Re: [PATCH 2/3] firmware: qcom-scm: Support multiple waitq contexts

[Chris Lew <quic_clew@quicinc.com>]

On 2/28/2024 10:50 AM, Unnathi Chalicheemala wrote:
> Currently, only a single waitqueue context is supported, with waitqueue
> id zero. SM8650 firmware now supports multiple waitqueue contexts, so
> add support to dynamically create and support as many unique waitqueue
> contexts as firmware returns to the driver.
> Unique waitqueue contexts are supported using xarray to create a
> hash table for associating a unique wq_ctx with a struct completion
> variable for easy lookup.
> The waitqueue ids can be >=0 as now we have more than one waitqueue
> context.
> 
> Signed-off-by: Unnathi Chalicheemala <quic_uchalich@quicinc.com>
> ---
>  drivers/firmware/qcom/qcom_scm-smc.c |  7 +++-
>  drivers/firmware/qcom/qcom_scm.c     | 77 ++++++++++++++++++++++++++----------
>  drivers/firmware/qcom/qcom_scm.h     |  3 +-
>  3 files changed, 64 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/firmware/qcom/qcom_scm-smc.c b/drivers/firmware/qcom/qcom_scm-smc.c
> index 16cf88acfa8e..80083e3615b1 100644
> --- a/drivers/firmware/qcom/qcom_scm-smc.c
> +++ b/drivers/firmware/qcom/qcom_scm-smc.c
> @@ -103,7 +103,12 @@ static int __scm_smc_do_quirk_handle_waitq(struct device *dev, struct arm_smccc_
>  			wq_ctx = res->a1;
>  			smc_call_ctx = res->a2;
>  
> -			ret = qcom_scm_wait_for_wq_completion(wq_ctx);
> +			if (!dev) {
> +				/* Protect the dev_get_drvdata() call that follows */
> +				return -EPROBE_DEFER;
> +			}
> +

Do we need to do this !dev check within the do/while loop? Seems like it
could be done once at the start.

> +			ret = qcom_scm_wait_for_wq_completion(dev_get_drvdata(dev), wq_ctx);
>  			if (ret)
>  				return ret;
>  
> diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
> index c1be8270ead1..4606c49ef155 100644
> --- a/drivers/firmware/qcom/qcom_scm.c
> +++ b/drivers/firmware/qcom/qcom_scm.c
> @@ -21,6 +21,7 @@
>  #include <linux/platform_device.h>
>  #include <linux/reset-controller.h>
>  #include <linux/types.h>
> +#include <linux/xarray.h>
>  
>  #include "qcom_scm.h"
>  
> @@ -33,7 +34,7 @@ struct qcom_scm {
>  	struct clk *iface_clk;
>  	struct clk *bus_clk;
>  	struct icc_path *path;
> -	struct completion waitq_comp;
> +	struct xarray waitq;
>  	struct reset_controller_dev reset;
>  
>  	/* control access to the interconnect path */
> @@ -1742,42 +1743,74 @@ bool qcom_scm_is_available(void)
>  }
>  EXPORT_SYMBOL_GPL(qcom_scm_is_available);
>  
> -static int qcom_scm_assert_valid_wq_ctx(u32 wq_ctx)
> +static struct completion *qcom_scm_get_completion(struct qcom_scm *scm, 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.
> +	struct completion *wq;
> +	struct completion *old;
> +	int err;
> +
> +	wq = xa_load(&scm->waitq, wq_ctx);
> +	if (wq) {
> +		/*
> +		 * Valid struct completion *wq found corresponding to
> +		 * given wq_ctx. We're done here.
> +		 */
> +		goto out;
> +	}
> +
> +	/*
> +	 * If a struct completion *wq does not exist for wq_ctx, create it. FW
> +	 * only uses a finite number of wq_ctx values, so we will be reaching
> +	 * here only a few times right at the beginning of the device's uptime
> +	 * and then early-exit from idr_find() above subsequently.
>  	 */
> -	if (wq_ctx != 0) {
> -		dev_err(__scm->dev, "Firmware unexpectedly passed non-zero wq_ctx\n");
> -		return -EINVAL;
> +	wq = kzalloc(sizeof(*wq), GFP_ATOMIC);
> +	if (!wq) {
> +		wq = ERR_PTR(-ENOMEM);
> +		goto out;
>  	}
>  
> -	return 0;
> +	init_completion(wq);
> +
> +	old = xa_store(&scm->waitq, wq_ctx, wq, GFP_ATOMIC);
> +	err = xa_err(old);
> +	if (err) {
> +		kfree(wq);
> +		wq = ERR_PTR(err);
> +	}
> +

