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

[Unnathi Chalicheemala]

On 2/28/2024 3:20 PM, Chris Lew wrote:
> 
> 
> 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@xxxxxxxxxxx>
>> ---
>>  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.
> 
Apologies for the late reply Chris.
Yes, will move this check out side the do {} while() loop.

>> +			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.
> 

Thanks for pointing this out. Yes, this function is called every time a
qcom_smc_call() is made. But xarray documentation says that xa_store() uses
an internal xa_lock to synchronize accesses - I will look more into this.

To prevent rewriting entries at same wq_ctx, I think xa_store can be replaced
with xa_insert() - it'll prevent rewrite on existing entry.

>> +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?
> 

I'll check and remove if possible.
Thanks a lot for the review Chris!

> 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))
>>