Am 18.06.24 um 07:01 schrieb Pierre Ossman:
On 17/06/2024 20:18, Christian König wrote:
Am 17.06.24 um 19:18 schrieb Pierre Ossman:
On 17/06/2024 18:09, Michel Dänzer wrote:
Can I know whether it is needed or not? Or should I be cautious
and always do it?
Assuming GBM in the X server uses the GPU HW driver, I'd say it
shouldn't be needed.
It does not (except the driver libgbm loads). We're trying to use
this in Xvnc, so it's all CPU. We're just trying to make sure the
applications can use the full power of the GPU to render their stuff
before handing it over to the X server. :)
That whole approach won't work.
When you don't have a HW driver loaded or at least tell the client
that it should render into a linear buffer somehow then the data in
the buffer will be tilled in a hw specific format.
As far as I know you can't read that vendor agnostic with the CPU,
you need the hw driver for that.
I'm confused. What's the goal of the GBM abstraction and specifically
gbm_bo_map() if it's not a hardware-agnostic way of accessing buffers?
There is no hardware agnostic way of accessing buffers which contain hw
specific data.
You always need a hw specific backend for that or use the linear flag
which makes the data hw agnostic.
In practice, we are getting linear buffers. At least on Intel and AMD
GPUs. Nvidia are being a bit difficult getting GBM working, so we
haven't tested that yet.
That's either because you have a linear buffer for some reason or the
hardware specific gbm backend has inserted a blit as Michel described.
I see there is the GBM_BO_USE_LINEAR flag. We have not used it yet, as
we haven't seen a need for it. What is the effect of that? Would it
guarantee what we are just lucky to see at the moment?
Michel and/or Marek need to answer that. I'm coming from the kernel side
and maintaining the DMA-buf implementation backing all this, but I'm not
an expert on gbm.
Regards,
Christian.
Regards
