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Message-ID: <e69c4a70-5b50-a1d3-f972-534255cbb2b4@quicinc.com>
Date: Wed, 11 Jan 2023 15:09:35 +0530
From: Sibi Sankar <quic_sibis@...cinc.com>
To: Bjorn Andersson <andersson@...nel.org>
CC: <agross@...nel.org>, <linux-arm-msm@...r.kernel.org>,
<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<krzysztof.kozlowski+dt@...aro.org>, <robh+dt@...nel.org>,
<konrad.dybcio@...ainline.org>, <robimarko@...il.com>,
<quic_gurus@...cinc.com>
Subject: Re: [PATCH V7 2/2] firmware: qcom: scm: Add wait-queue handling logic
Hey Bjorn,
Thanks for taking time to review the series.
On 1/10/23 23:37, Bjorn Andersson wrote:
> On Tue, Jan 10, 2023 at 12:07:45PM +0530, Sibi Sankar wrote:
>> From: Guru Das Srinagesh <quic_gurus@...cinc.com>
>>
>> When the firmware (FW) supports multiple requests per VM, multiple requests
>> from the same/different VM can reach the firmware at the same time. Since
>> the firmware currently being used has limited resources, it guards them
>> with a resource lock and puts requests on a wait-queue internally and
>> signals to HLOS that it is doing so. It does this by returning a new return
>> value in addition to success or error: SCM_WAITQ_SLEEP. A sleeping SCM call
>> can be woken up by an interrupt that the FW raises.
>>
>> 1) SCM_WAITQ_SLEEP:
>>
>> When an SCM call receives this return value instead of success
>> or error, FW has placed this call on a wait-queue and has signalled
>> HLOS to put it to non-interruptible sleep.
>>
>> Along with this return value, FW also passes to HLOS `wq_ctx` -
>> a unique number (UID) identifying the wait-queue that it has put
>> the call on, internally. This is to help HLOS with its own
>> bookkeeping to wake this sleeping call later.
>>
>> Additionally, FW also passes to HLOS `smc_call_ctx` - a UID
>> identifying the SCM call thus being put to sleep. This is also
>> for HLOS' bookkeeping to wake this call up later.
>>
>> These two additional values are passed via the a1 and a2
>> registers.
>>
>> N.B.: The "ctx" in the above UID names = "context".
>>
>> The handshake mechanism that HLOS uses to talk to FW about wait-queue
>> operations involves two new SMC calls.
>>
>> 1) get_wq_ctx():
>>
>> Arguments: None
>> Returns: wq_ctx, flags, more_pending
>>
>> Get the wait-queue context, and wake up either one or all of the
>> sleeping SCM calls associated with that wait-queue.
>>
>> Additionally, repeat this if there are more wait-queues that are
>> ready to have their requests woken up (`more_pending`).
>>
>> 2) wq_resume(smc_call_ctx):
>>
>> Arguments: smc_call_ctx
>>
>> HLOS needs to issue this in response to receiving an
>> IRQ, passing to FW the same smc_call_ctx that FW
>> receives from HLOS via the get_wq_ctx() call.
>>
>> (The mechanism to wake a SMC call back up is described in detail below)
>>
>> VM_1 VM_2 Firmware
>> │ │ │
>> │ │ │
>> │ │ │
>> │ │ │
>> │ REQUEST_1 │ │
>> ├────────────────────────┼─────────────────────────────────┤
>> │ │ │
>> │ │ ┌──┼──┐
>> │ │ │ │ │
>> │ │ REQUEST_2 │ │ │
>> │ ├──────────────────────────────┼──┤ │
>> │ │ │ │ │Resource
>> │ │ │ │ │is busy
>> │ │ {WQ_SLEEP} │ │ │
>> │ │◄─────────────────────────────┼──┤ │
>> │ │ wq_ctx, smc_call_ctx │ │ │
>> │ │ └──┼──┘
>> │ REQUEST_1 COMPLETE │ │
>> │◄───────────────────────┼─────────────────────────────────┤
>> │ │ │
>> │ │ IRQ │
>> │ │◄─-------------------------------│
>> │ │ │
>> │ │ get_wq_ctx() │
>> │ ├────────────────────────────────►│
>> │ │ │
>> │ │ │
>> │ │◄────────────────────────────────┤
>> │ │ wq_ctx, flags, and │
>> │ │ more_pending │
>> │ │ │
>> │ │ │
>> │ │ wq_resume(smc_call_ctx) │
>> │ ├────────────────────────────────►│
>> │ │ │
>> │ │ │
>> │ │ REQUEST_2 COMPLETE │
>> │ │◄────────────────────────────────┤
>> │ │ │
>> │ │ │
>>
>> With the exception of get_wq_ctx(), the other SMC call wq_resume() can
>> return WQ_SLEEP (these nested rounds of WQ_SLEEP are not shown in the
>> above diagram for the sake of simplicity). Therefore, introduce a new
>> do-while loop to handle multiple WQ_SLEEP return values for the same
>> parent SCM call.
