[PATCH V6 0/2] SCM: Add support for wait-queue aware firmware

[PATCH V6 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.

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].

Depends on Krzysztof's narrow clocks and interconnect series:
https://patchwork.kernel.org/project/linux-arm-msm/patch/20221122092345.44369-1-krzysztof.kozlowski@linaro.org/
https://patchwork.kernel.org/project/linux-arm-msm/patch/20221122092345.44369-2-krzysztof.kozlowski@linaro.org/

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               |  97 +++++++++++++--
 drivers/firmware/qcom_scm.c                   | 114 +++++++++++++++++-
 drivers/firmware/qcom_scm.h                   |   9 ++
 4 files changed, 230 insertions(+), 8 deletions(-)

-- 
2.17.1

[PATCH V6 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>
---

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.

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 V6 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>
---

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 |  97 +++++++++++++++++++++++++--
 drivers/firmware/qcom_scm.c     | 114 +++++++++++++++++++++++++++++++-
 drivers/firmware/qcom_scm.h     |   9 +++
 3 files changed, 212 insertions(+), 8 deletions(-)

diff --git a/drivers/firmware/qcom_scm-smc.c b/drivers/firmware/qcom_scm-smc.c
index d111833364ba..385615d76e94 100644
--- a/drivers/firmware/qcom_scm-smc.c
+++ b/drivers/firmware/qcom_scm-smc.c
@@ -52,29 +52,108 @@ 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)
+{
+	struct qcom_scm *scm;
+	struct completion *wq = NULL;
+	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;
+
+			scm = dev_get_drvdata(dev);
+			wq = qcom_scm_lookup_wq(scm, wq_ctx);
+			if (IS_ERR_OR_NULL(wq)) {
+				dev_err(dev, "No waitqueue found for wq_ctx %d: %ld\n",
+					wq_ctx, PTR_ERR(wq));
+				return PTR_ERR(wq) ? : -EINVAL;
+			}
+
+			wait_for_completion(wq);
+			fill_wq_resume_args(&resume, smc_call_ctx);
+			smc = &resume;
+			wq = NULL;
+		}
+	} 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 +162,7 @@ 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 +214,17 @@ 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..89de6dd7567d 100644
--- a/drivers/firmware/qcom_scm.c
+++ b/drivers/firmware/qcom_scm.c
@@ -3,7 +3,9 @@
  * Copyright (C) 2015 Linaro Ltd.
  */
 #include <linux/platform_device.h>
+#include <linux/idr.h>
 #include <linux/init.h>
+#include <linux/interrupt.h>
 #include <linux/cpumask.h>
 #include <linux/export.h>
 #include <linux/dma-mapping.h>
@@ -13,9 +15,12 @@
 #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>
+#include <linux/spinlock.h>
+#include <linux/ktime.h>
 #include <linux/arm-smccc.h>
 
 #include "qcom_scm.h"
@@ -27,12 +32,20 @@ module_param(download_mode, bool, 0);
 #define SCM_HAS_IFACE_CLK	BIT(1)
 #define SCM_HAS_BUS_CLK		BIT(2)
 
+struct qcom_scm_waitq {
+	struct idr idr;
+	/* control access to IDR */
+	spinlock_t idr_lock;
+	struct completion waitq_comp;
+};
+
 struct qcom_scm {
 	struct device *dev;
 	struct clk *core_clk;
 	struct clk *iface_clk;
 	struct clk *bus_clk;
 	struct icc_path *path;
+	struct qcom_scm_waitq waitq;
 	struct reset_controller_dev reset;
 
 	/* control access to the interconnect path */
@@ -63,6 +76,9 @@ 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 +1341,82 @@ bool qcom_scm_is_available(void)
 }
 EXPORT_SYMBOL(qcom_scm_is_available);
 
+struct completion *qcom_scm_lookup_wq(struct qcom_scm *scm, u32 wq_ctx)
+{
+	int err;
+	unsigned long flags;
+	u32 wq_ctx_idr = wq_ctx;
+	struct completion *wq = NULL;
+
+	spin_lock_irqsave(&scm->waitq.idr_lock, flags);
+	wq = idr_find(&scm->waitq.idr, wq_ctx);
+	if (wq)
+		goto out;
+
+	wq = &scm->waitq.waitq_comp;
+
+	err = idr_alloc_u32(&scm->waitq.idr, wq, &wq_ctx_idr,
+			    U32_MAX, GFP_ATOMIC);
+	if (err < 0)
+		wq = ERR_PTR(err);
+
+out:
+	spin_unlock_irqrestore(&scm->waitq.idr_lock, flags);
+	return wq;
+}
+
+static int qcom_scm_waitq_wakeup(struct qcom_scm *scm, unsigned int wq_ctx, bool wake_all)
+{
+	struct completion *wq_to_wake;
+
+	wq_to_wake = qcom_scm_lookup_wq(scm, wq_ctx);
+	if (IS_ERR_OR_NULL(wq_to_wake)) {
+		dev_err(scm->dev, "No waitqueue found for wq_ctx %d: %ld\n",
+			wq_ctx, PTR_ERR(wq_to_wake));
+		return PTR_ERR(wq_to_wake) ? : -EINVAL;
+	}
+
+	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)
@@ -1399,9 +1486,28 @@ static int qcom_scm_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
+	platform_set_drvdata(pdev, scm);
+
 	__scm = scm;
 	__scm->dev = &pdev->dev;
 
