[v12] Misc SCM driver changes

[PATCH v12 7/9] firmware: qcom: scm: Fix __scm->dev assignement

Posted by Mukesh Ojha 1 year, 10 months ago

qcom_scm_is_available() gives wrong indication if __scm
is initialized but __scm->dev is not.

Fix this appropriately by making sure if __scm is
initialized and then it is associated with its
device.

Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
---
 drivers/firmware/qcom/qcom_scm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
index 6c252cddd44e..6f14254c0c10 100644
--- a/drivers/firmware/qcom/qcom_scm.c
+++ b/drivers/firmware/qcom/qcom_scm.c
@@ -1859,6 +1859,7 @@ static int qcom_scm_probe(struct platform_device *pdev)
 	if (!scm)
 		return -ENOMEM;
 
+	scm->dev = &pdev->dev;
 	ret = qcom_scm_find_dload_address(&pdev->dev, &scm->dload_mode_addr);
 	if (ret < 0)
 		return ret;
@@ -1895,7 +1896,6 @@ static int qcom_scm_probe(struct platform_device *pdev)
 		return ret;
 
 	__scm = scm;
-	__scm->dev = &pdev->dev;
 
 	init_completion(&__scm->waitq_comp);
 
-- 
2.43.0.254.ga26002b62827

Re: [PATCH v12 7/9] firmware: qcom: scm: Fix __scm->dev assignement

Posted by Bjorn Andersson 1 year, 9 months ago

On Tue, Feb 27, 2024 at 09:23:06PM +0530, Mukesh Ojha wrote:
> qcom_scm_is_available() gives wrong indication if __scm
> is initialized but __scm->dev is not.
> 
> Fix this appropriately by making sure if __scm is
> initialized and then it is associated with its
> device.
> 

This seems like a bug fix, and should as such have a Fixes: tag and
probably Cc: stable@vger.kernel.org

> Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
> ---
>  drivers/firmware/qcom/qcom_scm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
> index 6c252cddd44e..6f14254c0c10 100644
> --- a/drivers/firmware/qcom/qcom_scm.c
> +++ b/drivers/firmware/qcom/qcom_scm.c
> @@ -1859,6 +1859,7 @@ static int qcom_scm_probe(struct platform_device *pdev)
>  	if (!scm)
>  		return -ENOMEM;
>  
> +	scm->dev = &pdev->dev;
>  	ret = qcom_scm_find_dload_address(&pdev->dev, &scm->dload_mode_addr);
>  	if (ret < 0)
>  		return ret;
> @@ -1895,7 +1896,6 @@ static int qcom_scm_probe(struct platform_device *pdev)
>  		return ret;
>  
>  	__scm = scm;
> -	__scm->dev = &pdev->dev;

Is it sufficient to just move the line up, or do we need a barrier of
some sort here?

Regards,
Bjorn

>  
>  	init_completion(&__scm->waitq_comp);
>  
> -- 
> 2.43.0.254.ga26002b62827
>

Re: [PATCH v12 7/9] firmware: qcom: scm: Fix __scm->dev assignement

Posted by Mukesh Ojha 1 year, 9 months ago


On 3/3/2024 12:55 AM, Bjorn Andersson wrote:
> On Tue, Feb 27, 2024 at 09:23:06PM +0530, Mukesh Ojha wrote:
>> qcom_scm_is_available() gives wrong indication if __scm
>> is initialized but __scm->dev is not.
>>
>> Fix this appropriately by making sure if __scm is
>> initialized and then it is associated with its
>> device.
>>
> 
> This seems like a bug fix, and should as such have a Fixes: tag and
> probably Cc: stable@vger.kernel.org
> 
>> Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
>> ---
>>   drivers/firmware/qcom/qcom_scm.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
>> index 6c252cddd44e..6f14254c0c10 100644
>> --- a/drivers/firmware/qcom/qcom_scm.c
>> +++ b/drivers/firmware/qcom/qcom_scm.c
>> @@ -1859,6 +1859,7 @@ static int qcom_scm_probe(struct platform_device *pdev)
>>   	if (!scm)
>>   		return -ENOMEM;
>>   
>> +	scm->dev = &pdev->dev;
>>   	ret = qcom_scm_find_dload_address(&pdev->dev, &scm->dload_mode_addr);
>>   	if (ret < 0)
>>   		return ret;
>> @@ -1895,7 +1896,6 @@ static int qcom_scm_probe(struct platform_device *pdev)
>>   		return ret;
>>   
>>   	__scm = scm;
>> -	__scm->dev = &pdev->dev;
> 
> Is it sufficient to just move the line up, or do we need a barrier of
> some sort here?