>>
>> Request Completion in the above diagram refers to either a success
>> return value (zero) or error (and not SMC_WAITQ_SLEEP)
>>
>> Also add the interrupt handler that wakes up a sleeping SCM call.
>>
>> Signed-off-by: Guru Das Srinagesh <quic_gurus@...cinc.com>
>> Co-developed-by: Sibi Sankar <quic_sibis@...cinc.com>
>> Signed-off-by: Sibi Sankar <quic_sibis@...cinc.com>
>> ---
>>
>> v7:
>> - Move lookup + wait_for_completion into a single function in qcom_scm [Bjorn]
>> - Simplify completion retrieval [Bjorn]
>>
>> v6:
>> - Fix misc. nits in the scm driver [Krzysztof]
>>
>> v5:
>> - Handle the wake_one/wake_all flags [Guru]
>> - Rename flag handler to qcom_scm_waitq_wakeup [Bjorn]
>> - Resume scm call can return ebusy as well handle that scenario by retrying
>> the original smc call and not the resume call
>>
>> v4:
>> - platform_set_drvdata will be used by __scm_smc_do_quirk_handle_waitq to
>> get access to scm struct from device so retain it
>> - Use a single completion as it satisfies all of the current usecases [Bjorn]
>> - Inline scm_get_wq_ctx [Bjorn]
>> - Convert all pr_err to dev_err [Bjorn]
>> - Handle idr_destroy in a thread safe manner [Bjorn]
>> - Misc. Style fixes [Bjorn]
>>
>> v3:
>> - Fixup irq handling so as not to affect SoCs without the interrupt.
>> - Fix warnings reported by kernel test-bot.
>>
>> drivers/firmware/qcom_scm-smc.c | 90 ++++++++++++++++++++++++++++++---
>> drivers/firmware/qcom_scm.c | 89 +++++++++++++++++++++++++++++++-
>> drivers/firmware/qcom_scm.h | 8 +++
>> 3 files changed, 179 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/firmware/qcom_scm-smc.c b/drivers/firmware/qcom_scm-smc.c
>> index d111833364ba..30999f04749c 100644
>> --- a/drivers/firmware/qcom_scm-smc.c
>> +++ b/drivers/firmware/qcom_scm-smc.c
>> @@ -52,29 +52,101 @@ static void __scm_smc_do_quirk(const struct arm_smccc_args *smc,
>> } while (res->a0 == QCOM_SCM_INTERRUPTED);
>> }
>>
>> -static void __scm_smc_do(const struct arm_smccc_args *smc,
>> - struct arm_smccc_res *res, bool atomic)
>> +static void fill_wq_resume_args(struct arm_smccc_args *resume, u32 smc_call_ctx)
>> {
>> - int retry_count = 0;
>> + memset(resume->args, 0, sizeof(resume->args[0]) * ARRAY_SIZE(resume->args));
>> +
>> + resume->args[0] = ARM_SMCCC_CALL_VAL(ARM_SMCCC_STD_CALL,
>> + ARM_SMCCC_SMC_64, ARM_SMCCC_OWNER_SIP,
>> + SCM_SMC_FNID(QCOM_SCM_SVC_WAITQ, QCOM_SCM_WAITQ_RESUME));
>> +
>> + resume->args[1] = QCOM_SCM_ARGS(1);
>> +
>> + resume->args[2] = smc_call_ctx;
>> +}
>> +
>> +int scm_get_wq_ctx(u32 *wq_ctx, u32 *flags, u32 *more_pending)
>> +{
>> + int ret;
>> + struct arm_smccc_args get_wq_ctx = {0};
>> + struct arm_smccc_res get_wq_res;
