RE: [PATCH] staging: android: ion: add buffer flag update ioctl

[Zengtao (B)]

>-----Original Message-----
>From: Laura Abbott [mailto:labbott@xxxxxxxxxx]
>Sent: Thursday, January 03, 2019 6:31 AM
>To: Zengtao (B) <prime.zeng@xxxxxxxxxxxxx>; sumit.semwal@xxxxxxxxxx
>Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>; Arve HjÃnnevÃg
><arve@xxxxxxxxxxx>; Todd Kjos <tkjos@xxxxxxxxxxx>; Martijn Coenen
><maco@xxxxxxxxxxx>; Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>;
>devel@xxxxxxxxxxxxxxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx;
>linaro-mm-sig@xxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
>Subject: Re: [PATCH] staging: android: ion: add buffer flag update ioctl
>
>On 12/23/18 6:47 PM, Zengtao (B) wrote:
>> Hi laura:
>>
>>> -----Original Message-----
>>> From: Laura Abbott [mailto:labbott@xxxxxxxxxx]
>>> Sent: Friday, December 21, 2018 4:50 AM
>>> To: Zengtao (B) <prime.zeng@xxxxxxxxxxxxx>;
>sumit.semwal@xxxxxxxxxx
>>> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>; Arve
>HjÃnnevÃg
>>> <arve@xxxxxxxxxxx>; Todd Kjos <tkjos@xxxxxxxxxxx>; Martijn
>Coenen
>>> <maco@xxxxxxxxxxx>; Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>;
>>> devel@xxxxxxxxxxxxxxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx;
>>> linaro-mm-sig@xxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
>>> Subject: Re: [PATCH] staging: android: ion: add buffer flag update
>>> ioctl
>>>
>>> On 12/19/18 5:39 PM, Zengtao (B) wrote:
>>>> Hi laura:
>>>>
>>>>> -----Original Message-----
>>>>> From: Laura Abbott [mailto:labbott@xxxxxxxxxx]
>>>>> Sent: Thursday, December 20, 2018 2:10 AM
>>>>> To: Zengtao (B) <prime.zeng@xxxxxxxxxxxxx>;
>>> sumit.semwal@xxxxxxxxxx
>>>>> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>; Arve
>>> HjÃnnevÃg
>>>>> <arve@xxxxxxxxxxx>; Todd Kjos <tkjos@xxxxxxxxxxx>; Martijn
>>> Coenen
>>>>> <maco@xxxxxxxxxxx>; Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>;
>>>>> devel@xxxxxxxxxxxxxxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx;
>>>>> linaro-mm-sig@xxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
>>>>> Subject: Re: [PATCH] staging: android: ion: add buffer flag update
>>>>> ioctl
>>>>>
>>>>> On 12/19/18 9:19 AM, Zeng Tao wrote:
>>>>>> In some usecases, the buffer cached attribute is not determined at
>>>>>> allocation time, it's determined just before the real cpu mapping.
>>>>>> And from the memory view of point, a buffer should not have the
>>>>> cached
>>>>>> attribute util is really mapped by the cpu. So in this patch, we
>>>>>> introduced the new ioctl command to target the requirement.
>>>>>>
>>>>>
>>>>> This is racy and error prone. Can you explain more what problem
>you
>>>>> are trying to solve?
>>>>
>>>> My use case is like this:
>>>> 1.  There are two process A and B, A takes case of ion buffer
>>>> allocation,
>>> and
>>>>    pass the buffer fd to B, then B maps and uses it.
>>>> 2.  Process B need to map the buffer with different cached attribute
>>>> for different use case, for example, if the buffer is used for pure
>>>> software algorithm, then we need to map it as cached, otherwise
>>>> non-cached, and B needs to deal with both cases.
>>>> And unfortunately the mmap syscall takes no cached flags and we
>>>> can't decide the cache attribute when we are doing the mmap, so I
>>>> introduce new the ioctl even though I think the solution is not as
>good.