Any chance for this function to be called concurrently before there is a
valid wq stored in the xarray? If that were to happen we could have two
valid xa_stores happen on the same wq_ctx. One of the entries would be
returned as old and might be leaked depending on timing.

> +out:
> +	return wq;
>  }
>  
> -int qcom_scm_wait_for_wq_completion(u32 wq_ctx)
> +int qcom_scm_wait_for_wq_completion(struct qcom_scm *scm, u32 wq_ctx)
>  {
> -	int ret;
> +	struct completion *wq;
>  
> -	ret = qcom_scm_assert_valid_wq_ctx(wq_ctx);
> -	if (ret)
> -		return ret;
> +	wq = qcom_scm_get_completion(scm, wq_ctx);
> +	if (IS_ERR(wq)) {
> +		pr_err("Unable to wait on invalid waitqueue for wq_ctx %d: %ld\n",
> +						wq_ctx, PTR_ERR(wq));
> +		return PTR_ERR(wq);
> +	}
>  
> -	wait_for_completion(&__scm->waitq_comp);
> +	wait_for_completion(wq);
>  
>  	return 0;
>  }
>  
>  static int qcom_scm_waitq_wakeup(struct qcom_scm *scm, unsigned int wq_ctx)
>  {
> -	int ret;
> +	struct completion *wq;
>  
> -	ret = qcom_scm_assert_valid_wq_ctx(wq_ctx);
> -	if (ret)
> -		return ret;
> +	wq = qcom_scm_get_completion(scm, wq_ctx);
> +	if (IS_ERR(wq)) {
> +		pr_err("Unable to wake up invalid waitqueue for wq_ctx %d: %ld\n",
> +						wq_ctx, PTR_ERR(wq));
> +		return PTR_ERR(wq);
> +	}
>  
> -	complete(&__scm->waitq_comp);
> +	complete(wq);
>  
>  	return 0;
>  }
> @@ -1854,7 +1887,9 @@ static int qcom_scm_probe(struct platform_device *pdev)
>  	if (ret)
>  		return ret;
>  
> -	init_completion(&scm->waitq_comp);
> +	platform_set_drvdata(pdev, scm);
> +
> +	xa_init(&scm->waitq);
>  
>  	__scm = scm;
>  	__scm->dev = &pdev->dev;
> diff --git a/drivers/firmware/qcom/qcom_scm.h b/drivers/firmware/qcom/qcom_scm.h
> index 4532907e8489..d54df5a2b690 100644
> --- a/drivers/firmware/qcom/qcom_scm.h
> +++ b/drivers/firmware/qcom/qcom_scm.h
> @@ -62,7 +62,8 @@ struct qcom_scm_res {
>  	u64 result[MAX_QCOM_SCM_RETS];
>  };
>  
> -int qcom_scm_wait_for_wq_completion(u32 wq_ctx);
> +struct qcom_scm;
> +int qcom_scm_wait_for_wq_completion(struct qcom_scm *scm, u32 wq_ctx);

Is there a benefit to having qcom_scm passed in? I see we're adding scm
as drvdata in this patch, but we still have a single global __scm
pointer in qcom_scm.c. Are there going to be multiple instances of the
qcom_scm device?

Thanks,
Chris

>  int scm_get_wq_ctx(u32 *wq_ctx, u32 *flags, u32 *more_pending);
>  
>  #define SCM_SMC_FNID(s, c)	((((s) & 0xFF) << 8) | ((c) & 0xFF))
>