Investigate DDR200 bus mode for sdhci-msm #867
Description
Platform: pretty much all of them?
Is your feature request related to a problem? Please describe.
Times and times again people have been complaining that the external storage is somewhat slow.
And it always seemed a bit bitchy given these aren't consoles, and they don't have pcie lines out.. Yet with external dedicated sd readers they could report quite better results (well at least on the most expensive cards).
And so what could be the internal bottleneck, that even after 10 years speed basically didn't budge even a little?
After a lot of headbanging this seems obviously that UHS-I taps out at SDR104 (which be it the file system or phy layer overhead, should equal to a data rate of about ~90 MB/s maximum).
Describe the solution you'd like
Try to see if you can program the mmc controller to work with DDR200 (samsung microsds recommended)
https://github.com/CTCaer/switch-l4t-kernel-4.9/blob/linux-dev/drivers/mmc/host/sdhci-tegra.c
Describe alternatives you've considered
Mixed in those commits there's also this which I believe to be a minor optimization in comparison.
Additional context
There's no markings that I'm aware of on the cards slot itself, but after much looking around I think I had a stroke of luck with https://www.jae.com/en/connectors/series/detail/id=64207&type_code=T1100
AFAICT it's literally the only sim+sim/sd combo still on sale worldwide (I don't know if others couldn't have existed in the past, but even when I tried to look for non-dual-sim combos I could only notice a couple).