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    SubjectRe: [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@codeaurora.org>
    > Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.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

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