+	spin_lock_init(&__scm->waitq.idr_lock);
+	idr_init(&__scm->waitq.idr);
+	init_completion(&__scm->waitq.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) {
+			idr_destroy(&__scm->waitq.idr);
+			return dev_err_probe(scm->dev, ret, "Failed to request qcom-scm irq\n");
+		}
+	}
+
 	__get_convention();
 
 	/*
@@ -1417,6 +1523,12 @@ static int qcom_scm_probe(struct platform_device *pdev)
 
 static void qcom_scm_shutdown(struct platform_device *pdev)
 {
+	unsigned long flags;
+
+	spin_lock_irqsave(&__scm->waitq.idr_lock, flags);
+	idr_destroy(&__scm->waitq.idr);
+	spin_unlock_irqrestore(&__scm->waitq.idr_lock, flags);
+
 	/* Clean shutdown, disable download mode to allow normal restart */
 	if (download_mode)
 		qcom_scm_set_download_mode(false);
diff --git a/drivers/firmware/qcom_scm.h b/drivers/firmware/qcom_scm.h
index db3d08a01209..d1e9e8269692 100644
--- a/drivers/firmware/qcom_scm.h
+++ b/drivers/firmware/qcom_scm.h
@@ -60,6 +60,10 @@ struct qcom_scm_res {
 	u64 result[MAX_QCOM_SCM_RETS];
 };
 
+struct qcom_scm;
+struct completion *qcom_scm_lookup_wq(struct qcom_scm *scm, 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 +133,10 @@ 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 +145,7 @@ 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 V6 1/2] dt-bindings: firmware: qcom,scm: Add optional interrupt

[Krzysztof Kozlowski]

On 08/12/2022 07:40, Sibi Sankar wrote:
> 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>
> ---
> 
> 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.


Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

Best regards,
Krzysztof

Re: [PATCH V6 2/2] firmware: qcom: scm: Add wait-queue handling logic

[Bjorn Andersson]

On Thu, Dec 08, 2022 at 12:10:31PM +0530, Sibi Sankar wrote:
> diff --git a/drivers/firmware/qcom_scm-smc.c b/drivers/firmware/qcom_scm-smc.c
[..]
> +static int __scm_smc_do_quirk_handle_waitq(struct device *dev, struct arm_smccc_args *waitq,
> +					   struct arm_smccc_res *res)
> +{
> +	struct qcom_scm *scm;
> +	struct completion *wq = NULL;
> +	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;
> +
> +			scm = dev_get_drvdata(dev);
> +			wq = qcom_scm_lookup_wq(scm, wq_ctx);
> +			if (IS_ERR_OR_NULL(wq)) {
> +				dev_err(dev, "No waitqueue found for wq_ctx %d: %ld\n",
> +					wq_ctx, PTR_ERR(wq));
> +				return PTR_ERR(wq) ? : -EINVAL;
> +			}
> +
> +			wait_for_completion(wq);

I think it would be cleaner to push the lookup + wait_for_completion
into a function in qcom_scm.c. Then you don't need to pull the drvdata
and you have the wq handling grouped in one place.

> +			fill_wq_resume_args(&resume, smc_call_ctx);
> +			smc = &resume;
> +			wq = NULL;
> +		}
> +	} while (res->a0 == QCOM_SCM_WAITQ_SLEEP);
> +
> +	return 0;
> +}
[..]
> diff --git a/drivers/firmware/qcom_scm.c b/drivers/firmware/qcom_scm.c
[..]
> +struct completion *qcom_scm_lookup_wq(struct qcom_scm *scm, u32 wq_ctx)
> +{
> +	int err;
> +	unsigned long flags;
> +	u32 wq_ctx_idr = wq_ctx;
> +	struct completion *wq = NULL;
> +
> +	spin_lock_irqsave(&scm->waitq.idr_lock, flags);
> +	wq = idr_find(&scm->waitq.idr, wq_ctx);
> +	if (wq)
> +		goto out;
> +
> +	wq = &scm->waitq.waitq_comp;

The idr here gives an impression of providing similar functionality as
in the previous post, but will actually always provide the same
completion. As such, if the firmware would start to use multiple wq_ctx
I believe this would should up as something fairly non-trivial to debug.

I think it's better to make this dead simple and assert that wq_ctx is 0
and just return the one and only completion.

> +
> +	err = idr_alloc_u32(&scm->waitq.idr, wq, &wq_ctx_idr,
> +			    U32_MAX, GFP_ATOMIC);

PS. Thinking about it further, imagine the firmware people deciding to
be funny and allocating the wq_ctx in a cyclic fashion. The idr will
consume all your ram after a while...

Regards,
Bjorn

> +	if (err < 0)
> +		wq = ERR_PTR(err);
> +
> +out:
> +	spin_unlock_irqrestore(&scm->waitq.idr_lock, flags);
> +	return wq;
> +}

Re: [PATCH V6 2/2] firmware: qcom: scm: Add wait-queue handling logic

[Guru Das Srinagesh]

On Dec 08 2022 16:11, Bjorn Andersson wrote:
> On Thu, Dec 08, 2022 at 12:10:31PM +0530, Sibi Sankar wrote:

...

> > +
> > +	err = idr_alloc_u32(&scm->waitq.idr, wq, &wq_ctx_idr,
> > +			    U32_MAX, GFP_ATOMIC);
> 
> PS. Thinking about it further, imagine the firmware people deciding to
> be funny and allocating the wq_ctx in a cyclic fashion. The idr will
> consume all your ram after a while...

Even if wq_ctx is allocated cyclically, say, from 1 to N, only N idrs would
ever be allocated as subsequently there would only be lookups. Could you
elaborate on how we would run out of RAM?

Thank you.

Guru Das.