[PATCH 1/2] mmc: core: Improve marking broken HPI through devicetree

[Ulf Hansson]

[...]

> Well I think we still have a very small sample size, the sun4i, sun5i and
> sun7i boards (all using the same mmc controller afaik) have the broken-hpi
> set, the sun6i and sun8i seem to be working fine (different mmc
> controller?).
> I'm not so sure it is an eMMC specific problem though. The module we're
> using is a high-end micron part, industrial grade. Granted, it could be
> still broken there, but I find it less likely. Micron has an interessting
> technical document:
> "TN-52-05 e.EMMC Linux Enablement"
> talking specifically about HPI on eMMC.
> It also mentions HPI is a mmc/jedic 4.41 thing, afaik our controller is only
> 4.3 (which might not even matter according to Ulf if it is just a command).
>
> The datasheet of the chip I use, MTFC4GACAANA, also mentions explicitly that
> it supports HPI.
>
> Granted, it could still be broken, but I have doubts.

Perhaps the same eMMC is used without errors on other controllers?

>
>>
>> But given how rare eMMC-s are on sun4i/sun5i/sun7i I think the current
>> solution where we set a flag on the emmc dt node rather then on the
>> host node / in the host driver is fine.
>
> Yeah it is very limited, that is true, and I suppose I can live with that.
>>
>>
>> Taking your case into account too, that will bring us up to 2 cases
>> where we set the broken-hpi flag on the emmc node, which does not
>> really seem like a number to worry about.
>
> Actually, 4 :), there are 3 sun5i (tablets?) devices that suffer from this
> and my device now. The sun6i and sun8i devices are only 2 (the sinlinx
> devices in the current kernel) that a very quick grep (mmc-card ) showed.
> Grepping for non-removable yielded a bit more, like the chip sun5i-like
> device with a "non-removable" mmc, not sure what to make of that though.
>>
>>
>> TL;DR: Thanks for writing this patch set, but given recent developments
>> I believe that it is best to keep handling broken-hpi as we are doing
>> in current kernels and no changes are necessary.
>
> I would still recommend to add the capability and raise the flag for the
> sun[457]i devices though, as my gut thinks it's a problem with the sunxi IP
> there. But with the emmc-card level work around, it does solve/fix it, so
> what is the best way?

The best is clearly to make a proper debug investigation before we
decide to add a DT binding for the host.

I don't know on what level you are able to measure signals on the HW,
but if not, perhaps the newly TRACE support in the MMC core can help.

Kind regards
Uffe