[PATCH] arm64: dts: renesas: beacon: Fix i2c2 speed calcuation

[PATCH] arm64: dts: renesas: beacon: Fix i2c2 speed calcuation

[Adam Ford]

The desired i2c2 speed is 400KHz, but when measured on a scope, it
is incorrect.  The driver can use the i2c-scl-rising-time-ns to help
calculate the proper setting to get exactly 400KHz.

Fixes: 900d9fc3bece ("arm64: dts: renesas: beacon: Correct I2C bus speeds")
Signed-off-by: Adam Ford <aford173@gmail.com>

diff --git a/arch/arm64/boot/dts/renesas/beacon-renesom-baseboard.dtsi b/arch/arm64/boot/dts/renesas/beacon-renesom-baseboard.dtsi
index 2692cc64bff6..987357c58390 100644
--- a/arch/arm64/boot/dts/renesas/beacon-renesom-baseboard.dtsi
+++ b/arch/arm64/boot/dts/renesas/beacon-renesom-baseboard.dtsi
@@ -328,6 +328,7 @@ &hsusb {
 &i2c2 {
 	status = "okay";
 	clock-frequency = <400000>;
+	i2c-scl-rising-time-ns = <50>;
 	pinctrl-0 = <&i2c2_pins>;
 	pinctrl-names = "default";
 
-- 
2.25.1

Re: [PATCH] arm64: dts: renesas: beacon: Fix i2c2 speed calcuation

[Geert Uytterhoeven]

CC Wolfram

On Wed, Aug 25, 2021 at 2:28 PM Adam Ford <aford173@gmail.com> wrote:
> The desired i2c2 speed is 400KHz, but when measured on a scope, it
> is incorrect.  The driver can use the i2c-scl-rising-time-ns to help
> calculate the proper setting to get exactly 400KHz.
>
> Fixes: 900d9fc3bece ("arm64: dts: renesas: beacon: Correct I2C bus speeds")
> Signed-off-by: Adam Ford <aford173@gmail.com>
>
> diff --git a/arch/arm64/boot/dts/renesas/beacon-renesom-baseboard.dtsi b/arch/arm64/boot/dts/renesas/beacon-renesom-baseboard.dtsi
> index 2692cc64bff6..987357c58390 100644
> --- a/arch/arm64/boot/dts/renesas/beacon-renesom-baseboard.dtsi
> +++ b/arch/arm64/boot/dts/renesas/beacon-renesom-baseboard.dtsi
> @@ -328,6 +328,7 @@ &hsusb {
>  &i2c2 {
>         status = "okay";
>         clock-frequency = <400000>;
> +       i2c-scl-rising-time-ns = <50>;
>         pinctrl-0 = <&i2c2_pins>;
>         pinctrl-names = "default";
>
> --
> 2.25.1

Re: [PATCH] arm64: dts: renesas: beacon: Fix i2c2 speed calcuation

[Wolfram Sang]

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On Wed, Aug 25, 2021 at 02:47:21PM +0200, Geert Uytterhoeven wrote:
> CC Wolfram
> 
> On Wed, Aug 25, 2021 at 2:28 PM Adam Ford <aford173@gmail.com> wrote:
> > The desired i2c2 speed is 400KHz, but when measured on a scope, it
> > is incorrect.  The driver can use the i2c-scl-rising-time-ns to help
> > calculate the proper setting to get exactly 400KHz.

The question for me is: Has it been measured that SCL rising time is
really 50ns or has it been measured that the bus clock is now exactly
400kHz?


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Re: [PATCH] arm64: dts: renesas: beacon: Fix i2c2 speed calcuation

[Adam Ford]

On Tue, Sep 14, 2021 at 5:41 AM Wolfram Sang
<wsa+renesas@sang-engineering.com> wrote:
>
> On Wed, Aug 25, 2021 at 02:47:21PM +0200, Geert Uytterhoeven wrote:
> > CC Wolfram
> >
> > On Wed, Aug 25, 2021 at 2:28 PM Adam Ford <aford173@gmail.com> wrote:
> > > The desired i2c2 speed is 400KHz, but when measured on a scope, it
> > > is incorrect.  The driver can use the i2c-scl-rising-time-ns to help
> > > calculate the proper setting to get exactly 400KHz.
>
> The question for me is: Has it been measured that SCL rising time is
> really 50ns or has it been measured that the bus clock is now exactly
> 400kHz?

The person who originally reported this to me moved on, so I don't
know if he measured both the rise time or just the clock speed.  I
know originally, the clock speed was measured to be 426KHz instead of
400KHz, and with the change to the rise time, the measured clock speed
was exactly 400KHz.  I do not know if the measured rise time is really
50ns or not.

adam


>