RE: [bug report] video: hyperv: hyperv_fb: Use physical memory for fb on HyperV Gen 1 VMs.

[Wei Hu <weh@microsoft.com>]

Hello Dan,

> -----Original Message-----> 
> Hello Wei Hu,
> 
> The patch 3a6fb6c4255c: "video: hyperv: hyperv_fb: Use physical memory for
> fb on HyperV Gen 1 VMs." from Dec 9, 2019, leads to the following static
> checker warning:
> 
> 	drivers/video/fbdev/hyperv_fb.c:991 hvfb_get_phymem()
> 	error: 'vmem' came from dma_alloc_coherent() so we can't do
> virt_to_phys()
> 
> drivers/video/fbdev/hyperv_fb.c
>    960  static phys_addr_t hvfb_get_phymem(struct hv_device *hdev,
>    961                                     unsigned int request_size)
>    962  {
>    963          struct page *page = NULL;
>    964          dma_addr_t dma_handle;
>    965          void *vmem;
>    966          phys_addr_t paddr = 0;
>    967          unsigned int order = get_order(request_size);
>    968
>    969          if (request_size == 0)
>    970                  return -1;
>    971
>    972          if (order < MAX_ORDER) {
>    973                  /* Call alloc_pages if the size is less than 2^MAX_ORDER */
>    974                  page = alloc_pages(GFP_KERNEL | __GFP_ZERO, order);
>    975                  if (!page)
>    976                          return -1;
>    977
>    978                  paddr = (page_to_pfn(page) << PAGE_SHIFT);
>    979          } else {
>    980                  /* Allocate from CMA */
>    981                  hdev->device.coherent_dma_mask = DMA_BIT_MASK(64);
>    982
>    983                  vmem = dma_alloc_coherent(&hdev->device,
>    984                                            round_up(request_size, PAGE_SIZE),
>    985                                            &dma_handle,
>    986                                            GFP_KERNEL | __GFP_NOWARN);
>    987
>    988                  if (!vmem)
>    989                          return -1;
>    990
>    991                  paddr = virt_to_phys(vmem);
> 
> Pretty straight forward that the static checker is right but I can't give you any
> hints how to fix it.
> 

Thanks for reporting this. Would you let me know how I can reproduce this warning or
Error message? The build on my side runs fine without such message.

Thanks,
Wei