The cards are not all the same - neither are the radeon drivers.
- Radeon driver covers most non-Radeon HD products.
- AMD Radeon X850/X800 and below.
- Radeon_hd driver is for the Radeon R500-family and higher products:
- AMD Radeon X1200 -> Radeon RX Vega 64
- NOTE: AMD Radeon X1900 series not supported at this time.
The RX 580 is not the RX 480. A misconception. The RX 580 handles the 4K60 (versus 4K30) resolution.
- The RX 460 is supported by the driver. Bug report it w/syslog attached.
- The RX 580 is not supported by the radeon_hd driver as of 7/17/2019.
So, a hit-or-miss with so many product variants with driver support. Remember, this is a hobby project
for the core developers (i.e. they got families/kids, school, paid work, bills, life, etc) so talk to them on IRC and post those bug reports.