Hello Thomas,
On 5/5/22 09:29, Thomas Zimmermann wrote:
[snip]
>> static void simplefb_destroy(struct fb_info *info)
>> {
>> struct simplefb_par *par = info->par;
>> @@ -94,6 +98,8 @@ static void simplefb_destroy(struct fb_info *info)
>> if (info->screen_base)
>> iounmap(info->screen_base);
>>
>> + framebuffer_release(info);
>> +
>> if (mem)
>> release_mem_region(mem->start, resource_size(mem));
>
> The original problem with fbdev hot-unplug was that vmwgfx needed the
> framebuffer region to be released. If we release it only after userspace
> closed it's final file descriptor, vmwgfx could have already failed.
>
> I still don't fully get why this code apparently works or at least
> doesn't blow up occasionally. Any ideas?
>
I believe that vmwgfx doesn't fail to probe (or any other DRM driver)
only when there are not user-space processes with a fbdev node opened
since otherwise as you said the memory wouldn't be released yet.
unregister_framebuffer() is called from the driver's .remove handler
and that decrement the fb_info refcount, so if reaches zero it will
call to the fb fops .destroy() handler and release the I/O memory.
In other words, in most cases (i.e: only fbcon bound to the fbdev)
the driver's removal/ device unbind and the memory release will be
at the same time.
--
Best regards,
Javier Martinez Canillas
Linux Engineering
Red Hat
