[PATCH V10 0/2] SCM: Add support for wait-queue aware firmware

[PATCH V10 0/2] SCM: Add support for wait-queue aware firmware

[Sibi Sankar]

This patch series enables the QCOM SCM driver to support firmware (FW) versions
that expect the high-level OS (HLOS) to be tolerant of SCM call requests not
being processed right away and, instead, being placed on a wait-queue in FW and
processed accordingly.

The problem this feature is fixing is as follows. In a scenario where there is
a VM in addition to HLOS (and an underlying hypervisor):

1. HLOS makes an SMC call on core 5
2. The hypervisor scheduling interrupt interrupts this SMC call.
3. The hypervisor schedules the VM on core 5.
4. The VM makes an SMC call on core 5.
5. The SMC call is non-interruptibly stuck on FW spinlock on core 5.
6. HLOS cannot reschedule since core 5 is not responding to Reschedule IPIs.
7. Watchdog timer expires waiting for core 5.

This problem is solved by FW returning a new return code SCM_WAITQ_SLEEP to
HLOS right away when it is overwhelmed by the VM's SMC call. HLOS then places
the call on a wait-queue and wakes it up when it receives an interrupt that
signifies "all-clear".

There are two new SMC calls also being defined in this design that, together
with one new return code, form the handshake protocol between Linux and FW.

This design is also backwards-compatible with existing firmware versions that
do not support this feature.

V10:
- Drop unused flags variable in quirk_handle_waitq [kernel test bot]

V9:
- Drop unused complete_all [Srini]

v8:
- Rename qcom_scm_lookup_wq to qcom_scm_assert_valid_wq_ctx [Bjorn] 
- Document wq_ctx limitations [Guru]
- Drop dev check and add include completion header [Srini]
- Rename qcom_scm_lookup_completion to qcom_scm_wait_for_wq_completion.

v7:
- Move lookup + wait_for_completion into a single function in qcom_scm [Bjorn]
- Simplify completion retrieval [Bjorn]

v6:
- Fix subject of bindings [Krzysztof]
- Update commit message to include the SoC supporting the feature [Krzysztof]
- Make the interrupt property valid on SM8450 SoC [Krzysztof]
- Fix misc. nits in the scm driver [Krzysztof]
- Rebased on Krzysztof's narrow clocks and interconnect series.

v5:
- Pick up R-b
- 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]
- Qualify bindings [Krzysztoff]

v3:
- Drop allow-multi-call property since HLOS doesn't completely support it
  yet.
- Fixup irq handling so as not to affect SoCs without the interrupt.
- Fix warnings reported by kernel test-bot.

v2:
- Changes made to patches 4 and 5 are listed therein.
- Rebased dt-bindings on top of the YAML conversion patch [1].

Guru Das Srinagesh (2):
  dt-bindings: firmware: qcom,scm: Add optional interrupt
  firmware: qcom: scm: Add wait-queue handling logic

 .../bindings/firmware/qcom,scm.yaml           | 18 ++++
 drivers/firmware/qcom_scm-smc.c               | 86 ++++++++++++++++--
 drivers/firmware/qcom_scm.c                   | 90 ++++++++++++++++++-
 drivers/firmware/qcom_scm.h                   |  8 ++
 4 files changed, 194 insertions(+), 8 deletions(-)

-- 
2.17.1

[PATCH V10 1/2] dt-bindings: firmware: qcom,scm: Add optional interrupt

[Sibi Sankar]

From: Guru Das Srinagesh <quic_gurus@quicinc.com>

Add an interrupt specification to the bindings to support the wait-queue
feature on SM8450 SoCs.

Signed-off-by: Guru Das Srinagesh <quic_gurus@quicinc.com>
Signed-off-by: Sibi Sankar <quic_sibis@quicinc.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
---

The interrupt property for scm firmware from a binding perspective is
completely optional i.e. not all tz fw running in the wild on sm8450
devices support this feature. The bootloader does the interrupt property
addition on sm8450 devices with wait-queue support.

v7
- Pick up R-b.

v6:
- Fix subject of bindings [Krzysztof]
- Update commit message to include the SoC supporting the feature [Krzysztof]
- Make the interrupt property valid on SM8450 SoC [Krzysztof]
- Rebased on Krzysztof's narrow clocks and interconnect series.
- Drop R-b

v5:
- Pick up R-b

v4:

- Qualify bindings [Krzysztoff]

 .../devicetree/bindings/firmware/qcom,scm.yaml | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/Documentation/devicetree/bindings/firmware/qcom,scm.yaml b/Documentation/devicetree/bindings/firmware/qcom,scm.yaml
index 8e6e9ebb343d..01c861f36983 100644
--- a/Documentation/devicetree/bindings/firmware/qcom,scm.yaml
+++ b/Documentation/devicetree/bindings/firmware/qcom,scm.yaml
@@ -73,6 +73,12 @@ properties:
   '#reset-cells':
     const: 1
 
+  interrupts:
+    description:
+      The wait-queue interrupt that firmware raises as part of handshake
+      protocol to handle sleeping SCM calls.
+    maxItems: 1
+
   qcom,dload-mode:
     $ref: /schemas/types.yaml#/definitions/phandle-array
     items:
@@ -162,6 +168,18 @@ allOf:
       properties:
         interconnects: false
 
