Re: [PATCH V7 2/2] firmware: qcom: scm: Add wait-queue handling logic

[Srinivas Kandagatla <srinivas.kandagatla@linaro.org>]

Hi Sibi,

Few minor comments below,

On 10/01/2023 06:37, 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.
> 
...

>   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
...
> +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;

why are we checking dev pointer in the middle of the call?
A comment here would really help readers.

> +
> +			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;
> +}
> +
...
> 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>

include <linux/completion.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)
> +{
> +	/* assert wq_ctx is zero */ > +	if (wq_ctx != 0) {

Is this correct? looks like zero is the only valid one.

I thought wq_ctx was a unique number (UID).

> +		dev_err(scm->dev, "No waitqueue found for wq_ctx %d\n", wq_ctx);
> +		return ERR_PTR(-EINVAL);
> +	}
> +
> +	return &scm->waitq_comp;
> +}
> +
> +int qcom_scm_lookup_completion(u32 wq_ctx)
> +{
> +	struct completion *wq = NULL;
> +
> +	wq = qcom_scm_lookup_wq(__scm, wq_ctx);
> +	if (IS_ERR(wq))
> +		return PTR_ERR(wq);
> +
> +	wait_for_completion(wq);

We can potentially block here forever without a timeout.

As you are reusing completion, I have not seen any reinitialization of 
completion, this could potentially return above line without waiting at all.

> +
> +	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_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();
>   
>   	/*

--srini