drm/fbdev-dma: fix getting smem_start

If 'info->screen_buffer' locates in vmalloc address space, virt_to_page
will not be able to get correct results. With CONFIG_DEBUG_VM and
CONFIG_DEBUG_VIRTUAL enabled on ARM64, there is dump below:
[    3.536043] ------------[ cut here ]------------
[    3.540716] virt_to_phys used for non-linear address: 000000007fc4f540 (0xffff800086001000)
[    3.552628] WARNING: CPU: 4 PID: 61 at arch/arm64/mm/physaddr.c:12 __virt_to_phys+0x68/0x98
[    3.565455] Modules linked in:
[    3.568525] CPU: 4 PID: 61 Comm: kworker/u12:5 Not tainted 6.6.23-06226-g4986cc3e1b75-dirty torvalds#250
[    3.577310] Hardware name: NXP i.MX95 19X19 board (DT)
[    3.582452] Workqueue: events_unbound deferred_probe_work_func
[    3.588291] pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[    3.595233] pc : __virt_to_phys+0x68/0x98
[    3.599246] lr : __virt_to_phys+0x68/0x98
[    3.603276] sp : ffff800083603990
[    3.677939] Call trace:
[    3.680393]  __virt_to_phys+0x68/0x98
[    3.684067]  drm_fbdev_dma_helper_fb_probe+0x138/0x238
[    3.689214]  __drm_fb_helper_initial_config_and_unlock+0x2b0/0x4c0
[    3.695385]  drm_fb_helper_initial_config+0x4c/0x68
[    3.700264]  drm_fbdev_dma_client_hotplug+0x8c/0xe0
[    3.705161]  drm_client_register+0x60/0xb0
[    3.709269]  drm_fbdev_dma_setup+0x94/0x148

So add a check 'is_vmalloc_addr'.

Fixes: b79fe9a ("drm/fbdev-dma: Implement fbdev emulation for GEM DMA helpers")
Signed-off-by: Peng Fan <peng.fan@nxp.com>

drivers/gpu/drm/drm_fbdev_dma.c

@@ -130,7 +130,12 @@ static int drm_fbdev_dma_helper_fb_probe(struct drm_fb_helper *fb_helper,
 		info->flags |= FBINFO_READS_FAST; /* signal caching */
 	info->screen_size = sizes->surface_height * fb->pitches[0];
 	info->screen_buffer = map.vaddr;
-	info->fix.smem_start = page_to_phys(virt_to_page(info->screen_buffer));
+
+	if (is_vmalloc_addr(info->screen_buffer))
+		info->fix.smem_start = page_to_phys(vmalloc_to_page(info->screen_buffer));
+	else
+		info->fix.smem_start = page_to_phys(virt_to_page(info->screen_buffer));
+
 	info->fix.smem_len = info->screen_size;
 
 	return 0;