Re: [Intel-gfx] [PATCH 1/3] drm/i915: Set I915_BO_ALLOC_USER for framebuffer

["Das, Nirmoy" <nirmoy.das@linux.intel.com>]

Hi Matt,

On 3/6/2023 1:25 PM, Matthew Auld wrote:
> On 06/03/2023 12:07, Nirmoy Das wrote:
>> Framebuffer is exposed to userspace so set I915_BO_ALLOC_USER
>> flag for it. This also make sure that ttm allocates offset
>> for lmem objects.
>>
>> Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
>> ---
>>   drivers/gpu/drm/i915/display/intel_dpt.c           | 4 +++-
>>   drivers/gpu/drm/i915/display/intel_fbdev.c         | 3 ++-
>>   drivers/gpu/drm/i915/display/intel_plane_initial.c | 3 ++-
>>   3 files changed, 7 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_dpt.c 
>> b/drivers/gpu/drm/i915/display/intel_dpt.c
>> index ad1a37b515fb..2e6238881860 100644
>> --- a/drivers/gpu/drm/i915/display/intel_dpt.c
>> +++ b/drivers/gpu/drm/i915/display/intel_dpt.c
>> @@ -254,7 +254,9 @@ intel_dpt_create(struct intel_framebuffer *fb)
>>         size = round_up(size * sizeof(gen8_pte_t), I915_GTT_PAGE_SIZE);
>>   -    dpt_obj = i915_gem_object_create_lmem(i915, size, 
>> I915_BO_ALLOC_CONTIGUOUS);
>> +    dpt_obj = i915_gem_object_create_lmem(i915, size,
>> +                          I915_BO_ALLOC_CONTIGUOUS |
>> +                          I915_BO_ALLOC_USER);
>
> AFAICT this is just some driver internal stuff for display page-table, 
> which gets mapped through GGTT or something, and is not the actual fb. 
> Is it really exposed to the user?


I misunderstood this for something else. I will remove this.

>
>>       if (IS_ERR(dpt_obj) && i915_ggtt_has_aperture(to_gt(i915)->ggtt))
>>           dpt_obj = i915_gem_object_create_stolen(i915, size);
>>       if (IS_ERR(dpt_obj) && !HAS_LMEM(i915)) {
>> diff --git a/drivers/gpu/drm/i915/display/intel_fbdev.c 
>> b/drivers/gpu/drm/i915/display/intel_fbdev.c
>> index 3659350061a7..98ae3a3a986a 100644
>> --- a/drivers/gpu/drm/i915/display/intel_fbdev.c
>> +++ b/drivers/gpu/drm/i915/display/intel_fbdev.c
>> @@ -163,7 +163,8 @@ static int intelfb_alloc(struct drm_fb_helper 
>> *helper,
>>       obj = ERR_PTR(-ENODEV);
>>       if (HAS_LMEM(dev_priv)) {
>>           obj = i915_gem_object_create_lmem(dev_priv, size,
>> -                          I915_BO_ALLOC_CONTIGUOUS);
>> +                          I915_BO_ALLOC_CONTIGUOUS |
>> +                          I915_BO_ALLOC_USER);
>>       } else {
>>           /*
>>            * If the FB is too big, just don't use it since fbdev is 
>> not very
>> diff --git a/drivers/gpu/drm/i915/display/intel_plane_initial.c 
>> b/drivers/gpu/drm/i915/display/intel_plane_initial.c
>> index bb6ea7de5c61..4a3680f6a3f5 100644
>> --- a/drivers/gpu/drm/i915/display/intel_plane_initial.c
>> +++ b/drivers/gpu/drm/i915/display/intel_plane_initial.c
>> @@ -110,7 +110,8 @@ initial_plane_vma(struct drm_i915_private *i915,
>>           size * 2 > i915->dsm.usable_size)
>>           return NULL;
>>   -    obj = i915_gem_object_create_region_at(mem, phys_base, size, 0);
>> +    obj = i915_gem_object_create_region_at(mem, phys_base, size,
>> +                           I915_BO_ALLOC_USER);
>
> ALLOC_USER has the side effect of also zeroing the memory underneath, 
> IIRC. However this here is the pre-allocated fb (will have some boot 
> logo stuff), so we shouldn't ever clear it.


This was my concern.  I wonder if there is any other better way than to 
use a temp buffer to copy the pre-allocated content and put it back 
after getting i915_gem_object_create_region_at().


Regards,

Nirmoy


>
>>       if (IS_ERR(obj))
>>           return NULL;