[PATCH 1/2] mmc: Imply HS200 cap with mmc-hs400 prop to match linux

[Jaehoon Chung]

Hi,

> -----Original Message-----
> From: Quentin Schulz <quentin.schulz at theobroma-systems.com>
> Sent: Wednesday, April 10, 2024 12:27 AM
> To: Jonas Karlman <jonas at kwiboo.se>; Peng Fan <peng.fan at nxp.com>; Jaehoon Chung
> <jh80.chung at samsung.com>; Tom Rini <trini at konsulko.com>
> Cc: u-boot at lists.denx.de
> Subject: Re: [PATCH 1/2] mmc: Imply HS200 cap with mmc-hs400 prop to match linux
> 
> 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 :)

I want to follow the linux kernel. 

> 
> Reviewed-by: Quentin Schulz <quentin.schulz at theobrma-systems.com>

Reviewed-by: Jaehoon Chung <jh80.chung at samsung.com>

Best Regards,
Jaehoon Chung

> 
> Cheers,
> Quentin