With the patch, when playing problematic videos, I get a black screen instead
of a partial display with green artifacts.

Also, with and without the patch, dmesg catches the following when playing the
problematic videos (I should have had a look previously):
[76261.125581] [drm:radeon_uvd_cs_parse [radeon]] *ERROR* Handle 0x8fd80001
already in use!
[76261.125594] [drm:radeon_cs_ioctl [radeon]] *ERROR* Invalid command stream !
[76261.126059] [drm:radeon_uvd_cs_parse [radeon]] *ERROR* Handle 0x8fd80001
already in use!
[76261.126072] [drm:radeon_cs_ioctl [radeon]] *ERROR* Invalid command stream !
[76261.126441] [drm:radeon_uvd_cs_parse [radeon]] *ERROR* Handle 0x8fd80001
already in use!
[76261.126452] [drm:radeon_cs_ioctl [radeon]] *ERROR* Invalid command stream !