>>>>
>>>>
>>>
>>> Thanks for the explanation, this was about the use case I expected.
>>> I'm pretty sure I had this exact problem once upon a time and we
>>> didn't come up with a solution. I'd still like to get rid of uncached
>>> buffers in general and just use cached buffers (see
>>> http://driverdev.linuxdriverproject.org/pipermail/driverdev-devel/201
>>> 8-N
>>> ovember/128842.html)
>>> What's your usecase for uncached buffers?
>>
>> Some buffers are only used by HW, in this case, we tend to use
>uncached buffers.
>> But sometimes the SW need to read few buffer contents for debug
>> purpose and no synchronization is needed.
>>
>
>If this is primarily for debug, that's not really a compelling reason to
>support uncached buffers. It's incredibly difficult to do uncached buffers
>correctly I'd rather spend effort on making the cached use cases work
>better.
>
No, not only for debug, I meant if the buffers are uncached, the SW will only mmap
them for debug or even don't need to mmap them.
So for the two kinds of buffers:
1.  uncached: only the HW need to access it, the SW don't need to mmap it or just for debug.
2.  cached: both the HW and the SW need to access it.
The ION is designed as a generalized memory manager, I think we should cover as many 
requirements as we can in the ION design, so I 'd rather that we keep the uncached support.
And I donât quite understand the difficulty you mentioned to support the uncached buffers, would
you explain a little more about it.

Thanks 
Zengtao 

>
>>>
>>>>>
>>>>>> Signed-off-by: Zeng Tao <prime.zeng@xxxxxxxxxxxxx>
>>>>>> ---
>>>>>>     drivers/staging/android/ion/ion-ioctl.c |  4 ++++
>>>>>>     drivers/staging/android/ion/ion.c       | 17
>>> +++++++++++++++++
>>>>>>     drivers/staging/android/ion/ion.h       |  1 +
>>>>>>     drivers/staging/android/uapi/ion.h      | 22
>>>>> ++++++++++++++++++++++
>>>>>>     4 files changed, 44 insertions(+)
>>>>>>
>>>>>> diff --git a/drivers/staging/android/ion/ion-ioctl.c
>>>>>> b/drivers/staging/android/ion/ion-ioctl.c
>>>>>> index a8d3cc4..60bb702 100644
>>>>>> --- a/drivers/staging/android/ion/ion-ioctl.c
>>>>>> +++ b/drivers/staging/android/ion/ion-ioctl.c
>>>>>> @@ -12,6 +12,7 @@
>>>>>>
>>>>>>     union ion_ioctl_arg {
>>>>>>     	struct ion_allocation_data allocation;
>>>>>> +	struct ion_buffer_flag_data update;
>>>>>>     	struct ion_heap_query query;
>>>>>>     };
>>>>>>
>>>>>> @@ -83,6 +84,9 @@ long ion_ioctl(struct file *filp, unsigned int
>>>>>> cmd, unsigned long arg)
>>>>>>
>>>>>>     		break;
>>>>>>     	}
>>>>>> +	case ION_IOC_BUFFER_UPDATE:
>>>>>> +		ret = ion_buffer_update(data.update.fd, data.update.flags);
>>>>>> +		break;
>>>>>>     	case ION_IOC_HEAP_QUERY:
>>>>>>     		ret = ion_query_heaps(&data.query);
>>>>>>     		break;
>>>>>> diff --git a/drivers/staging/android/ion/ion.c
>>>>>> b/drivers/staging/android/ion/ion.c
