[PATCH v2 1/9] drm/gem-vram: Support pinning buffers to current location

[Gerd Hoffmann]

On Wed, Jun 12, 2019 at 10:29:29AM +0200, Thomas Zimmermann wrote:
> Hi
> 
> Am 12.06.19 um 10:13 schrieb Gerd Hoffmann:
> > On Tue, Jun 11, 2019 at 03:03:36PM +0200, Thomas Zimmermann wrote:
> >> Pinning a buffer prevents it from being moved to a different memory
> >> location. For some operations, such as buffer updates, it is not
> >> important where the buffer is located. Setting the pin function's
> >> pl_flag argument to 0 will pin the buffer to whereever it is stored.
> >>
> >> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
> >> ---
> >>  drivers/gpu/drm/drm_gem_vram_helper.c | 12 ++++++++----
> >>  1 file changed, 8 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/drm_gem_vram_helper.c b/drivers/gpu/drm/drm_gem_vram_helper.c
> >> index 42ad80888df7..214f54b8920b 100644
> >> --- a/drivers/gpu/drm/drm_gem_vram_helper.c
> >> +++ b/drivers/gpu/drm/drm_gem_vram_helper.c
> >> @@ -224,7 +224,9 @@ EXPORT_SYMBOL(drm_gem_vram_offset);
> >>   *
> >>   * Pinning a buffer object ensures that it is not evicted from
> >>   * a memory region. A pinned buffer object has to be unpinned before
> >> - * it can be pinned to another region.
> >> + * it can be pinned to another region. If the pl_flag argument is 0,
> >> + * the buffer is pinned at its current location (video RAM or system
> >> + * memory).
> >>   *
> >>   * Returns:
> >>   * 0 on success, or
> >> @@ -242,7 +244,9 @@ int drm_gem_vram_pin(struct drm_gem_vram_object *gbo, unsigned long pl_flag)
> >>  	if (gbo->pin_count)
> >>  		goto out;
> >>  
> >> -	drm_gem_vram_placement(gbo, pl_flag);
> >> +	if (pl_flag)
> >> +		drm_gem_vram_placement(gbo, pl_flag);
> >> +
> >>  	for (i = 0; i < gbo->placement.num_placement; ++i)
> >>  		gbo->placements[i].flags |= TTM_PL_FLAG_NO_EVICT;
> >>  
> >> @@ -691,7 +695,7 @@ int drm_gem_vram_driver_gem_prime_pin(struct drm_gem_object *gem)
> >>  {
> >>  	struct drm_gem_vram_object *gbo = drm_gem_vram_of_gem(gem);
> >>  
> >> -	return drm_gem_vram_pin(gbo, DRM_GEM_VRAM_PL_FLAG_VRAM);
> >> +	return drm_gem_vram_pin(gbo, 0);
> 
> The only use case for these Prime helpers is fbdev console emulation. I
> have another patch set that replaces the ast and mgag200 consoles with
> generic code. During the console updates it temporarily pins the BO via
> this Prime funcation, which might move the BO into scarce VRAM
> unnecessarily.

Ok, if the pin is temporary only for the update this should be fine.

> Can we leave it like this and add a comment explaining
> the decision?

Yes, a comment is a good idea.

cheers,
  Gerd