Re: New MMC maintainer needed

[David Vrabel <david.vrabel@csr.com>]

Philip Langdale wrote:
> 
> Both the (Simplified) SD and SDIO specifications do not formally
> define the 'low voltage' range in the way the MMC spec does. ie: You
> won't find anything in the SD specs that even tell you what the range
> is - it just says that it exists.

Standard SD/SDIO cards only support 2.7-3.6V.

1.8V operation is added in SD physical spec 3.00 and is part of any of
the UHS-1 modes (SDR12-SDR104 and DDR50).  It has a different timings
and requires a different (3.00 compliant) host controller.

> So we (I wrote the first incarnation of this check for normal SD
> cards) decided to bail if a card requested the low voltage range.
> Now, if there's actually hardware out there that is SD/SDIO and
> operates at 1.8V, we should probably do something more appropriate.
> :-)

The SD/SDIO stack must ignore reserved bits unless a per-card quirk
gives an additional meaning to the reserved bit.

> It's obviously an easy change but I'd feel a lot more comfortable if 
> someone can point us to a document that states that the SD/SDIO low 
> voltage range is defined to match the MMC one. Maybe one of the NDA 
> docs actually states this.

The non-simplified documents don't say anything on this.

David
-- 
David Vrabel, Senior Software Engineer, Drivers
CSR, Churchill House, Cambridge Business Park,  Tel: +44 (0)1223 692562
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