Patches Proceed For Disabling Radeon AGP GART, Deprecating TTM AGP
Written by Michael Larabel in Radeon on 16 May 2020 at 07:33 PM EDT. 36 Comments
RADEON --
Several days back was the proposal to "remove AGP support" from Radeon/Nouveau/TTM. This did formulate into a set of patches that would disable the AGP mode in the Radeon driver and deprecate the AGP code in TTM memory management. However, as was pointed out in the ensuing discussion, AGP graphics cards will still be operable on Linux with this level of deprecation by using the PCI GART mode.

Patches sent out after that original proposal include the Radeon disabling of AGP by default but the PCI GART functionality will still work. This is similar to Radeon having previously disabled the AGP mode on the POWER architecture due to bugs. There is the potential for negative performance implications from this change but no hard numbers appear to be brought up yet.

Besides the Radeon DRM driver disabling the AGP mode by default, a second patch deprecates the AGP code in TTM, the memory management code used by the Radeon driver and others. Besides marking it as deprecated, the TTM AGP code is now concealed by a DRM_TTM_AGP Kconfig option that defaults to disabled. That patch does also note that while the AGP GART code is less reliable than PCI GART, it can be faster in some cases. But if you are still pushing an AGP graphics card in 2020, it may be time to upgrade your system especially if you are running modern software/kernels.


As of writing this code hasn't yet been queued up in DRM-Next for Linux 5.8 and that cut-off is coming up quickly, so it's possible this AGP deprecation might not take place until Linux 5.9.
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