Would be good to use, smp_mb() before the assignment
      __scm = scm
along with moving below line
__scm->dev = &pdev->dev

somewhere up.

-Mukesh

> 
> Regards,
> Bjorn
> 
>>   
>>   	init_completion(&__scm->waitq_comp);
>>   
>> -- 
>> 2.43.0.254.ga26002b62827
>>

Re: [PATCH v12 7/9] firmware: qcom: scm: Fix __scm->dev assignement

Posted by Pavan Kondeti 1 year, 9 months ago

On Mon, Mar 18, 2024 at 06:38:20PM +0530, Mukesh Ojha wrote:
> 
> 
> On 3/3/2024 12:55 AM, Bjorn Andersson wrote:
> > On Tue, Feb 27, 2024 at 09:23:06PM +0530, Mukesh Ojha wrote:
> > > qcom_scm_is_available() gives wrong indication if __scm
> > > is initialized but __scm->dev is not.
> > > 
> > > Fix this appropriately by making sure if __scm is
> > > initialized and then it is associated with its
> > > device.
> > > 
> > 
> > This seems like a bug fix, and should as such have a Fixes: tag and
> > probably Cc: stable@vger.kernel.org
> > 
> > > Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
> > > ---
> > >   drivers/firmware/qcom/qcom_scm.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
> > > index 6c252cddd44e..6f14254c0c10 100644
> > > --- a/drivers/firmware/qcom/qcom_scm.c
> > > +++ b/drivers/firmware/qcom/qcom_scm.c
> > > @@ -1859,6 +1859,7 @@ static int qcom_scm_probe(struct platform_device *pdev)
> > >   	if (!scm)
> > >   		return -ENOMEM;
> > > +	scm->dev = &pdev->dev;
> > >   	ret = qcom_scm_find_dload_address(&pdev->dev, &scm->dload_mode_addr);
> > >   	if (ret < 0)
> > >   		return ret;
> > > @@ -1895,7 +1896,6 @@ static int qcom_scm_probe(struct platform_device *pdev)
> > >   		return ret;
> > >   	__scm = scm;
> > > -	__scm->dev = &pdev->dev;
> > 
> > Is it sufficient to just move the line up, or do we need a barrier of
> > some sort here?
> 
> Would be good to use, smp_mb() before the assignment
>      __scm = scm
> along with moving below line
> __scm->dev = &pdev->dev
> 

Full memory barrier is not needed here. store variant is sufficient.
WRITE_ONCE() + smp_store_release() will fit here no?

Thanks,
Pavan

Re: [PATCH v12 7/9] firmware: qcom: scm: Fix __scm->dev assignement

Posted by Mukesh Ojha 1 year, 9 months ago


On 3/19/2024 6:47 AM, Pavan Kondeti wrote:
> On Mon, Mar 18, 2024 at 06:38:20PM +0530, Mukesh Ojha wrote:
>>
>>
>> On 3/3/2024 12:55 AM, Bjorn Andersson wrote:
>>> On Tue, Feb 27, 2024 at 09:23:06PM +0530, Mukesh Ojha wrote:
>>>> qcom_scm_is_available() gives wrong indication if __scm
>>>> is initialized but __scm->dev is not.
>>>>
>>>> Fix this appropriately by making sure if __scm is
>>>> initialized and then it is associated with its
>>>> device.
>>>>
>>>
>>> This seems like a bug fix, and should as such have a Fixes: tag and
>>> probably Cc: stable@vger.kernel.org
>>>
>>>> Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
>>>> ---
>>>>    drivers/firmware/qcom/qcom_scm.c | 2 +-
>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
>>>> index 6c252cddd44e..6f14254c0c10 100644
>>>> --- a/drivers/firmware/qcom/qcom_scm.c
>>>> +++ b/drivers/firmware/qcom/qcom_scm.c
>>>> @@ -1859,6 +1859,7 @@ static int qcom_scm_probe(struct platform_device *pdev)
>>>>    	if (!scm)
>>>>    		return -ENOMEM;
>>>> +	scm->dev = &pdev->dev;
>>>>    	ret = qcom_scm_find_dload_address(&pdev->dev, &scm->dload_mode_addr);
>>>>    	if (ret < 0)
>>>>    		return ret;
>>>> @@ -1895,7 +1896,6 @@ static int qcom_scm_probe(struct platform_device *pdev)
>>>>    		return ret;
>>>>    	__scm = scm;
>>>> -	__scm->dev = &pdev->dev;
>>>
>>> Is it sufficient to just move the line up, or do we need a barrier of
>>> some sort here?
>>
>> Would be good to use, smp_mb() before the assignment
>>       __scm = scm
>> along with moving below line
>> __scm->dev = &pdev->dev
>>
> 
> Full memory barrier is not needed here. store variant is sufficient.
> WRITE_ONCE() + smp_store_release() will fit here no?

