Re: [PATCH] mmc: dw_mmc: Add support for multiple SD cards on one host interface

[Ulf Hansson <ulf.hansson@linaro.org>]

On 30 September 2017 at 17:39, Bernd Edlinger <bernd.edlinger@hotmail.de> wrote:
>
> Needs external logic to multiplex the clock signal,
> which is controlled by a GPIO output pin.
>
> Only the selected SD card receives the clock,
> while the other SD card's clock is forced to LOW.
> DATA and CMD lines can be connected to both SD cards.
>
> On warm-start UBOOT should use a sequence of
> CMD12 and CMD7 with RCA=0 to force any active SD card
> to stop transmission and release the DATA bus.

I doubt that is sufficient to support multiple slots.

Sometimes the mmc core needs to perform a sequence of operations
towards *one* host/card and that must be done in guaranteed manner, to
that no other operations are performed for another card/host
in-between.

Perhaps if you are lucky you may get something that is very fragile to
work, but in the end I think the core needs to play along. Moreover,
dw_mmc has recently removed its multiple slot support - simply because
the complexity wasn't worth it.

Unless Jaehoon have changed his mind, I am not going to pick this up.

[...]

Kind regards
Uffe