linux-kernel - Re: [PATCH] usb: phy: qusb: Use scm call to update value in register

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Message-ID: <20220915172118.q2bsjlfcau33z6pa@builder.lan>
Date:   Thu, 15 Sep 2022 12:21:18 -0500
From:   Bjorn Andersson <andersson@...nel.org>
To:     Hiren Gohel <quic_vhiren@...cinc.com>
Cc:     Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        linux-kernel@...r.kernel.org,
        Udipto Goswami <quic_ugoswami@...cinc.com>,
        Pratham Pratap <quic_ppratap@...cinc.com>,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH] usb: phy: qusb: Use scm call to update value in register

On Thu, Sep 15, 2022 at 07:17:07PM +0530, Hiren Gohel wrote:
> Registers used by vendors to control any functionality could be
> implemented by making the register secured. In such cases the
> register cannot be updated with a new value since the normal
> write ops will fail.
> 
> Hence, use the scm_call to do a secure write to the register.
> 

This looks reasonable, but we need a caller of this API in order to
merge this patch.

> Signed-off-by: Hiren Gohel <quic_vhiren@...cinc.com>
> ---
>  drivers/firmware/qcom_scm.c | 19 +++++++++++++++++++
>  drivers/firmware/qcom_scm.h |  1 +
>  include/linux/qcom_scm.h    |  2 ++
>  3 files changed, 22 insertions(+)
> 
> diff --git a/drivers/firmware/qcom_scm.c b/drivers/firmware/qcom_scm.c
> index cdbfe54..7131df8 100644
> --- a/drivers/firmware/qcom_scm.c
> +++ b/drivers/firmware/qcom_scm.c
> @@ -400,6 +400,25 @@ int qcom_scm_set_remote_state(u32 state, u32 id)
>  }
>  EXPORT_SYMBOL(qcom_scm_set_remote_state);
>  
> +void qcom_scm_phy_update_scm_level_shifter(u32 val)

That second "scm" doesn't seem necessary.

> +{
> +	int ret;
> +	struct qcom_scm_desc desc = {
> +		.svc = QCOM_SCM_SVC_BOOT,
> +		.cmd = QCOM_SCM_QUSB2PHY_LVL_SHIFTER_CMD_ID,
> +		.owner = ARM_SMCCC_OWNER_SIP
> +	};
> +
> +	desc.args[0] = val;
> +	desc.args[1] = 0;
> +	desc.arginfo = QCOM_SCM_ARGS(2);
> +
> +	ret = qcom_scm_call(__scm->dev, &desc, NULL);

Would it not make sense to return this error to the caller?

Regards,
Bjorn

> +	if (ret)
> +		pr_err("Failed to update scm level shifter=0x%x\n", ret);
> +}
> +EXPORT_SYMBOL(qcom_scm_phy_update_scm_level_shifter);
> +
>  static int __qcom_scm_set_dload_mode(struct device *dev, bool enable)
>  {
>  	struct qcom_scm_desc desc = {
> diff --git a/drivers/firmware/qcom_scm.h b/drivers/firmware/qcom_scm.h
> index 0d51eef..0a8c25b 100644
> --- a/drivers/firmware/qcom_scm.h
> +++ b/drivers/firmware/qcom_scm.h
> @@ -81,6 +81,7 @@ extern int scm_legacy_call(struct device *dev, const struct qcom_scm_desc *desc,
>  #define QCOM_SCM_BOOT_SET_ADDR_MC	0x11
>  #define QCOM_SCM_BOOT_SET_REMOTE_STATE	0x0a
>  #define QCOM_SCM_FLUSH_FLAG_MASK	0x3
> +#define QCOM_SCM_QUSB2PHY_LVL_SHIFTER_CMD_ID	0x1B
>  #define QCOM_SCM_BOOT_MAX_CPUS		4
>  #define QCOM_SCM_BOOT_MC_FLAG_AARCH64	BIT(0)
>  #define QCOM_SCM_BOOT_MC_FLAG_COLDBOOT	BIT(1)
> diff --git a/include/linux/qcom_scm.h b/include/linux/qcom_scm.h
> index f8335644..3e5cbe9 100644
> --- a/include/linux/qcom_scm.h
> +++ b/include/linux/qcom_scm.h
> @@ -124,4 +124,6 @@ extern int qcom_scm_lmh_dcvsh(u32 payload_fn, u32 payload_reg, u32 payload_val,
>  extern int qcom_scm_lmh_profile_change(u32 profile_id);
>  extern bool qcom_scm_lmh_dcvsh_available(void);
>  
> +extern void qcom_scm_phy_update_scm_level_shifter(u32 val);
> +
>  #endif
> -- 
> 2.7.4
>