[Linaro-mm-sig] [PATCH 1/9] dma-buf: consolidate dma_fence subclass checking

[Christian König]

Am 21.01.22 um 08:41 schrieb Thomas Hellström (Intel):
>
> On 1/20/22 14:27, Christian König wrote:
>> Consolidate the wrapper functions to check for dma_fence
>> subclasses in the dma_fence header.
>>
>> This makes it easier to document and also check the different
>> requirements for fence containers in the subclasses.
>>
>> Signed-off-by: Christian König <christian.koenig at amd.com>
>> ---
>>   include/linux/dma-fence-array.h | 15 +------------
>>   include/linux/dma-fence-chain.h |  3 +--
>>   include/linux/dma-fence.h       | 38 +++++++++++++++++++++++++++++++++
>>   3 files changed, 40 insertions(+), 16 deletions(-)
>>
>> diff --git a/include/linux/dma-fence-array.h 
>> b/include/linux/dma-fence-array.h
>> index 303dd712220f..fec374f69e12 100644
>> --- a/include/linux/dma-fence-array.h
>> +++ b/include/linux/dma-fence-array.h
>> @@ -45,19 +45,6 @@ struct dma_fence_array {
>>       struct irq_work work;
>>   };
>>   -extern const struct dma_fence_ops dma_fence_array_ops;
>> -
>> -/**
>> - * dma_fence_is_array - check if a fence is from the array subsclass
>> - * @fence: fence to test
>> - *
>> - * Return true if it is a dma_fence_array and false otherwise.
>> - */
>> -static inline bool dma_fence_is_array(struct dma_fence *fence)
>> -{
>> -    return fence->ops == &dma_fence_array_ops;
>> -}
>> -
>>   /**
>>    * to_dma_fence_array - cast a fence to a dma_fence_array
>>    * @fence: fence to cast to a dma_fence_array
>> @@ -68,7 +55,7 @@ static inline bool dma_fence_is_array(struct 
>> dma_fence *fence)
>>   static inline struct dma_fence_array *
>>   to_dma_fence_array(struct dma_fence *fence)
>>   {
>> -    if (fence->ops != &dma_fence_array_ops)
>> +    if (!fence || !dma_fence_is_array(fence))
>>           return NULL;
>>         return container_of(fence, struct dma_fence_array, base);
>> diff --git a/include/linux/dma-fence-chain.h 
>> b/include/linux/dma-fence-chain.h
>> index 54fe3443fd2c..ee906b659694 100644
>> --- a/include/linux/dma-fence-chain.h
>> +++ b/include/linux/dma-fence-chain.h
>> @@ -49,7 +49,6 @@ struct dma_fence_chain {
>>       spinlock_t lock;
>>   };
>>   -extern const struct dma_fence_ops dma_fence_chain_ops;
>>     /**
>>    * to_dma_fence_chain - cast a fence to a dma_fence_chain
>> @@ -61,7 +60,7 @@ extern const struct dma_fence_ops dma_fence_chain_ops;
>>   static inline struct dma_fence_chain *
>>   to_dma_fence_chain(struct dma_fence *fence)
>>   {
>> -    if (!fence || fence->ops != &dma_fence_chain_ops)
>> +    if (!fence || !dma_fence_is_chain(fence))
>>           return NULL;
>>         return container_of(fence, struct dma_fence_chain, base);
>> diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
>> index 1ea691753bd3..775cdc0b4f24 100644
>> --- a/include/linux/dma-fence.h
>> +++ b/include/linux/dma-fence.h
>> @@ -587,4 +587,42 @@ struct dma_fence *dma_fence_get_stub(void);
>>   struct dma_fence *dma_fence_allocate_private_stub(void);
>>   u64 dma_fence_context_alloc(unsigned num);
>>   +extern const struct dma_fence_ops dma_fence_array_ops;
>> +extern const struct dma_fence_ops dma_fence_chain_ops;
>> +
>> +/**
>> + * dma_fence_is_array - check if a fence is from the array subclass
>> + * @fence: the fence to test
>> + *
>> + * Return true if it is a dma_fence_array and false otherwise.
>> + */
>> +static inline bool dma_fence_is_array(struct dma_fence *fence)
>> +{
>> +    return fence->ops == &dma_fence_array_ops;
>> +}
>> +
>> +/**
>> + * dma_fence_is_chain - check if a fence is from the chain subclass
>> + * @fence: the fence to test
>> + *
>> + * Return true if it is a dma_fence_chain and false otherwise.
>> + */
>> +static inline bool dma_fence_is_chain(struct dma_fence *fence)
>> +{
>> +    return fence->ops == &dma_fence_chain_ops;
>> +}
>> +
>> +/**
>> + * dma_fence_is_container - check if a fence is a container for 
>> other fences
>> + * @fence: the fence to test
>> + *
>> + * Return true if this fence is a container for other fences, false 
>> otherwise.
>> + * This is important since we can't build up large fence structure 
>> or otherwise
>> + * we run into recursion during operation on those fences.
>> + */
>> +static inline bool dma_fence_is_container(struct dma_fence *fence)
>> +{
>> +    return dma_fence_is_array(fence) || dma_fence_is_chain(fence);
>> +}
>
> What's the strategy here moving forward if we add more dma_resv 
> containers, or if a driver adds a container that similarly has risc of 
> recursion? Should we perhaps add an ops bool for this, or require that 
> all dma_resv containers that has this limitation be part of the 
> dma-buf subsystem rather than driver-specific?

Good question.

I think that all containers which also implement the dma_fence interface 
should be part of the DMA-buf subsystem and not driver specific. Drivers 
just tend to reinvent something incorrectly.

Where/How should we document that?

Regards,
Christian.

>
> Thanks,
> /Thomas
>
>
>> +
>>   #endif /* __LINUX_DMA_FENCE_H */