Re: [PATCH] MdeModulePkg/SdMmcPciHcDxe: Fix DMA on SDHC v3 64-bit systems

["Cohen, Eugene" <eugene@hp.com>]

Ard,

> So before these changes, we were in the exact same situation, but since PC
> platforms never enable DMA above 4 GB in the first place, nobody ever
> noticed until we started running this code on arm64 platforms that have no
> 32-bit addressable DRAM to begin with.

Interesting - I did not realize that there were designs that were crazy enough to have no addressable DRAM below 4G.
 
> The obvious conclusion is that the driver should not set the
> EFI_PCI_IO_ATTRIBUTE_DUAL_ADDRESS_CYCLE attribute if the device does
> not support it, or, which seems to be our case, if the driver does not
> implement the 64-bit DMA mode that the driver does support. However,
> since there are platforms for which bounce buffering is not an option (since
> there is no 32-bit addressable memory to bounce to), this is not just a
> performance optimization, and so it would be useful to fix the code so it can
> drive all 64-bit DMA capable hardware.

Okay, that's a great reason - let's get V3 64b ADMA2 in!

Any objection to committing the original patch in the short term?

Thanks,

Eugene