>> +
>> + get_wq_ctx.args[0] = ARM_SMCCC_CALL_VAL(ARM_SMCCC_STD_CALL,
>> + ARM_SMCCC_SMC_64, ARM_SMCCC_OWNER_SIP,
>> + SCM_SMC_FNID(QCOM_SCM_SVC_WAITQ, QCOM_SCM_WAITQ_GET_WQ_CTX));
>> +
>> + /* Guaranteed to return only success or error, no WAITQ_* */
>> + __scm_smc_do_quirk(&get_wq_ctx, &get_wq_res);
>> + ret = get_wq_res.a0;
>> + if (ret)
>> + return ret;
>> +
>> + *wq_ctx = get_wq_res.a1;
>> + *flags = get_wq_res.a2;
>> + *more_pending = get_wq_res.a3;
>> +
>> + return 0;
>> +}
>> +
>> +static int __scm_smc_do_quirk_handle_waitq(struct device *dev, struct arm_smccc_args *waitq,
>> + struct arm_smccc_res *res)
>> +{
>> + int ret;
>> + struct arm_smccc_args resume;
>> + u32 wq_ctx, smc_call_ctx, flags;
>> + struct arm_smccc_args *smc = waitq;
>> +
>> + do {
>> + __scm_smc_do_quirk(smc, res);
>> +
>> + if (res->a0 == QCOM_SCM_WAITQ_SLEEP) {
>> + wq_ctx = res->a1;
>> + smc_call_ctx = res->a2;
>> + flags = res->a3;
>> +
>> + if (!dev)
>> + return -EPROBE_DEFER;
>> +
>> + ret = qcom_scm_lookup_completion(wq_ctx);
>> + if (ret)
>> + return ret;
>> +
>> + fill_wq_resume_args(&resume, smc_call_ctx);
>> + smc = &resume;
>> + }
>> + } while (res->a0 == QCOM_SCM_WAITQ_SLEEP);
>> +
>> + return 0;
>> +}
>> +
>> +static int __scm_smc_do(struct device *dev, struct arm_smccc_args *smc,
>> + struct arm_smccc_res *res, bool atomic)
>> +{
>> + int ret, retry_count = 0;
>>
>> if (atomic) {
>> __scm_smc_do_quirk(smc, res);
>> - return;
>> + return 0;
>> }
>>
>> do {
>> mutex_lock(&qcom_scm_lock);
>>
>> - __scm_smc_do_quirk(smc, res);
>> + ret = __scm_smc_do_quirk_handle_waitq(dev, smc, res);
>>
>> mutex_unlock(&qcom_scm_lock);
>>
>> + if (ret)
>> + return ret;
>> +
>> 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);
>> +
>> + return 0;
>> }
>>
>>
>> @@ -83,7 +155,7 @@ int __scm_smc_call(struct device *dev, const struct qcom_scm_desc *desc,
>> struct qcom_scm_res *res, bool atomic)
>> {
>> int arglen = desc->arginfo & 0xf;
>> - int i;
>> + int i, ret;
>> dma_addr_t args_phys = 0;
>> void *args_virt = NULL;
>> size_t alloc_len;
>> @@ -135,13 +207,17 @@ int __scm_smc_call(struct device *dev, const struct qcom_scm_desc *desc,
>> smc.args[SCM_SMC_LAST_REG_IDX] = args_phys;
>> }
>>
>> - __scm_smc_do(&smc, &smc_res, atomic);
>> + /* ret error check follows after args_virt cleanup*/
>> + ret = __scm_smc_do(dev, &smc, &smc_res, atomic);
>>
>> if (args_virt) {
>> dma_unmap_single(dev, args_phys, alloc_len, DMA_TO_DEVICE);
>> kfree(args_virt);
>> }
>>
>> + if (ret)
>> + return ret;
>> +
>> if (res) {
>> res->result[0] = smc_res.a1;
>> res->result[1] = smc_res.a2;
>> diff --git a/drivers/firmware/qcom_scm.c b/drivers/firmware/qcom_scm.c
