UHS SDR104 for Amlogic g12a/b & sm1 #26
Description
Hi, I was looking through a number of Amlogic dtbs to checkout the SDIO WiFi node properties. I noticed that most g12a/b & sm1 devices were either using cap-sd-highspeed or in a very few instances sd-uhs-sdr50 (sm1). The maximum frequency property is also limited to 50Mhz in most cases.
Is this because these devices fail SDIO tuning at frequencies above 75Mhz, so they can't use sdr50/sdr104?
I'm asking because I was previously using an s922x device in kernel 4.9 with Amlogic's SDIO driver, that was able to function with sdr104 at 200Mhz (+500Mbps WiFi speeds). Moving to kernel 5.15 there's a switch to this meson driver (AML's version). SDIO WiFi is functional but with this driver tuning fails above 67MHz, effectively limiting bandwidth to 1/3.
I wasn't sure how widespread this problem was, but based on the dtb's here, it must be common among g12a/b &sm1 devices. Newer SC2, A311D2 and S5 devices seem to work better with the meson driver, and function at sdr104 200Mhz. Comparing the AML 4.9 and Meson 5.15 drivers, the tuning process in the AML driver is more thorough, calibrating each data line individually. But I've not even had any luck manually applying the tuned SDIO properties from 4.9 to 5.15 and getting the SDIO node to function above 66Mhz.
Do you know anything more about this problem, or if there has been discussion about it anywhere?