Re: [PATCH] ati-vga: Fix framebuffer mapping by using hardware-correct aperture sizes

["Chad Jablonski" <chad@jablonski.xyz>]

>
> I'm not saying the 64MB alignment is not correct (I don't know what is 
> correct and assuming the Xorg driver was tested with real cards it's 
> possible this assumption holds) but maybe it comes from having a 64MB VRAM 
> BAR that contains twice the size of actual VRAM including the AGP window 
> which also satisfies the 32MB alignment for VRAM, so the commit message 
> may nees to be adjusted to say that instead of something not supported by 
> documentation. Do you have any PCI cards? There were PCI versions of 
> these. I wonder if they also have the same VRAM BAR. If not then no 
> problem, we can go with what works for known drivers.
>

Unfortunately I don't have a PCI Rage 128. They actually seem to be somewhat
rare compared to the AGP versions!

Testing results from two Rage 128 AGP cards:

Card                      VRAM    PCI BAR0   CONFIG_MEMSIZE  CONFIG_APER_SIZE  AGP_APER_OFFSET
-----------------------   ----    --------   --------------  ----------------  ---------------
Rage 128 Pro Ultra TF     32MB    64MB       0x02000000      0x02000000        0x02000000
Rage 128 RF/SG AGP        16MB    64MB       0x01000000      0x02000000        0x02000000


* PCI BAR0 (Region 0) is fixed at 64MB for both cards, regardless of actual
  VRAM size.

* CONFIG_MEMSIZE correctly reports actual VRAM size (32MB and 16MB).

* CONFIG_APER_SIZE is fixed at 32MB (0x02000000) on both cards, regardless
  of:
   - Actual VRAM size
   - AGP enabled/disabled status
   - AGP_APER_SIZE configuration (tested with 8MB AGP enabled)

   This directly contradicts the Rage 128 Pro Register Reference Guide
   (pg. 3-202) which states: "Size of linear apertures (both 0 and 1).
   This includes both the frame buffer image and the AGP system memory
   image area."

* AGP_APER_OFFSET is also fixed at 32MB (0x02000000) on both cards. On the
  16MB card, this creates a 16MB gap between the end of framebuffer and the
  start of the AGP window.

So for Rage 128, CONFIG_APER_SIZE should be set to a fixed 32MB value, not
dynamically calculated from CONFIG_MEMSIZE + AGP space as the documentation
suggests and as was previously implemented by me 😬.

I'm less sure about the Radeon and your additional context around the Radeon
on PowerPC makes me very nervous to change it right now. Especially given I
have a single example of that card and it's for a PC. I think it makes more
sense to leave the behavior of CONFIG_APER_SIZE for that card unchanged.

I will send a v2 patch that:
  * Sets Rage 128 CONFIG_APER_SIZE to 32MB
  * Updates the commit message to reflect that
  * Leaves Radeon unchanged (half of the vram_size)
  * Addresses the style issues