From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Device-tree bindings for MDIO define per-PHY reset-gpios as well as a
global reset-gpios property at the MDIO node level which controlls all
devices on the bus. The latter is most likely a workaround for the
chicken-and-egg problem where we cannot read the ID of the PHY before
bringing it out of reset but we cannot bring it out of reset until we've
read its ID.
I have proposed a solution for this problem in 2020 but it never got
upstream. Now we have a workaround in place which allows us to hard-code
the PHY id in the compatible property, thus skipping the ID scanning).
Let's make the device-tree for sa8775p-ride slightly more correct by
moving the reset-gpios property to the PHY node with its ID put into the
PHY node's compatible.
Link: https://lore.kernel.org/all/20200622093744.13685-1-brgl@bgdev.pl/
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
arch/arm64/boot/dts/qcom/sa8775p-ride.dts | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/boot/dts/qcom/sa8775p-ride.dts b/arch/arm64/boot/dts/qcom/sa8775p-ride.dts
index 38327aff18b0..1c471278d441 100644
--- a/arch/arm64/boot/dts/qcom/sa8775p-ride.dts
+++ b/arch/arm64/boot/dts/qcom/sa8775p-ride.dts
@@ -279,13 +279,12 @@ mdio {
#address-cells = <1>;
#size-cells = <0>;
- reset-gpios = <&pmm8654au_2_gpios 8 GPIO_ACTIVE_LOW>;
- reset-delay-us = <11000>;
- reset-post-delay-us = <70000>;
-
sgmii_phy: phy@8 {
+ compatible = "ethernet-phy-id0141.0dd4";
reg = <0x8>;
device_type = "ethernet-phy";
+ reset-gpios = <&pmm8654au_2_gpios 8 GPIO_ACTIVE_LOW>;
+ reset-deassert-us = <70000>;
};
};
--
2.39.2On Mon, Aug 07, 2023 at 09:35:03PM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>
> Device-tree bindings for MDIO define per-PHY reset-gpios as well as a
> global reset-gpios property at the MDIO node level which controlls all
s/controlls/controls/
> devices on the bus. The latter is most likely a workaround for the
> chicken-and-egg problem where we cannot read the ID of the PHY before
> bringing it out of reset but we cannot bring it out of reset until we've
> read its ID.
>
> I have proposed a solution for this problem in 2020 but it never got
> upstream. Now we have a workaround in place which allows us to hard-code
> the PHY id in the compatible property, thus skipping the ID scanning).
nitpicky, but I think that already existed at that time :D
>
> Let's make the device-tree for sa8775p-ride slightly more correct by
> moving the reset-gpios property to the PHY node with its ID put into the
> PHY node's compatible.
>
> Link: https://lore.kernel.org/all/20200622093744.13685-1-brgl@bgdev.pl/
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
> ---
> arch/arm64/boot/dts/qcom/sa8775p-ride.dts | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/boot/dts/qcom/sa8775p-ride.dts b/arch/arm64/boot/dts/qcom/sa8775p-ride.dts
> index 38327aff18b0..1c471278d441 100644
> --- a/arch/arm64/boot/dts/qcom/sa8775p-ride.dts
> +++ b/arch/arm64/boot/dts/qcom/sa8775p-ride.dts
> @@ -279,13 +279,12 @@ mdio {
> #address-cells = <1>;
> #size-cells = <0>;
>
> - reset-gpios = <&pmm8654au_2_gpios 8 GPIO_ACTIVE_LOW>;
> - reset-delay-us = <11000>;
> - reset-post-delay-us = <70000>;
> -
> sgmii_phy: phy@8 {
> + compatible = "ethernet-phy-id0141.0dd4";
> reg = <0x8>;
> device_type = "ethernet-phy";
> + reset-gpios = <&pmm8654au_2_gpios 8 GPIO_ACTIVE_LOW>;
> + reset-deassert-us = <70000>;
Doesn't this need reset-assert-us?
