[PATCH v6 3/3] arm64: dts: rockchip: Add Radxa CM5 IO Board

[Jimmy Hon]

On Wed, Nov 5, 2025 at 9:31 PM Dragan Simic <dsimic at manjaro.org> wrote:

[ snip ]

>
> With all that in mind, we should specify "no-mmc" here, because
> we're describing a microSD slot, instead of describing some hybrid
> MMC/microSD slot.  That also explains why the adapter sold by Radxa
> is described as not to be used with microSD card slots on SBCs.  I'd
> also like to hear is this adapter/eMMC chip combo recognized by the
> kernel when "no-mmc" is specified; it should fail.
>
> Actually, not specifying "no-mmc" here may result in some unforeseen
> issues with some (or perhaps many?) microSD cards, because the MMC
> drivers will treat them as MMC-capable devices and try to initialize
> them as such, which may cause all kinds of issues.  In fact, I'm not
> really sure that the MMC drivers are actually implemented in a way
> that avoids all possible issues with the storage controllers that
> are capable of both SD and MMC modes when neither of "no-sd" and
> "no-mmc" is specified in their DT nodes.

Hybrid MMC and SD slots are pretty normal on USB card readers. So it's
normal for the host controller to figure out what kind of card is in
the slot.
https://uditagarwal.in/understanding-sd-sdio-and-mmc-interface/

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6ae3e537eab9f560b516b001eb89f0cd568bdced
was the commit that introduced the device tree properties. By the
wording of the commit message, these device tree properties are used
to indicate to the driver if the host controller hardware is capable
of MMC initialization or SD initialization.

Since the host controller in the RK3588 is capable of all the modes,
these properties do not need to be specified.

Since Radxa has the eMMC to uSD adapter, it makes sense Radxa would
want to configure their microSD card slot on their boards to be a
hybrid SD/MMC slot.

Now, the more fun question is if the adapter can handle eMMC HS200
using the 4-bit bus?

Jimmy