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

["Zengtao (B)" <prime.zeng@hisilicon.com>]

Hi laura:

>-----Original Message-----
>From: Laura Abbott [mailto:labbott@redhat.com]
>Sent: Friday, December 21, 2018 4:50 AM
>To: Zengtao (B) <prime.zeng@hisilicon.com>; sumit.semwal@linaro.org
>Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>; Arve Hjønnevåg
><arve@android.com>; Todd Kjos <tkjos@android.com>; Martijn Coenen
><maco@android.com>; Joel Fernandes <joel@joelfernandes.org>;
>devel@driverdev.osuosl.org; dri-devel@lists.freedesktop.org;
>linaro-mm-sig@lists.linaro.org; linux-kernel@vger.kernel.org
>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@redhat.com]
>>> Sent: Thursday, December 20, 2018 2:10 AM
>>> To: Zengtao (B) <prime.zeng@hisilicon.com>;
>sumit.semwal@linaro.org
>>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>; Arve
>Hjønnevåg
>>> <arve@android.com>; Todd Kjos <tkjos@android.com>; Martijn
>Coenen
>>> <maco@android.com>; Joel Fernandes <joel@joelfernandes.org>;
>>> devel@driverdev.osuosl.org; dri-devel@lists.freedesktop.org;
>>> linaro-mm-sig@lists.linaro.org; linux-kernel@vger.kernel.org
>>> 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/2018-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.

>
>>>
>>>> Signed-off-by: Zeng Tao <prime.zeng@hisilicon.com>
>>>> ---
>>>>    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
>>>>
>>