Re: [PATCH v2 2/2] firmware: qcom_scm: Support multiple waitq contexts

[Unnathi Chalicheemala <quic_uchalich@quicinc.com>]

On 9/4/2024 2:54 PM, Bjorn Andersson wrote:
> On Thu, Aug 29, 2024 at 03:15:55PM GMT, Unnathi Chalicheemala wrote:
>> Currently, only a single waitqueue context exists, with waitqueue id zero.
>> Multi-waitqueue mechanism is added in firmware to support the case when
>> multiple VMs make SMC calls or single VM making multiple calls on same CPU.
>>
>> When VMs make SMC call, firmware will allocate waitqueue context assuming
>> the SMC call to be a blocking call. SMC calls that cannot acquire resources
>> are returned to sleep in the calling VM. When resource is available, VM
>> will be notified to wake sleeping thread and resume SMC call.
>> SM8650 firmware can allocate two such waitq contexts so create these two
>> waitqueue contexts.
>>
>> Unique waitqueue contexts are supported by a dynamically sized array where
>> each unique wq_ctx is associated with a struct completion variable for easy
>> lookup. To get the number of waitqueue contexts directly from firmware,
>> qcom_scm_query_waitq_cnt() is introduced. On older targets which support
>> only a single waitqueue, wq_cnt is set to 1 as SCM call for
>> query_waitq_cnt() is not implemented for single waitqueue case.
>>
>> Signed-off-by: Unnathi Chalicheemala <quic_uchalich@quicinc.com>
>> ---
>>  drivers/firmware/qcom/qcom_scm.c | 82 +++++++++++++++++++++++---------
>>  1 file changed, 60 insertions(+), 22 deletions(-)
>>
>> diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
>> index ed51fbb1c065..b2c5505de681 100644
>> --- a/drivers/firmware/qcom/qcom_scm.c
>> +++ b/drivers/firmware/qcom/qcom_scm.c
>> @@ -44,12 +44,13 @@ static bool download_mode = IS_ENABLED(CONFIG_QCOM_SCM_DOWNLOAD_MODE_DEFAULT);
>>  module_param(download_mode, bool, 0);
>>  
>>  struct qcom_scm {
>> +	int wq_cnt;
> 
> Does it make sense for this to be negative? Please make it unsigned.
> 
> Also, might not be the most significant member of this struct, so
> perhaps you can move it further down?
> 
Ack.
>>  	struct device *dev;
>>  	struct clk *core_clk;
>>  	struct clk *iface_clk;
>>  	struct clk *bus_clk;
>>  	struct icc_path *path;
>> -	struct completion waitq_comp;
>> +	struct completion *waitq;
>>  	struct reset_controller_dev reset;
>>  
>>  	/* control access to the interconnect path */
>> @@ -1850,6 +1851,31 @@ static int qcom_scm_fill_irq_fwspec_params(struct irq_fwspec *fwspec, u32 virq)
>>  	return 0;
>>  }
>>  
>> +static int qcom_scm_query_waitq_count(void)
>> +{
>> +	bool avail;
>> +	int count;
>> +	int ret;
>> +	struct qcom_scm_desc desc = {
>> +		.svc = QCOM_SCM_SVC_WAITQ,
>> +		.cmd = QCOM_SCM_WAITQ_GET_INFO,
>> +		.owner = ARM_SMCCC_OWNER_SIP
>> +	};
>> +	struct qcom_scm_res res;
>> +
>> +	avail = __qcom_scm_is_call_available(__scm->dev, QCOM_SCM_SVC_WAITQ, QCOM_SCM_WAITQ_GET_INFO);
>> +	if (!avail) {
>> +		count = 1;
>> +		return count;
> 
> count is a local variable, so just return count; and drop the {} please.
> 
> 
> Perhaps even drop the local boolean variable:
> 
> 	if (!__qcom_scm_is_call_available(__scm->dev, QCOM_SCM_SVC_WAITQ, QCOM_SCM_WAITQ_GET_INFO))
> 		return 1;
> 
Ack.
>> +	}
>> +
>> +	ret = qcom_scm_call_atomic(__scm->dev, &desc, &res);
>> +	if (ret)
> 
> (Keep this local variable, as that's in line with the style...)
> 
>> +		return ret;
>> +	count = res.result[0] & 0xff;
