linux-kernel - Re: [PATCH 3/3] arm64: dts: qcom: sdm845-mtp: Specify UFS device-reset GPIO

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Date:   Tue, 04 Jun 2019 09:22:42 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Pedro Sousa <pedrom.sousa@...opsys.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-arm-msm@...r.kernel.org, linux-gpio@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org, Evan Green <evgreen@...omium.org>
Subject: Re: [PATCH 3/3] arm64: dts: qcom: sdm845-mtp: Specify UFS device-reset GPIO

Quoting Bjorn Andersson (2019-06-04 00:20:01)
> Specify the UFS device-reset gpio, so that the controller will issue a
> reset of the UFS device.
> 
> Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> ---
>  arch/arm64/boot/dts/qcom/sdm845-mtp.dts | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/qcom/sdm845-mtp.dts b/arch/arm64/boot/dts/qcom/sdm845-mtp.dts
> index 2e78638eb73b..d116a0956a9c 100644
> --- a/arch/arm64/boot/dts/qcom/sdm845-mtp.dts
> +++ b/arch/arm64/boot/dts/qcom/sdm845-mtp.dts
> @@ -388,6 +388,8 @@
>  &ufs_mem_hc {
>         status = "okay";
>  
> +       device-reset-gpios = <&tlmm 150 GPIO_ACTIVE_LOW>;
> +

We had to do something similar on one particular brand of UFS that we had. I
think it was an SK Hynix part that had trouble and wouldn't provision properly.
Either way, we did this with a pinctrl toggle in the DTS where the "init" state
has the UFS_RESET pin asserted and then "default" state has the pin deasserted.
That was good enough to make this work.

	&ufs_mem_hc {
		pinctrl-names = "init", "default";
		pinctrl-0 = <&ufs_dev_reset_assert>;
		pinctrl-1 = <&ufs_dev_reset_deassert>;
	};

        ufs_dev_reset_assert: ufs_dev_reset_assert {
                config {
                        pins = "ufs_reset";
                        bias-pull-down;         /* default: pull down */
                        drive-strength = <8>;   /* default: 3.1 mA */
                        output-low; /* active low reset */
                };
        };

        ufs_dev_reset_deassert: ufs_dev_reset_deassert {
                config {
                        pins = "ufs_reset";
                        bias-pull-down;         /* default: pull down */
                        drive-strength = <8>;
                        output-high; /* active low reset */
                };
        };