>> index cdbfe54c8146..19ac506a9b1f 100644
>> --- a/drivers/firmware/qcom_scm.c
>> +++ b/drivers/firmware/qcom_scm.c
>> @@ -4,6 +4,7 @@
>> */
>> #include <linux/platform_device.h>
>> #include <linux/init.h>
>> +#include <linux/interrupt.h>
>> #include <linux/cpumask.h>
>> #include <linux/export.h>
>> #include <linux/dma-mapping.h>
>> @@ -13,6 +14,7 @@
>> #include <linux/qcom_scm.h>
>> #include <linux/of.h>
>> #include <linux/of_address.h>
>> +#include <linux/of_irq.h>
>> #include <linux/of_platform.h>
>> #include <linux/clk.h>
>> #include <linux/reset-controller.h>
>> @@ -33,6 +35,7 @@ struct qcom_scm {
>> struct clk *iface_clk;
>> struct clk *bus_clk;
>> struct icc_path *path;
>> + struct completion waitq_comp;
>> struct reset_controller_dev reset;
>>
>> /* control access to the interconnect path */
>> @@ -63,6 +66,9 @@ static const u8 qcom_scm_cpu_warm_bits[QCOM_SCM_BOOT_MAX_CPUS] = {
>> BIT(2), BIT(1), BIT(4), BIT(6)
>> };
>>
>> +#define QCOM_SMC_WAITQ_FLAG_WAKE_ONE BIT(0)
>> +#define QCOM_SMC_WAITQ_FLAG_WAKE_ALL BIT(1)
>> +
>> static const char * const qcom_scm_convention_names[] = {
>> [SMC_CONVENTION_UNKNOWN] = "unknown",
>> [SMC_CONVENTION_ARM_32] = "smc arm 32",
>> @@ -1325,11 +1331,79 @@ bool qcom_scm_is_available(void)
>> }
>> EXPORT_SYMBOL(qcom_scm_is_available);
>>
>> +static struct completion *qcom_scm_lookup_wq(struct qcom_scm *scm, u32 wq_ctx)
>
> This could either be seen as a remnant of the older versions of this
> patch, or a signalling of "place implementation here". I dislike both...
>
> Please rename it qcom_scm_assert_valid_wq_ctx() and just reference
> &scm->waitq_comp directly in the two places below.
ack
>
>> +{
>> + /* assert wq_ctx is zero */
>> + if (wq_ctx != 0) {
>> + dev_err(scm->dev, "No waitqueue found for wq_ctx %d\n", wq_ctx);
>
> I think you should be more specific here, perhaps:
>
> "Firmware unexpectedly passed non-zero wq_ctx\n"
>
> And then as suggested a comment stating what needs to be done when that
> happens.
ack
>
>> + return ERR_PTR(-EINVAL);
>> + }
>> +
>> + return &scm->waitq_comp;
>> +}
>> +
>> +int qcom_scm_lookup_completion(u32 wq_ctx)
>> +{
>> + struct completion *wq = NULL;
>
> You assign it on the very next line, no need to do so here.
I'll just reference it directly from the scm struct.
>
>> +
>> + wq = qcom_scm_lookup_wq(__scm, wq_ctx);
>> + if (IS_ERR(wq))
>> + return PTR_ERR(wq);
>> +
>> + wait_for_completion(wq);
>> +
>> + return 0;
>> +}
>> +
>> +static int qcom_scm_waitq_wakeup(struct qcom_scm *scm, unsigned int wq_ctx, bool wake_all)
>> +{
>> + struct completion *wq_to_wake;
>
> "wq" would be sufficient.
I'll just reference it directly from the scm struct.