Thanks for the comment, i again have a look at it and agree we don't
need a full barrier here.

And we can do either of the below two ways.

-Mukesh


// 1st way

diff --git a/drivers/firmware/qcom/qcom_scm.c 
b/drivers/firmware/qcom/qcom_scm.c
index 49ddbcab0680..b638fb407fc6 100644
--- a/drivers/firmware/qcom/qcom_scm.c
+++ b/drivers/firmware/qcom/qcom_scm.c
@@ -1741,7 +1741,12 @@ static int qcom_scm_qseecom_init(struct qcom_scm 
*scm)
   */
  bool qcom_scm_is_available(void)
  {
-       return !!__scm;
+       bool avail;
   */
  bool qcom_scm_is_available(void)
  {
-       return !!__scm;
+       bool avail;
+
+       avail = !!READ_ONCE(__scm);
+       smp_rmb();
+
+       return avail;
  }
  EXPORT_SYMBOL_GPL(qcom_scm_is_available);

@@ -1822,10 +1827,12 @@ static int qcom_scm_probe(struct platform_device 
*pdev)
         if (!scm)
                 return -ENOMEM;

+       scm->dev = &pdev->dev;
         ret = qcom_scm_find_dload_address(&pdev->dev, 
&scm->dload_mode_addr);
         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);
@@ -1857,10 +1864,8 @@ static int qcom_scm_probe(struct platform_device 
*pdev)
         if (ret)
                 return ret;

-       __scm = scm;
-       __scm->dev = &pdev->dev;
-
-       init_completion(&__scm->waitq_comp);
+       smp_wmb();
+       WRITE_ONCE(__scm, scm);


// 2nd way

diff --git a/drivers/firmware/qcom/qcom_scm.c 
b/drivers/firmware/qcom/qcom_scm.c
index 49ddbcab0680..911699123f9f 100644
--- a/drivers/firmware/qcom/qcom_scm.c
+++ b/drivers/firmware/qcom/qcom_scm.c
@@ -1741,7 +1741,7 @@ static int qcom_scm_qseecom_init(struct qcom_scm *scm)
   */
  bool qcom_scm_is_available(void)
  {
-	return !!__scm;
+	return !!smp_load_acquire(&__scm);
  }
  EXPORT_SYMBOL_GPL(qcom_scm_is_available);

@@ -1822,10 +1822,12 @@ static int qcom_scm_probe(struct platform_device 
*pdev)
  	if (!scm)
  		return -ENOMEM;

+	scm->dev = &pdev->dev;
  	ret = qcom_scm_find_dload_address(&pdev->dev, &scm->dload_mode_addr);
  	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);
@@ -1857,10 +1859,8 @@ static int qcom_scm_probe(struct platform_device 
*pdev)
  	if (ret)
  		return ret;

