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

[Stefan Roese <sr@denx.de>]

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.

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? 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?

Thanks,
Stefan