On 3/3/22 21:58, Thomas Zimmermann wrote:

The fbdev mmap function fb_mmap() unconditionally overrides the
driver's implementation if deferred I/O has been activated. This
makes it hard to implement mmap with anything but a vmalloc()'ed
software buffer. That is specifically a problem for DRM, where
video memory is maintained by a memory manager.

Leave the mmap handling to drivers and expect them to call the
helper for deferred I/O by thmeselves.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
---

[snip]

 
+	/*
+	 * FB deferred I/O want you to handle mmap in your drivers. At a
+	 * minimum, point struct fb_ops.fb_mmap to fb_deferred_io_mmap().
+	 */
+	if (WARN_ON_ONCE(info->fbdefio))
+		return -ENODEV;
+

Maybe part of that comment could be printed as a WARN_ON_ONCE() message ?

Regardless, the patch looks good to me:

Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>

-- 
Best regards,

Javier Martinez Canillas
Linux Engineering
Red Hat