linux-kernel - Re: [PATCH v3 1/4] firmware: qcom_scm-64: Add atomic version of qcom_scm

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Date:   Tue, 18 Jun 2019 18:55:36 +0100
From:   Will Deacon <will.deacon@....com>
To:     Vivek Gautam <vivek.gautam@...eaurora.org>
Cc:     agross@...nel.org, robh+dt@...nel.org, robin.murphy@....com,
        joro@...tes.org, bjorn.andersson@...aro.org,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        david.brown@...aro.org
Subject: Re: [PATCH v3 1/4] firmware: qcom_scm-64: Add atomic version of
 qcom_scm_call

On Wed, Jun 12, 2019 at 12:45:51PM +0530, Vivek Gautam wrote:
> There are scnenarios where drivers are required to make a
> scm call in atomic context, such as in one of the qcom's
> arm-smmu-500 errata [1].
> 
> [1] ("https://source.codeaurora.org/quic/la/kernel/msm-4.9/commit/
>       drivers/iommu/arm-smmu.c?h=CogSystems-msm-49/
>       msm-4.9&id=da765c6c75266b38191b38ef086274943f353ea7")
> 
> Signed-off-by: Vivek Gautam <vivek.gautam@...eaurora.org>
> Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> ---
>  drivers/firmware/qcom_scm-64.c | 136 ++++++++++++++++++++++++++++-------------
>  1 file changed, 92 insertions(+), 44 deletions(-)
> 
> diff --git a/drivers/firmware/qcom_scm-64.c b/drivers/firmware/qcom_scm-64.c
> index 91d5ad7cf58b..b6dca32c5ac4 100644
> --- a/drivers/firmware/qcom_scm-64.c
> +++ b/drivers/firmware/qcom_scm-64.c
> @@ -62,32 +62,71 @@ static DEFINE_MUTEX(qcom_scm_lock);
>  #define FIRST_EXT_ARG_IDX 3
>  #define N_REGISTER_ARGS (MAX_QCOM_SCM_ARGS - N_EXT_QCOM_SCM_ARGS + 1)
>  
> -/**
> - * qcom_scm_call() - Invoke a syscall in the secure world
> - * @dev:	device
> - * @svc_id:	service identifier
> - * @cmd_id:	command identifier
> - * @desc:	Descriptor structure containing arguments and return values
> - *
> - * Sends a command to the SCM and waits for the command to finish processing.
> - * This should *only* be called in pre-emptible context.
> -*/
> -static int qcom_scm_call(struct device *dev, u32 svc_id, u32 cmd_id,
> -			 const struct qcom_scm_desc *desc,
> -			 struct arm_smccc_res *res)
> +static void __qcom_scm_call_do(const struct qcom_scm_desc *desc,
> +			       struct arm_smccc_res *res, u32 fn_id,
> +			       u64 x5, u32 type)
> +{
> +	u64 cmd;
> +	struct arm_smccc_quirk quirk = {.id = ARM_SMCCC_QUIRK_QCOM_A6};
> +
> +	cmd = ARM_SMCCC_CALL_VAL(type, qcom_smccc_convention,
> +				 ARM_SMCCC_OWNER_SIP, fn_id);
> +
> +	quirk.state.a6 = 0;
> +
> +	do {
> +		arm_smccc_smc_quirk(cmd, desc->arginfo, desc->args[0],
> +				    desc->args[1], desc->args[2], x5,
> +				    quirk.state.a6, 0, res, &quirk);
> +
> +		if (res->a0 == QCOM_SCM_INTERRUPTED)
> +			cmd = res->a0;
> +
> +	} while (res->a0 == QCOM_SCM_INTERRUPTED);
> +}
> +
> +static void qcom_scm_call_do(const struct qcom_scm_desc *desc,
> +			     struct arm_smccc_res *res, u32 fn_id,
> +			     u64 x5, bool atomic)
> +{

Maybe pass in the call type (ARM_SMCCC_FAST_CALL vs ARM_SMCCC_STD_CALL)
instead of "bool atomic"? Would certainly make the callsites easier to
understand.

> +	int retry_count = 0;
> +
> +	if (!atomic) {
> +		do {
> +			mutex_lock(&qcom_scm_lock);
> +
> +			__qcom_scm_call_do(desc, res, fn_id, x5,
> +					   ARM_SMCCC_STD_CALL);
> +
> +			mutex_unlock(&qcom_scm_lock);
> +
> +			if (res->a0 == QCOM_SCM_V2_EBUSY) {
> +				if (retry_count++ > QCOM_SCM_EBUSY_MAX_RETRY)
> +					break;
> +				msleep(QCOM_SCM_EBUSY_WAIT_MS);
> +			}
> +		}  while (res->a0 == QCOM_SCM_V2_EBUSY);
> +	} else {
> +		__qcom_scm_call_do(desc, res, fn_id, x5, ARM_SMCCC_FAST_CALL);
> +	}

Is it safe to make concurrent FAST calls?

Will