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Date: Mon, 21 Oct 2019 12:58:51 -0700
From: Matthias Kaehlcke <mka@...omium.org>
To: Jeffrey Hugo <jeffrey.l.hugo@...il.com>
Cc: agross@...nel.org, bjorn.andersson@...aro.org,
linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] arm64: dts: qcom: msm8998: Fixup uart3 gpio config
for bluetooth
On Mon, Oct 21, 2019 at 09:19:21AM -0700, Jeffrey Hugo wrote:
> It turns out that the wcn3990 can float the gpio lines during bootup, etc
> which will result in the uart core thinking there is incoming data. This
> results in the bluetooth stack getting garbage. By applying a bias to
> match what wcn3990 would drive, the issue is corrected.
>
> Signed-off-by: Jeffrey Hugo <jeffrey.l.hugo@...il.com>
> ---
>
> v2:
> -split out pinctrl config by pin
>
> .../boot/dts/qcom/msm8998-clamshell.dtsi | 22 ++++++++++++++++
> arch/arm64/boot/dts/qcom/msm8998-mtp.dtsi | 22 ++++++++++++++++
> arch/arm64/boot/dts/qcom/msm8998-pins.dtsi | 25 ++++++++++++++++---
> 3 files changed, 65 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/boot/dts/qcom/msm8998-clamshell.dtsi b/arch/arm64/boot/dts/qcom/msm8998-clamshell.dtsi
> index 38a1c2ba5e83..8c9a3e0f3843 100644
> --- a/arch/arm64/boot/dts/qcom/msm8998-clamshell.dtsi
> +++ b/arch/arm64/boot/dts/qcom/msm8998-clamshell.dtsi
> @@ -37,6 +37,28 @@
> };
> };
>
> +&blsp1_uart3_on {
> + rx {
> + /delete-property/ bias-disable;
> + /*
> + * Configure a pull-up on 45 (RX). This is needed to
> + * avoid garbage data when the TX pin of the Bluetooth
> + * module is in tri-state (module powered off or not
> + * driving the signal yet).
> + */
> + bias-pull-up;
> + };
> +
> + cts {
> + /delete-property/ bias-disable;
> + /*
> + * Configure a pull-down on 47 (CTS) to match the pull
> + * of the Bluetooth module.
> + */
> + bias-pull-down;
> + };
> +};
> +
> &qusb2phy {
> status = "okay";
>
> diff --git a/arch/arm64/boot/dts/qcom/msm8998-mtp.dtsi b/arch/arm64/boot/dts/qcom/msm8998-mtp.dtsi
> index 8adb4969baec..74c14f50b0f6 100644
> --- a/arch/arm64/boot/dts/qcom/msm8998-mtp.dtsi
> +++ b/arch/arm64/boot/dts/qcom/msm8998-mtp.dtsi
> @@ -37,6 +37,28 @@
> };
> };
>
> +&blsp1_uart3_on {
> + rx {
> + /delete-property/ bias-disable;
> + /*
> + * Configure a pull-up on 45 (RX). This is needed to
> + * avoid garbage data when the TX pin of the Bluetooth
> + * module is in tri-state (module powered off or not
> + * driving the signal yet).
> + */
> + bias-pull-up;
> + };
> +
> + cts {
> + /delete-property/ bias-disable;
> + /*
> + * Configure a pull-down on 47 (CTS) to match the pull
> + * of the Bluetooth module.
> + */
> + bias-pull-down;
> + };
> +};
> +
> &blsp2_uart1 {
> status = "okay";
> };
> diff --git a/arch/arm64/boot/dts/qcom/msm8998-pins.dtsi b/arch/arm64/boot/dts/qcom/msm8998-pins.dtsi
> index e32d3ab395ea..7c222cbf19d9 100644
> --- a/arch/arm64/boot/dts/qcom/msm8998-pins.dtsi
> +++ b/arch/arm64/boot/dts/qcom/msm8998-pins.dtsi
> @@ -77,13 +77,30 @@
> };
>
> blsp1_uart3_on: blsp1_uart3_on {
> - mux {
> - pins = "gpio45", "gpio46", "gpio47", "gpio48";
> + tx {
> + pins = "gpio45";
> function = "blsp_uart3_a";
> + drive-strength = <2>;
Should the drive-strength really be configured in the .dtsi
of the SoC? I think of it as a board specific property, since it
depends on what is on the other end of the UART.
> + bias-disable;
This seems reasonable since the SoC drives the TX pin.
> };
>
> - config {
> - pins = "gpio45", "gpio46", "gpio47", "gpio48";
> + rx {
> + pins = "gpio46";
> + function = "blsp_uart3_a";
> + drive-strength = <2>;
'drive-strength' shouldn't be needed for an input pin
> + bias-disable;
In case of the input pins I'm not sure if this should/needs to be in
the .dtsi of the SoC. If it isn't really needed it would allow to
remove the '/delete-property/ bias-disable;' entries in the board
files.
> + };
> +
> + cts {
> + pins = "gpio47";
> + function = "blsp_uart3_a";
> + drive-strength = <2>;
'drive-strength' shouldn't be needed for an input pin
> + bias-disable;
> + };
> +
> + rfr {
> + pins = "gpio48";
> + function = "blsp_uart3_a";
> drive-strength = <2>;
> bias-disable;
> };
> --
> 2.17.1
>
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