>
> Thanks,
> Bjorn
>
>> +
>> + wq_to_wake = qcom_scm_lookup_wq(scm, wq_ctx);
>> + if (IS_ERR(wq_to_wake))
>> + return PTR_ERR(wq_to_wake);
>> +
>> + if (wake_all)
>> + complete_all(wq_to_wake);
>> + else
>> + complete(wq_to_wake);
>> +
>> + return 0;
>> +}
>> +
>> +static irqreturn_t qcom_scm_irq_handler(int irq, void *data)
>> +{
>> + int ret;
>> + struct qcom_scm *scm = data;
>> + u32 wq_ctx, flags, more_pending = 0;
>> +
>> + do {
>> + ret = scm_get_wq_ctx(&wq_ctx, &flags, &more_pending);
>> + if (ret) {
>> + dev_err(scm->dev, "GET_WQ_CTX SMC call failed: %d\n", ret);
>> + goto out;
>> + }
>> +
>> + if (flags != QCOM_SMC_WAITQ_FLAG_WAKE_ONE &&
>> + flags != QCOM_SMC_WAITQ_FLAG_WAKE_ALL) {
>> + dev_err(scm->dev, "Invalid flags found for wq_ctx: %u\n", flags);
>> + goto out;
>> + }
>> +
>> + ret = qcom_scm_waitq_wakeup(scm, wq_ctx, !!(flags & QCOM_SMC_WAITQ_FLAG_WAKE_ALL));
>> + if (ret)
>> + goto out;
>> + } while (more_pending);
>> +
>> +out:
>> + return IRQ_HANDLED;
>> +}
>> +
>> static int qcom_scm_probe(struct platform_device *pdev)
>> {
>> struct qcom_scm *scm;
>> unsigned long clks;
>> - int ret;
>> + int irq, ret;
>>
>> scm = devm_kzalloc(&pdev->dev, sizeof(*scm), GFP_KERNEL);
>> if (!scm)
>> @@ -1402,6 +1476,19 @@ static int qcom_scm_probe(struct platform_device *pdev)
>> __scm = scm;
>> __scm->dev = &pdev->dev;
>>
>> + init_completion(&__scm->waitq_comp);
>> +
>> + irq = platform_get_irq(pdev, 0);
>> + if (irq < 0) {
>> + if (irq != -ENXIO)
>> + return irq;
>> + } else {
>> + ret = devm_request_threaded_irq(__scm->dev, irq, NULL, qcom_scm_irq_handler,
>> + IRQF_ONESHOT, "qcom-scm", __scm);
>> + if (ret < 0)
>> + return dev_err_probe(scm->dev, ret, "Failed to request qcom-scm irq\n");
>> + }
>> +
>> __get_convention();
>>
>> /*
>> diff --git a/drivers/firmware/qcom_scm.h b/drivers/firmware/qcom_scm.h
>> index db3d08a01209..018e9867d55a 100644
>> --- a/drivers/firmware/qcom_scm.h
>> +++ b/drivers/firmware/qcom_scm.h
>> @@ -60,6 +60,9 @@ struct qcom_scm_res {
>> u64 result[MAX_QCOM_SCM_RETS];
>> };
>>
>> +int qcom_scm_lookup_completion(u32 wq_ctx);
I'll rename ^^ into qcom_scm_wait_for_wq_completion instead.
>> +int scm_get_wq_ctx(u32 *wq_ctx, u32 *flags, u32 *more_pending);
>> +
>> #define SCM_SMC_FNID(s, c) ((((s) & 0xFF) << 8) | ((c) & 0xFF))
>> extern int __scm_smc_call(struct device *dev, const struct qcom_scm_desc *desc,
>> enum qcom_scm_convention qcom_convention,
>> @@ -129,6 +132,10 @@ extern int scm_legacy_call(struct device *dev, const struct qcom_scm_desc *desc,
>> #define QCOM_SCM_SMMU_CONFIG_ERRATA1 0x03
>> #define QCOM_SCM_SMMU_CONFIG_ERRATA1_CLIENT_ALL 0x02
>>
>> +#define QCOM_SCM_SVC_WAITQ 0x24
>> +#define QCOM_SCM_WAITQ_RESUME 0x02
>> +#define QCOM_SCM_WAITQ_GET_WQ_CTX 0x03
>> +
>> /* common error codes */
>> #define QCOM_SCM_V2_EBUSY -12
>> #define QCOM_SCM_ENOMEM -5
>> @@ -137,6 +144,7 @@ extern int scm_legacy_call(struct device *dev, const struct qcom_scm_desc *desc,
>> #define QCOM_SCM_EINVAL_ARG -2
>> #define QCOM_SCM_ERROR -1
>> #define QCOM_SCM_INTERRUPTED 1
>> +#define QCOM_SCM_WAITQ_SLEEP 2
>>
>> static inline int qcom_scm_remap_error(int err)
>> {
>> --
>> 2.17.1
>>
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