Hi Jonas,
On 4/8/24 23:06, Jonas Karlman wrote:
eMMC nodes in linux device tree files typically only contain a mmc-hs400
prop to signal support for both HS400 and HS200. However, U-Boot require
an explicit mmc-hs200 prop to signal support for the HS200 mode.
> Fix this by follow linux and imply HS200 cap when HS400 cap is signaled
using a mmc-hs400 prop.
Technically speaking, the DT binding should be the one and only source
of truth and should be implementation-agnostic.
There it says:
"""
mmc-hs400-1_2v:
$ref: /schemas/types.yaml#/definitions/flag
description:
eMMC HS400 mode (1.2V I/O) is supported.
mmc-hs400-1_8v:
$ref: /schemas/types.yaml#/definitions/flag
description:
eMMC HS400 mode (1.8V I/O) is supported.
"""
So I'd say, the DTs should be fixed to add mmc-hs200 as well wherever it
makes sense.
The point of the DT/DT binding is to be system-agnostic and
representative of the **HW** implementation. At least that's what the DT
people want it to be.
If the eMMC standard doesn't allow to have HS400 without HS200, then I
think this change is acceptable as is, because it is the reality of the
HW standard. Couldn't find this implied in the standard though (but I
just skimmed through).
It's also quite surprising, as it's not because the eMMC works with
HS400 that it necessarily does with HS200 or that it's desired (EMI,
signal integrity/stability, etc...)?
Now, it wouldn't be the first time U-Boot follows whatever is done in
Linux, so... up to you/the maintainers :)
Reviewed-by: Quentin Schulz <quentin.sch...@theobrma-systems.com>
Cheers,
Quentin