+  # Interrupts
+  - if:
+      not:
+        properties:
+          compatible:
+            contains:
+              enum:
+                - qcom,scm-sm8450
+    then:
+      properties:
+        interrupts: false
+
 required:
   - compatible
 
-- 
2.17.1

[PATCH V10 2/2] firmware: qcom: scm: Add wait-queue handling logic

[Sibi Sankar]

From: Guru Das Srinagesh <quic_gurus@quicinc.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@quicinc.com>
Co-developed-by: Sibi Sankar <quic_sibis@quicinc.com>
Signed-off-by: Sibi Sankar <quic_sibis@quicinc.com>
---

v10:
- Drop unused flags variable in quirk_handle_waitq [kernel test bot]

v9:
- Drop unused complete_all [Srini]

v8:
- Rename qcom_scm_lookup_wq to qcom_scm_assert_valid_wq_ctx [Bjorn] 
- Document wq_ctx limitations [Guru]
- Drop dev check and add include completion header [Srini]
- Rename qcom_scm_lookup_completion to qcom_scm_wait_for_wq_completion.

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 | 86 ++++++++++++++++++++++++++++---
 drivers/firmware/qcom_scm.c     | 90 ++++++++++++++++++++++++++++++++-
 drivers/firmware/qcom_scm.h     |  8 +++
 3 files changed, 176 insertions(+), 8 deletions(-)

diff --git a/drivers/firmware/qcom_scm-smc.c b/drivers/firmware/qcom_scm-smc.c
index d111833364ba..bb3235a64b8f 100644
--- a/drivers/firmware/qcom_scm-smc.c
+++ b/drivers/firmware/qcom_scm-smc.c
@@ -52,29 +52,97 @@ 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_res get_wq_res;
+	struct arm_smccc_args get_wq_ctx = {0};
+
+	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;
+	u32 wq_ctx, smc_call_ctx;
+	struct arm_smccc_args resume;
+	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;
+
+			ret = qcom_scm_wait_for_wq_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 +151,7 @@ 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 +203,17 @@ 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..2000323722bf 100644
--- a/drivers/firmware/qcom_scm.c
+++ b/drivers/firmware/qcom_scm.c
@@ -4,6 +4,8 @@
  */
 #include <linux/platform_device.h>
 #include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/completion.h>
 #include <linux/cpumask.h>
 #include <linux/export.h>
 #include <linux/dma-mapping.h>
@@ -13,6 +15,7 @@
 #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 +36,7 @@ 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 +67,9 @@ 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 +1332,79 @@ bool qcom_scm_is_available(void)
 }
 EXPORT_SYMBOL(qcom_scm_is_available);
 
+static int qcom_scm_assert_valid_wq_ctx(u32 wq_ctx)
+{
+	/* FW currently only supports a single wq_ctx (zero).
+	 * TODO: Update this logic to include dynamic allocation and lookup of
+	 * completion structs when FW supports more wq_ctx values.
+	 */
+	if (wq_ctx != 0) {
+		dev_err(__scm->dev, "Firmware unexpectedly passed non-zero wq_ctx\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+int qcom_scm_wait_for_wq_completion(u32 wq_ctx)
+{
+	int ret;
+
+	ret = qcom_scm_assert_valid_wq_ctx(wq_ctx);
+	if (ret)
+		return ret;
+
+	wait_for_completion(&__scm->waitq_comp);
+
+	return 0;
+}
+
+static int qcom_scm_waitq_wakeup(struct qcom_scm *scm, unsigned int wq_ctx)
+{
+	int ret;
+
+	ret = qcom_scm_assert_valid_wq_ctx(wq_ctx);
+	if (ret)
+		return ret;
+
+	complete(&__scm->waitq_comp);
+
+	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);
+		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 +1477,19 @@ 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..e6e512bd57d1 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_wait_for_wq_completion(u32 wq_ctx);
+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

Re: [PATCH V10 2/2] firmware: qcom: scm: Add wait-queue handling logic

[Guru Das Srinagesh]

On Jan 13 2023 21:41, Sibi Sankar wrote:
> From: Guru Das Srinagesh <quic_gurus@quicinc.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@quicinc.com>
> Co-developed-by: Sibi Sankar <quic_sibis@quicinc.com>
> Signed-off-by: Sibi Sankar <quic_sibis@quicinc.com>

Reviewed-by: Guru Das Srinagesh <quic_gurus@quicinc.com>

Thank you.

Guru Das.

Re: [PATCH V10 0/2] SCM: Add support for wait-queue aware firmware

[Bjorn Andersson]

On Fri, 13 Jan 2023 21:41:12 +0530, Sibi Sankar wrote:
> This patch series enables the QCOM SCM driver to support firmware (FW) versions
> that expect the high-level OS (HLOS) to be tolerant of SCM call requests not
> being processed right away and, instead, being placed on a wait-queue in FW and
> processed accordingly.
> 
> The problem this feature is fixing is as follows. In a scenario where there is
> a VM in addition to HLOS (and an underlying hypervisor):
> 
> [...]

Applied, thanks!

[1/2] dt-bindings: firmware: qcom,scm: Add optional interrupt
      commit: afb37e2577938bb854f20d428d8f29a01ea8bc93
[2/2] firmware: qcom: scm: Add wait-queue handling logic
      commit: 6bf32599223634294cdc6efb359ffaab1d68073c

Best regards,
-- 
Bjorn Andersson <andersson@kernel.org>