Re: [PATCH v3 1/3] drm: add prime helpers

[Aaron Plattner <aplattner@nvidia.com>]

On 06/18/2013 04:08 PM, Laurent Pinchart wrote:
> Hi Aaron,
>
> A bit late, but here's a small question.
>
> On Tuesday 15 January 2013 12:47:42 Aaron Plattner wrote:
>> Instead of reimplementing all of the dma_buf functionality in every driver,
>> create helpers drm_prime_import and drm_prime_export that implement them in
>> terms of new, lower-level hook functions:
>>
>>    gem_prime_pin: callback when a buffer is created, used to pin buffers into
>> GTT gem_prime_get_sg_table: convert a drm_gem_object to an sg_table for
>> export gem_prime_import_sg_table: convert an sg_table into a drm_gem_object
>> gem_prime_vmap, gem_prime_vunmap: map and unmap an object
>>
>> These hooks are optional; drivers can opt in by using drm_gem_prime_import
>> and drm_gem_prime_export as the .gem_prime_import and .gem_prime_export
>> fields of struct drm_driver.
>>
>> v2:
>> - Drop .begin_cpu_access.  None of the drivers this code replaces
>> implemented it.  Having it here was a leftover from when I was trying to
>> include i915 in this rework.
>> - Use mutex_lock instead of mutex_lock_interruptible, as these three drivers
>> did.  This patch series shouldn't change that behavior.
>> - Rename helpers to gem_prime_get_sg_table and gem_prime_import_sg_table.
>>    Rename struct sg_table* variables to 'sgt' for clarity.
>> - Update drm.tmpl for these new hooks.
>>
>> v3:
>> - Pass the vaddr down to the driver.  This lets drivers that just call
>> vunmap on the pointer avoid having to store the pointer in their GEM
>> private structures. - Move documentation into a /** DOC */ comment in
>> drm_prime.c and include it in drm.tmpl with a !P line.  I tried to use !F
>> lines to include documentation of the individual functions from drmP.h, but
>> the docproc / kernel-doc scripts barf on that file, so hopefully this is
>> good enough for now.
>> - apply refcount fix from commit be8a42ae60addd8b6092535c11b42d099d6470ec
>>    ("drm/prime: drop reference on imported dma-buf come from gem")
>>
>> Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
>> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
>> Cc: David Airlie <airlied@linux.ie>
>> ---
>>   Documentation/DocBook/drm.tmpl |   4 +
>>   drivers/gpu/drm/drm_prime.c    | 186 +++++++++++++++++++++++++++++++++++++-
>>   include/drm/drmP.h             |  12 +++
>>   3 files changed, 201 insertions(+), 1 deletion(-)
>
> [snip]
>
>> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
>> index 7f12573..366910d 100644
>> --- a/drivers/gpu/drm/drm_prime.c
>> +++ b/drivers/gpu/drm/drm_prime.c
>
> [snip]
>
>> +/**
>> + * DOC: PRIME Helpers
>> + *
>> + * Drivers can implement @gem_prime_export and @gem_prime_import in terms
>> of + * simpler APIs by using the helper functions @drm_gem_prime_export and
>> + * @drm_gem_prime_import.  These functions implement dma-buf support in
>> terms of + * five lower-level driver callbacks:
>> + *
>> + * Export callbacks:
>> + *
>> + *  - @gem_prime_pin (optional): prepare a GEM object for exporting
>> + *
>> + *  - @gem_prime_get_sg_table: provide a scatter/gather table of pinned
>> pages + *
>> + *  - @gem_prime_vmap: vmap a buffer exported by your driver
>> + *
>> + *  - @gem_prime_vunmap: vunmap a buffer exported by your driver
>> + *
>> + * Import callback:
>> + *
>> + *  - @gem_prime_import_sg_table (import): produce a GEM object from
>> another + *    driver's scatter/gather table
>> + */
>> +
>> +struct dma_buf *drm_gem_prime_export(struct drm_device *dev,
>> +				     struct drm_gem_object *obj, int flags)
>> +{
>> +	if (dev->driver->gem_prime_pin) {
>> +		int ret = dev->driver->gem_prime_pin(obj);
>> +		if (ret)
>> +			return ERR_PTR(ret);
>> +	}
>> +	return dma_buf_export(obj, &drm_gem_prime_dmabuf_ops, obj->size,
>> +			      0600);
>
> Why do you use 0600 instead of the flags passed by the caller ?

Because I copied & pasted it from i915_gem_prime_export prior to commit 
5b42427fc38ecb9056c4e64deaff36d6d6ba1b67 and didn't notice until you 
pointed it out just now.

>> +}
>> +EXPORT_SYMBOL(drm_gem_prime_export);


-- 
Aaron