> > I have proposed a solution for this problem in 2020 but it never got
> > upstream. Now we have a workaround in place which allows us to hard-code
> > the PHY id in the compatible property, thus skipping the ID scanning).
>
> nitpicky, but I think that already existed at that time :D
Yes, it has been there are long long time. It is however only in the
last 5 years of so has it been seen as a solution to the chicken egg
problem.
> > sgmii_phy: phy@8 {
> > + compatible = "ethernet-phy-id0141.0dd4";
> > reg = <0x8>;
> > device_type = "ethernet-phy";
> > + reset-gpios = <&pmm8654au_2_gpios 8 GPIO_ACTIVE_LOW>;
> > + reset-deassert-us = <70000>;
>
> Doesn't this need reset-assert-us?
If i remember correctly, there is a default value if DT does not
provide one.
Andrew
On Mon, Aug 07, 2023 at 11:51:40PM +0200, Andrew Lunn wrote:
> > > I have proposed a solution for this problem in 2020 but it never got
> > > upstream. Now we have a workaround in place which allows us to hard-code
> > > the PHY id in the compatible property, thus skipping the ID scanning).
> >
> > nitpicky, but I think that already existed at that time :D
>
> Yes, it has been there are long long time. It is however only in the
> last 5 years of so has it been seen as a solution to the chicken egg
> problem.
>
> > > sgmii_phy: phy@8 {
> > > + compatible = "ethernet-phy-id0141.0dd4";
> > > reg = <0x8>;
> > > device_type = "ethernet-phy";
> > > + reset-gpios = <&pmm8654au_2_gpios 8 GPIO_ACTIVE_LOW>;
> > > + reset-deassert-us = <70000>;
> >
> > Doesn't this need reset-assert-us?
>
> If i remember correctly, there is a default value if DT does not
> provide one.
>
I've been trying to make sure I view devicetree properties as an OS
agnostic ABI lately, with that in mind...
The dt-binding says this for ethernet-phy:
reset-assert-us:
description:
Delay after the reset was asserted in microseconds. If this
property is missing the delay will be skipped.
If the hardware needs a delay I think we should encode it based on that
description, else we risk it starting to look like a unit impulse!
On Tue, Aug 8, 2023 at 12:27 AM Andrew Halaney <ahalaney@redhat.com> wrote:
>
> On Mon, Aug 07, 2023 at 11:51:40PM +0200, Andrew Lunn wrote:
> > > > I have proposed a solution for this problem in 2020 but it never got
> > > > upstream. Now we have a workaround in place which allows us to hard-code
> > > > the PHY id in the compatible property, thus skipping the ID scanning).
> > >
> > > nitpicky, but I think that already existed at that time :D
> >
> > Yes, it has been there are long long time. It is however only in the
> > last 5 years of so has it been seen as a solution to the chicken egg
> > problem.
> >
> > > > sgmii_phy: phy@8 {
> > > > + compatible = "ethernet-phy-id0141.0dd4";
> > > > reg = <0x8>;
> > > > device_type = "ethernet-phy";
> > > > + reset-gpios = <&pmm8654au_2_gpios 8 GPIO_ACTIVE_LOW>;
> > > > + reset-deassert-us = <70000>;
> > >
> > > Doesn't this need reset-assert-us?
> >
> > If i remember correctly, there is a default value if DT does not
> > provide one.
> >
>
> I've been trying to make sure I view devicetree properties as an OS
> agnostic ABI lately, with that in mind...
>
> The dt-binding says this for ethernet-phy:
>
> reset-assert-us:
> description:
> Delay after the reset was asserted in microseconds. If this
> property is missing the delay will be skipped.
>
> If the hardware needs a delay I think we should encode it based on that
> description, else we risk it starting to look like a unit impulse!