>>>>>> index 9907332..f1404dc 100644
>>>>>> --- a/drivers/staging/android/ion/ion.c
>>>>>> +++ b/drivers/staging/android/ion/ion.c
>>>>>> @@ -436,6 +436,23 @@ int ion_alloc(size_t len, unsigned int
>>>>> heap_id_mask, unsigned int flags)
>>>>>>     	return fd;
>>>>>>     }
>>>>>>
>>>>>> +int ion_buffer_update(unsigned int fd, unsigned int flags) {
>>>>>> +	struct dma_buf *dmabuf;
>>>>>> +	struct ion_buffer *buffer;
>>>>>> +
>>>>>> +	dmabuf = dma_buf_get(fd);
>>>>>> +
>>>>>> +	if (!dmabuf)
>>>>>> +		return -EINVAL;
>>>>>> +
>>>>>> +	buffer = dmabuf->priv;
>>>>>> +	buffer->flags = flags;
>>>>>> +	dma_buf_put(dmabuf);
>>>>>> +
>>>>>> +	return 0;
>>>>>> +}
>>>>>> +
>>>>>>     int ion_query_heaps(struct ion_heap_query *query)
>>>>>>     {
>>>>>>     	struct ion_device *dev = internal_dev; diff --git
>>>>>> a/drivers/staging/android/ion/ion.h
>>>>>> b/drivers/staging/android/ion/ion.h
>>>>>> index c006fc1..99bf9ab 100644
>>>>>> --- a/drivers/staging/android/ion/ion.h
>>>>>> +++ b/drivers/staging/android/ion/ion.h
>>>>>> @@ -199,6 +199,7 @@ int ion_heap_pages_zero(struct page
>*page,
>>>>> size_t size, pgprot_t pgprot);
>>>>>>     int ion_alloc(size_t len,
>>>>>>     	      unsigned int heap_id_mask,
>>>>>>     	      unsigned int flags);
>>>>>> +int ion_buffer_update(unsigned int fd, unsigned int flags);
>>>>>>
>>>>>>     /**
>>>>>>      * ion_heap_init_shrinker
>>>>>> diff --git a/drivers/staging/android/uapi/ion.h
>>>>>> b/drivers/staging/android/uapi/ion.h
>>>>>> index 5d70098..99753fc 100644
>>>>>> --- a/drivers/staging/android/uapi/ion.h
>>>>>> +++ b/drivers/staging/android/uapi/ion.h
>>>>>> @@ -74,6 +74,20 @@ struct ion_allocation_data {
>>>>>>     	__u32 unused;
>>>>>>     };
>>>>>>
>>>>>> +/**
>>>>>> + * struct ion_buffer_flag_data - metadata passed from userspace
>>>>>> +for update
>>>>>> + * buffer flags
>>>>>> + * @fd:			file descriptor of the buffer
>>>>>> + * @flags:		flags passed to the buffer
>>>>>> + *
>>>>>> + * Provided by userspace as an argument to the ioctl  */
>>>>>> +
>>>>>> +struct ion_buffer_flag_data {
>>>>>> +	__u32 fd;
>>>>>> +	__u32 flags;
>>>>>> +}
>>>>>> +
>>>>>>     #define MAX_HEAP_NAME			32
>>>>>>
>>>>>>     /**
>>>>>> @@ -116,6 +130,14 @@ struct ion_heap_query {
>>>>>>     				      struct ion_allocation_data)
>>>>>>
>>>>>>     /**
>>>>>> + * DOC: ION_IOC_BUFFER_UPDATE - update the specified ion
>buffer
>>>>> flags
>>>>>> + *
>>>>>> + * Takes an ion_buffer_flag_data structure and returns the result
>>>>>> +of the
>>>>>> + * buffer flag update operation.
>>>>>> + */
>>>>>> +#define ION_IOC_BUFFER_UPDATE	_IOWR(ION_IOC_MAGIC, 1, \
>>>>>> +				      struct ion_buffer_flag_data)
>>>>>> +/**
>>>>>>      * DOC: ION_IOC_HEAP_QUERY - information about available
>>> heaps
>>>>>>      *
>>>>>>      * Takes an ion_heap_query structure and populates
>information
>>>>> about
>>>>>>
>>>>
>>