How to share texture memory between CPU/GPU for firefly's/rk3288 fbdev Mali-T764

Sorry, forgot to reply to your other questions:

Here is the RGBA_8888:

#define RGBA8888_FORMAT: 0x00000000010BB053

Regarding dma_buf: all you need is the file descriptor (int) for your dma_buf allocation.

Unfortunately there is no standard kernel interface to allocate dma_buf memory, so you will have to look into your platform's kernel sources.

Sometimes you've got a special IOCTL to get a handle to the framebuffer for example (There is one on Firefly for example).

I'm confused by what you're asking: are you on Linux FBDev or Android ?  The example code above is for fbdev only, if you're running on Android, you will have to use GraphicBuffer and EGL_NATIVE_BUFFER_ANDROID.

Sorry, forgot to reply to your other questions:

Here is the RGBA_8888:

#define RGBA8888_FORMAT: 0x00000000010BB053

Regarding dma_buf: all you need is the file descriptor (int) for your dma_buf allocation.

Unfortunately there is no standard kernel interface to allocate dma_buf memory, so you will have to look into your platform's kernel sources.

Sometimes you've got a special IOCTL to get a handle to the framebuffer for example (There is one on Firefly for example).

I'm confused by what you're asking: are you on Linux FBDev or Android ?  The example code above is for fbdev only, if you're running on Android, you will have to use GraphicBuffer and EGL_NATIVE_BUFFER_ANDROID.

Things are clear to me now, this will help me for sure.

I am on Linux FBDev for this question, so your example is exactly what gives me the right direction! Confusion comes from me because I also use libhybris in linux/ubuntu, making android libs (also your android libmali) available under linux, and actually that way i have access tp the video encoder/decoder hardware en hwcomposer.

You mention firefly has a special ioctl to get a handle to the framebuffer: can you give me more detail/ or code for this? You would help me out in saving a bit of kernel searching here.

Anyways, thanks for your answer again!

For the Firefly ioctl, it's in the 3.10 kernel and requires ION to be turned on:

https://bitbucket.org/T-Firefly/firefly-rk3288-kernel/src/f4d954d67f9e5689f1ddbbbd3050a8041424dd48/drivers/video/rockchip/rk_fb.c?at=master#cl-2469

T-Firefly / Firefly-RK3288-kernel / source / include / linux / rk_fb.h — Bitbucket

However the issue is that the fbdev Mali-T76x user-side binary driver available from malideveloper.arm.com is not specific to this kernel, or not even to Firefly but to any system with a Mali-T76x GPU.  So it doesn't know about this ioctl.  It would need to call it to get a DMA-BUF file descriptor from the display driver and then pass it to the kernel-side driver.

We're planning to fix support for DMA-BUF in fbdev in future drivers with a portable kernel patch, but unfortunately I can't yet tell when this will be available as we rely on other things to be released first.

Then to import a DMA-BUF file descriptor from the video decoder into the GPU, there is an extension for that:

https://www.khronos.org/registry/egl/extensions/EXT/EGL_EXT_image_dma_buf_import.txt

It is not yet enabled in our r5p0 driver but should be in a future version.  I'll post another message when this is released.

Thanks Guillaume! Your explanation is clear and helps me in digging further into dma-buf concept and usage.

For the rk3288 video decoder I can obtain the filedescriptor by using rockchips VPUMemGetFD() provided by their vpu memory allocator code: T-Firefly / Firefly-RK3288   / source  / frameworks / av / media / libstagefright / libvpu / common / vpu_mem_dmabuf.c —… Using libhybris I can access this android library - libvpu.

As dma-buf import is not yet supported in r5p0 driver I guess, for now, will have to use your android mali driver with libhybris - far from ideal.

I am of course very interested in your future release!

PS: for those interested, also found some interesting links related to dma_buf / ion stuff:

DMA buffer sharing in 3.3 [LWN.net]

The Android ION memory allocator [LWN.net]

Daeseok's Blog :: [ION] Sharing a buffer between kernel-space and user-space

ION Buffer sharing mechanism | :(){ :|:& };: