Re: SDIO "SD2" vs. SD-card "SD3" interface on BayTrail

[Adrian Hunter <adrian.hunter@intel.com>]

On 31/08/17 12:38, Stefan Roese wrote:
> Hi Andy, Hi Adrian,
> 
> On 04.07.2017 15:53, Andy Shevchenko wrote:
>> On Tue, 2017-07-04 at 14:53 +0200, Stefan Roese wrote:
>>> Hi,
>>>
>>> we are currently investigating, if its possible to connect a SDIO
>>> device (WLAN module) to the SD-card interface "SD3" of the BayTrail
>>> SoC instead of the SDIO interface "SD2". The BayTrail manual states,
>>> that the SDIO interface is capable of connecting SDIO devices. Is
>>> this also possible for the SD-card interface "SD3", even if its not
>>> explicitly mentioned in the manual? If not, why is this not possible?
>>>
>>> Any insight on this would be really helpful.
>>
>> Hmm... I have no documentation for SD/SDIO/eMMC for BayTrail except the
>> public one. Internally I found some charts that shows similarities
>> between two. So, taking that into consideration I would suggest to try
>> it out on real hardware (MinnowBoard MAX, for example), only impediment
>> I can see is the absence of support in the drivers in Linux OS. If you
>> need it only in U-Boot, you perhaps may fix it easily.
>>
>> P.S. Adrian on vacation.
> 
> I hope your vacation was great!
> 
> Sorry for getting back to this, but I would really like to get some
> more feedback on this. Perhaps Adrian has some additional comments
> about the SDIO usage of the SD interface (SD3 - PCI Device ID 0x0f16)
> on BayTrail.
> 
> I'm now running latest mainline Linux on this board and am trying to
> get the Linux MMC / SDIO subsystem to just detect a device on this
> SD PCI interface. For this I have added quite a bit of debug code to
> the MMC / SDIO code to see, if any device is detected on the SDIO
> port. But all command queries return timeout as far as I can tell.

I would usually interpret that to mean the SDIO card is not turned on.

> Adrian, do you have some additional information, if this mode of
> operation is possible at all on this SD-card interface, even if
> its not explicitly mentioned in the BayTrail datasheet?

I have used removable SDIO cards in SD slots before.  It should work.

>                                                         Or do you
> have some suggestions, how I could test such a basic SDIO connection
> (without integrating of the WLAN driver first) in the simplest way?

Only to try a removable SDIO card.