Re: MMC: Make the configuration memory resource optional

Ian Molton
2009-08-05T22:34:53Z

Guennadi Liakhovetski wrote:

> How do we verify this? Do I need some "very fast" card, so that sd would
> try to drive the clock beyond pdata->hclk / 2, which should then fail?

One way would be a 'scope on the card pins, but since you havent said I
am assuming you have not altered the clock-speed setting routine.

Here you can see why I didnt like the silently-drop-conf-accesses
version of the patch. If you had not made conf area accesses silently
succeed, you'd have found one lurking in the set_clock function.

Since your controller has no CNF area, it was discarding the write to
the 1:1 clock bit (that isnt in its none-existant conf area) and thus
you got the next lowest clock as a result (/2)

> Currently I'm using 24MHz (copied from the original driver), and the only
> thing I know about the controller is its "Maximum operating frequency: 25
> MHz."

Thats the HCLK frequency, not the card clock.

the TMIO MFD devices can divide this HCLK by anything from 512 to 2, and
MFD devices have a facility to disable the divider, yielding full HCLK
speed as the card clock.

If you havent already found a 1:1 clock enable bit on your device, you
might try looking for it - it'd yield a near linear factor-of-two speed
increase.

-Ian