-	__scm = scm;
-	__scm->dev = &pdev->dev;
-
-	init_completion(&__scm->waitq_comp);
+	/* Let all above stores available after this. */
+	smp_store_release(&__scm, scm);

  	irq = platform_get_irq_optional(pdev, 0);
  	if (irq < 0) {
-- 
2.7.4



> 
> Thanks,
> Pavan

Re: [PATCH v12 7/9] firmware: qcom: scm: Fix __scm->dev assignement

Posted by Pavan Kondeti 1 year, 9 months ago

On Tue, Mar 19, 2024 at 03:38:57PM +0530, Mukesh Ojha wrote:
> 
> 
> On 3/19/2024 6:47 AM, Pavan Kondeti wrote:
> > On Mon, Mar 18, 2024 at 06:38:20PM +0530, Mukesh Ojha wrote:
> > > 
> > > 
> > > On 3/3/2024 12:55 AM, Bjorn Andersson wrote:
> > > > On Tue, Feb 27, 2024 at 09:23:06PM +0530, Mukesh Ojha wrote:
> > > > > qcom_scm_is_available() gives wrong indication if __scm
> > > > > is initialized but __scm->dev is not.
> > > > > 
> > > > > Fix this appropriately by making sure if __scm is
> > > > > initialized and then it is associated with its
> > > > > device.
> > > > > 
> > > > 
> > > > This seems like a bug fix, and should as such have a Fixes: tag and
> > > > probably Cc: stable@vger.kernel.org
> > > > 
> > > > > Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
> > > > > ---
> > > > >    drivers/firmware/qcom/qcom_scm.c | 2 +-
> > > > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > 
> > > > > diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
> > > > > index 6c252cddd44e..6f14254c0c10 100644
> > > > > --- a/drivers/firmware/qcom/qcom_scm.c
> > > > > +++ b/drivers/firmware/qcom/qcom_scm.c
> > > > > @@ -1859,6 +1859,7 @@ static int qcom_scm_probe(struct platform_device *pdev)
> > > > >    	if (!scm)
> > > > >    		return -ENOMEM;
> > > > > +	scm->dev = &pdev->dev;
> > > > >    	ret = qcom_scm_find_dload_address(&pdev->dev, &scm->dload_mode_addr);
> > > > >    	if (ret < 0)
> > > > >    		return ret;
> > > > > @@ -1895,7 +1896,6 @@ static int qcom_scm_probe(struct platform_device *pdev)
> > > > >    		return ret;
> > > > >    	__scm = scm;
> > > > > -	__scm->dev = &pdev->dev;
> > > > 
> > > > Is it sufficient to just move the line up, or do we need a barrier of
> > > > some sort here?
> > > 
> > > Would be good to use, smp_mb() before the assignment
> > >       __scm = scm
> > > along with moving below line
> > > __scm->dev = &pdev->dev
> > > 
> > 
> > Full memory barrier is not needed here. store variant is sufficient.
> > WRITE_ONCE() + smp_store_release() will fit here no?
> 
> Thanks for the comment, i again have a look at it and agree we don't
> need a full barrier here.
> 
> And we can do either of the below two ways.
> 
> -Mukesh
> 
> 
> // 1st way
> 
> diff --git a/drivers/firmware/qcom/qcom_scm.c
> b/drivers/firmware/qcom/qcom_scm.c
> index 49ddbcab0680..b638fb407fc6 100644
> --- a/drivers/firmware/qcom/qcom_scm.c
> +++ b/drivers/firmware/qcom/qcom_scm.c
> @@ -1741,7 +1741,12 @@ static int qcom_scm_qseecom_init(struct qcom_scm
> *scm)
>   */
>  bool qcom_scm_is_available(void)
>  {
> -       return !!__scm;
> +       bool avail;
>   */
>  bool qcom_scm_is_available(void)
>  {
> -       return !!__scm;
> +       bool avail;
> +
> +       avail = !!READ_ONCE(__scm);
> +       smp_rmb();
> +
> +       return avail;
>  }
>  EXPORT_SYMBOL_GPL(qcom_scm_is_available);
> 

Your original problem statement: qcom_scm_is_available() gives wrong indication 
if __scm is initialized but __scm->dev is not.

This does not require read side barrier as there is an address
dependency. If the writer does it *correctly*, the reader would always
observe __scm->dev != NULL when __scm != NULL without any barrier.

