Enabling CONFIG_GART_IOMMU by default?

[Tomáš Trnka]

Hello,

I have a PCI-based SATA controller (Sil3124) that chokes on PCI DAC 
addressing, so I have to force 32-bit addressing through an IOMMU. Sadly, the 
stock Fedora kernel falls back to SWIOTLB on this machine, which is both 
slower (though I haven't benchmarked it) and unreliable (several times I've 
seen the SWIOTLB overflow and go boom).

Apparently, all I need is the AMD GART-based IOMMU implementation 
(CONFIG_GART_IOMMU) that is currently disabled by Fedora. This means I 
currently have to rebuild the kernel every time to re-enable it.

Is there any particular reason why this is disabled in Fedora (upstream 
Kconfig default is enabled)? Given that there is probably a non-negligible 
fraction of machines that could benefit from the GART IOMMU and the kernel 
size impact is minimal, would it be possible to restore the upstream default?

Best regards,

Tomáš Trnka