Only export struct fb_info.fix.smem_start if that is required by the
user and the memory does not come from vmalloc().

Setting struct fb_info.fix.smem_start breaks systems where DMA
memory is backed by vmalloc address space. An example error is
shown 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 #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

Additionally, DMA memory is assumed to by contiguous in physical
address space, which is not guaranteed by vmalloc().

Resolve this by checking the module flag drm_leak_fbdev_smem when
DRM allocated the instance of struct fb_info. Fbdev-dma then only
sets smem_start only if required (via FBINFO_HIDE_SMEM_START). Also
guarantee that the framebuffer is not located in vmalloc address
space.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reported-by: Peng Fan (OSS) <peng.fan@oss.nxp.com>
Closes: https://lore.kernel.org/dri-devel/20240604080328.4024838-1-peng.fan@oss.nxp.com/Reported-by: Geert Uytterhoeven <geert+renesas@glider.be>
Closes: https://lore.kernel.org/dri-devel/CAMuHMdX3N0szUvt1VTbroa2zrT1Nye_VzPb5qqCZ7z5gSm7HGw@mail.gmail.com/
Fixes: a51c7663 ("drm/fb-helper: Consolidate CONFIG_DRM_FBDEV_LEAK_PHYS_SMEM")
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: <stable@vger.kernel.org> # v6.4+
Link: https://patchwork.freedesktop.org/patch/msgid/20240617152843.11886-1-tzimmermann@suse.de