[PATCH v4] video: hyperv: hyperv_fb: Use physical memory for fb on HyperV Gen 1 VMs.

[Michael Kelley]

From: Wei Hu <weh at microsoft.com> Sent: Sunday, December 8, 2019 11:58 PM
> 
> On Hyper-V, Generation 1 VMs can directly use VM's physical memory for
> their framebuffers. This can improve the efficiency of framebuffer and
> overall performence for VM. The physical memory assigned to framebuffer
> must be contiguous. We use CMA allocator to get contiguouse physicial
> memory when the framebuffer size is greater than 4MB. For size under
> 4MB, we use alloc_pages to achieve this.
> 
> To enable framebuffer memory allocation from CMA, supply a kernel
> parameter to give enough space to CMA allocator at boot time. For
> example:
>     cma=130m
> This gives 130MB memory to CAM allocator that can be allocated to
> framebuffer. If this fails, we fall back to the old way of using
> mmio for framebuffer.
> 
> Reported-by: kbuild test robot <lkp at intel.com>
> Signed-off-by: Wei Hu <weh at microsoft.com>
> ---
>     v2: Incorporated review comments form hch at lst.de, Michael Kelley and
>     Dexuan Cui
>     - Use dma_alloc_coherent to allocate large contiguous memory
>     - Use phys_addr_t for physical addresses
>     - Corrected a few spelling errors and minor cleanups
>     - Also tested on 32 bit Ubuntu guest
>     v3: Fixed a build issue reported by kbuild test robot and incorported
>     some review comments from Michael Kelley
>     - Add CMA check to avoid link failure
>     - Fixed small memory leak introduced by alloc_apertures
>     - Cleaned up so code
>     v4: Removed request_pages variable as it is no longer needed
> 
>  drivers/video/fbdev/Kconfig     |   1 +
>  drivers/video/fbdev/hyperv_fb.c | 182 +++++++++++++++++++++++++-------
>  2 files changed, 144 insertions(+), 39 deletions(-)
> 

Reviewed-by: Michael Kelley <mikelley at microsoft.com>