[PATCH v4] mmc: meson: Add driver for the SD/MMC host found on Amlogic MesonX SoCs

[Ulf Hansson]

On 4 February 2016 at 10:12, Carlo Caione <carlo at caione.org> wrote:
> On Wed, Feb 3, 2016 at 11:46 AM, Ulf Hansson <ulf.hansson at linaro.org> wrote:
>> On 2 February 2016 at 22:54, Carlo Caione <carlo at caione.org> wrote:
>
> [cut]
>
>> Huh, another broken MMC controller. :-)
>
> Oh, actually I found in the datasheet a couple of undocumented
> registers (also not used in the original Amlogic SDK code) that seems
> to have something to do with timeout (hard to say without proper
> documentation but they are called "Timeout counter for preload setting
> and present status" and "Timeout Counter Interrupt Enable for ARC/ARM"
> so I guess I'm on the right track here).
> I briefly tried yesterday to enable this timeout interrupt with a
> dummy value in the counter register (I have no idea how get this value
> from the clocking) and it seems working (the counter value is
> decremented when reading the register upon command completion).

Let's hope this works, as this will for sure be a better solution.

>
>> In some cases there are no data in the request, it's just a command
>> being sent. So to deal with this issue, you will have to adjust the
>> timer depending on the request we send to the controller.
>
> I see that the CMD13 used to poll the card has no data so in that case
> should we use a fixed / dummy value to use as timeout counter?
> I'm kind of confused here since the MMC drivers I'm looking at use the
> hardware timeout register only when the data->timeout_ns is actually
> present.

That's a different timeout value. It's elated to *each* block data
transfer and not the entire request. So it provides information to the
controller about what delays it shall accept during a block being
written/read.

More details is found in the electrical descriptions of the interface
in the eMMC/SD spec.

Kind regards
Uffe