radeondrm

make radeondrm(1) work with iMac 11,1
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README (975B)

      1   iMac 11,1 radeondrm(4)
      2 ========================
      3 
      4 The ATI Radeon HD4850M in my 2009 iMac 11,1 does not work with
      5 radeondrm(4) because of two distinct problems.
      6 Both Linux (https://bugs.freedesktop.org/show_bug.cgi?id=98046) and OpenBSD
      7 have this issue.
      8 
      9 Latest Release: 72 on January 22 2023
     10 Install:        # cd /sys/dev/pci/drm && patch < imac_11_1_radeondrm.diff
     11 
     12 There are two distinct problems:
     13 
     14 
     15  1 - Black screen
     16 -----------------
     17 
     18 The first problem is the display goes black, with backlight off, when
     19 radeondrm(4) initializes the GPU. The fix for this issue is similar to
     20 the workaround added for iMac 10,1 machines.
     21 
     22 The `atombios_encoders.c` hunk of the diff fixes this issue.
     23 
     24 
     25  2 - PLL computation
     26 --------------------
     27 
     28 There is something wrong with the new PLL code that was introduced around
     29 2012 that causes the PLL computation to be incorrect for this board.
     30 Reverting that change fixes this issue.
     31 
     32 The `radeon_display.c` hunk of the diff fixes this issue.