Thanks,
Pavan

Re: [PATCH v12 7/9] firmware: qcom: scm: Fix __scm->dev assignement

Posted by Mukesh Ojha 1 year, 9 months ago


On 3/19/2024 3:52 PM, Pavan Kondeti wrote:
> On Tue, Mar 19, 2024 at 03:38:57PM +0530, Mukesh Ojha wrote:
>>
>>
>> On 3/19/2024 6:47 AM, Pavan Kondeti wrote:
>>> On Mon, Mar 18, 2024 at 06:38:20PM +0530, Mukesh Ojha wrote:
>>>>
>>>>
>>>> On 3/3/2024 12:55 AM, Bjorn Andersson wrote:
>>>>> On Tue, Feb 27, 2024 at 09:23:06PM +0530, Mukesh Ojha wrote:
>>>>>> qcom_scm_is_available() gives wrong indication if __scm
>>>>>> is initialized but __scm->dev is not.
>>>>>>
>>>>>> Fix this appropriately by making sure if __scm is
>>>>>> initialized and then it is associated with its
>>>>>> device.
>>>>>>
>>>>>
>>>>> This seems like a bug fix, and should as such have a Fixes: tag and
>>>>> probably Cc: stable@vger.kernel.org
>>>>>
>>>>>> Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
>>>>>> ---
>>>>>>     drivers/firmware/qcom/qcom_scm.c | 2 +-
>>>>>>     1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
>>>>>> index 6c252cddd44e..6f14254c0c10 100644
>>>>>> --- a/drivers/firmware/qcom/qcom_scm.c
>>>>>> +++ b/drivers/firmware/qcom/qcom_scm.c
>>>>>> @@ -1859,6 +1859,7 @@ static int qcom_scm_probe(struct platform_device *pdev)
>>>>>>     	if (!scm)
>>>>>>     		return -ENOMEM;
>>>>>> +	scm->dev = &pdev->dev;
>>>>>>     	ret = qcom_scm_find_dload_address(&pdev->dev, &scm->dload_mode_addr);
>>>>>>     	if (ret < 0)
>>>>>>     		return ret;
>>>>>> @@ -1895,7 +1896,6 @@ static int qcom_scm_probe(struct platform_device *pdev)
>>>>>>     		return ret;
>>>>>>     	__scm = scm;
>>>>>> -	__scm->dev = &pdev->dev;
>>>>>
>>>>> Is it sufficient to just move the line up, or do we need a barrier of
>>>>> some sort here?
>>>>
>>>> Would be good to use, smp_mb() before the assignment
>>>>        __scm = scm
>>>> along with moving below line
>>>> __scm->dev = &pdev->dev
>>>>
>>>
>>> Full memory barrier is not needed here. store variant is sufficient.
>>> WRITE_ONCE() + smp_store_release() will fit here no?
>>
>> Thanks for the comment, i again have a look at it and agree we don't
>> need a full barrier here.
>>
>> And we can do either of the below two ways.
>>
>> -Mukesh
>>
>>
>> // 1st way
>>
>> diff --git a/drivers/firmware/qcom/qcom_scm.c
>> b/drivers/firmware/qcom/qcom_scm.c
>> index 49ddbcab0680..b638fb407fc6 100644
>> --- a/drivers/firmware/qcom/qcom_scm.c
>> +++ b/drivers/firmware/qcom/qcom_scm.c
>> @@ -1741,7 +1741,12 @@ static int qcom_scm_qseecom_init(struct qcom_scm
>> *scm)
>>    */
>>   bool qcom_scm_is_available(void)
>>   {
>> -       return !!__scm;
>> +       bool avail;
>>    */
>>   bool qcom_scm_is_available(void)
>>   {
>> -       return !!__scm;
>> +       bool avail;
>> +
>> +       avail = !!READ_ONCE(__scm);
>> +       smp_rmb();
>> +
>> +       return avail;
>>   }
>>   EXPORT_SYMBOL_GPL(qcom_scm_is_available);
>>
> 
> Your original problem statement: qcom_scm_is_available() gives wrong indication
> if __scm is initialized but __scm->dev is not.
> 
> This does not require read side barrier as there is an address
> dependency. If the writer does it *correctly*, the reader would always
> observe __scm->dev != NULL when __scm != NULL without any barrier.

It looks like write barrier pairs with an address-dependency barrier, a
control dependency, an acquire barrier, a release barrier, a read 
barrier, or a general barrier.

So, smp_rmb() is redundant here.

Also, for correction, we may not need smp_load_acquire() in the 1st way
and just using READ_ONCE() is enough.

-Mukesh
> 
> Thanks,
> Pavan