>> +	return count;
> 
> Again, return res.result[0] & 0xff; should be sufficient, no need for a
> local variable immediately followed by a return statement.
> 
Ack.
>> +}
>> +
>>  static int qcom_scm_get_waitq_irq(void)
>>  {
>>  	int ret;
>> @@ -1876,42 +1902,40 @@ static int qcom_scm_get_waitq_irq(void)
>>  	return ret;
>>  }
>>  
>> -static int qcom_scm_assert_valid_wq_ctx(u32 wq_ctx)
>> +static struct completion *qcom_scm_get_completion(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;
>> -	}
>> +	struct completion *wq;
>>  
>> -	return 0;
>> +	if (wq_ctx >= __scm->wq_cnt)
> 
> I'm guessing that we're not expecting to ever hit this, but if we do, we
> will fail a qcom_scm_call() or qcom_scm_call_atomic() call, giving
> someone down the road a bad week of debugging...
> 
> How about wrapping the conditional in a WARN_ON_ONCE()?
> 
Yes understood, ack.
>> +		return ERR_PTR(-EINVAL);
>> +
>> +	wq = &__scm->waitq[wq_ctx];
>> +
>> +	return wq;
>>  }
>>  
>>  int qcom_scm_wait_for_wq_completion(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(wq_ctx);
>> +	if (IS_ERR(wq))
>> +		return PTR_ERR(wq);
>>  
>> -	wait_for_completion(&__scm->waitq_comp);
>> +	wait_for_completion(wq);
>>  
>>  	return 0;
>>  }
>>  
>>  static int qcom_scm_waitq_wakeup(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(wq_ctx);
>> +	if (IS_ERR(wq))
>> +		return PTR_ERR(wq);
>>  
>> -	complete(&__scm->waitq_comp);
>> +	complete(wq);
>>  
>>  	return 0;
>>  }
>> @@ -1948,6 +1972,7 @@ static int qcom_scm_probe(struct platform_device *pdev)
>>  	struct qcom_tzmem_pool_config pool_config;
>>  	struct qcom_scm *scm;
>>  	int irq, ret;
>> +	int i;
>>  
>>  	scm = devm_kzalloc(&pdev->dev, sizeof(*scm), GFP_KERNEL);
>>  	if (!scm)
>> @@ -1958,7 +1983,6 @@ static int qcom_scm_probe(struct platform_device *pdev)
>>  	if (ret < 0)
>>  		return ret;
>>  
>> -	init_completion(&scm->waitq_comp);
>>  	mutex_init(&scm->scm_bw_lock);
>>  
>>  	scm->path = devm_of_icc_get(&pdev->dev, NULL);
>> @@ -1993,6 +2017,20 @@ static int qcom_scm_probe(struct platform_device *pdev)
>>  	/* Let all above stores be available after this */
>>  	smp_store_release(&__scm, scm);
> 
> Should have spotted this earlier... But if any code below this point
> takes an error path (i.e. we return non-0 from hereon) devres will free
> __scm and anyone calling the qcom_scm API will hit a use-after-free.
> 
> Add to that it doesn't seem like a good idea to have
> qcom_scm_is_available() return true until we have setup the wait queue
> count or setup tzmem at least.
> 
Would the other calls that go through error path below need to be before the smp_store_release?
Just wondering if that needs to be fixed in a separate patch..

And I think the waitq initialization before the smp_store_release should be okay.
>>  
>> +	platform_set_drvdata(pdev, scm);
> 
> I believe this is a leftover from previous versions of this patch?
> 
Yes, will remove this.
> Regards,
> Bjorn
> 
>> +	ret = qcom_scm_query_waitq_count();
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	scm->wq_cnt = ret;
>> +
>> +	scm->waitq = devm_kcalloc(&pdev->dev, scm->wq_cnt, sizeof(*scm->waitq), GFP_KERNEL);
>> +	if (!scm->waitq)
>> +		return -ENOMEM;
>> +
>> +	for (i = 0; i < scm->wq_cnt; i++)
>> +		init_completion(&scm->waitq[i]);
>> +
>>  	irq = qcom_scm_get_waitq_irq();
>>  	if (irq < 0) {
>>  		if (irq != -ENXIO)
>> -- 
>> 2.34.1
>>
>