350

[net-next PATCH 3/3] ARM: dts: dra72-evm-revc: fix non-working cpsw second ethernet

[Mugunthan V N]

Second ethernet of cpsw is not working, make it work by adding
impedance configuration.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
---
 arch/arm/boot/dts/dra72-evm-revc.dts | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm/boot/dts/dra72-evm-revc.dts b/arch/arm/boot/dts/dra72-evm-revc.dts
index f9cfd3b..4313de5 100644
--- a/arch/arm/boot/dts/dra72-evm-revc.dts
+++ b/arch/arm/boot/dts/dra72-evm-revc.dts
@@ -69,5 +69,7 @@
 		ti,rx-internal-delay = <DP83867_RGMIIDCTL_2_00_NS>;
 		ti,tx-internal-delay = <DP83867_RGMIIDCTL_1_NS>;
 		ti,fifo-depth = <DP83867_PHYCR_FIFO_DEPTH_8_B_NIB>;
+		ti,impedance-control = <0x1f>;
 	};
 };
+
-- 
2.9.2.368.g08bb350