>
Please note that the mdio-level delay properties are not the same as
the ones on the PHY levels.
reset-delay-us - this is the delay BEFORE *DEASSERTING* the reset line
reset-post-delay-us - this is the delay AFTER *DEASSERTING* the reset line
On PHY level we have:
reset-assert-us - AFTER *ASSERTING*
reset-deassert-us - AFTER *DEASSERTING*
There never has been any reset-assert delay on that line before. It
doesn't look like we need a delay BEFORE deasserting the line, do we?
Bart
On Tue, Aug 08, 2023 at 02:16:50PM +0200, Bartosz Golaszewski wrote:
> On Tue, Aug 8, 2023 at 12:27 AM Andrew Halaney <ahalaney@redhat.com> wrote:
> >
> > On Mon, Aug 07, 2023 at 11:51:40PM +0200, Andrew Lunn wrote:
> > > > > I have proposed a solution for this problem in 2020 but it never got
> > > > > upstream. Now we have a workaround in place which allows us to hard-code
> > > > > the PHY id in the compatible property, thus skipping the ID scanning).
> > > >
> > > > nitpicky, but I think that already existed at that time :D
> > >
> > > Yes, it has been there are long long time. It is however only in the
> > > last 5 years of so has it been seen as a solution to the chicken egg
> > > problem.
> > >
> > > > > sgmii_phy: phy@8 {
> > > > > + compatible = "ethernet-phy-id0141.0dd4";
> > > > > reg = <0x8>;
> > > > > device_type = "ethernet-phy";
> > > > > + reset-gpios = <&pmm8654au_2_gpios 8 GPIO_ACTIVE_LOW>;
> > > > > + reset-deassert-us = <70000>;
> > > >
> > > > Doesn't this need reset-assert-us?
> > >
> > > If i remember correctly, there is a default value if DT does not
> > > provide one.
> > >
> >
> > I've been trying to make sure I view devicetree properties as an OS
> > agnostic ABI lately, with that in mind...
> >
> > The dt-binding says this for ethernet-phy:
> >
> > reset-assert-us:
> > description:
> > Delay after the reset was asserted in microseconds. If this
> > property is missing the delay will be skipped.
> >
> > If the hardware needs a delay I think we should encode it based on that
> > description, else we risk it starting to look like a unit impulse!
> >
>
> Please note that the mdio-level delay properties are not the same as
> the ones on the PHY levels.
>
> reset-delay-us - this is the delay BEFORE *DEASSERTING* the reset line
> reset-post-delay-us - this is the delay AFTER *DEASSERTING* the reset line
>
> On PHY level we have:
>
> reset-assert-us - AFTER *ASSERTING*
> reset-deassert-us - AFTER *DEASSERTING*
>
> There never has been any reset-assert delay on that line before. It
> doesn't look like we need a delay BEFORE deasserting the line, do we?
>
The MDIO reset-delay-us happens "before deassert"/"after assert", so to
make things a proper move here I think it needs a resrt-assert, otherwise
behavior with respect to reset timing is definitely changed from this
patch!
Here's a trimmed version of the reset handling in mdio_bus.c to back
that up:
/* assert bus level PHY GPIO reset */
gpiod = devm_gpiod_get_optional(&bus->dev, "reset", GPIOD_OUT_HIGH);
...
} else if (gpiod) {
bus->reset_gpiod = gpiod;
fsleep(bus->reset_delay_us);
gpiod_set_value_cansleep(gpiod, 0);
if (bus->reset_post_delay_us > 0)
fsleep(bus->reset_post_delay_us);
}
so its assert reset, sleep reset_delay_us, deassert, sleep
reset_post_delay_us for the MDIO case.
Thanks,
Andrew
> I've been trying to make sure I view devicetree properties as an OS > agnostic ABI lately, with that in mind... > > The dt-binding says this for ethernet-phy: > > reset-assert-us: > description: > Delay after the reset was asserted in microseconds. If this > property is missing the delay will be skipped. > > If the hardware needs a delay I think we should encode it based on that > description, else we risk it starting to look like a unit impulse! I checked, and the documentation does appear correct, there is no default value. So yes, it does seem prudent to specify a value, otherwise it could be a short pulse. Andrew
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