Re: [PATCH 5/5] SDIO: put active devices into 1-bit mode during suspend

David Vrabel
2010-02-10T16:03:37Z

Chris Ball wrote:
> Hi David,
>
> > Why? Is this for a specific card that doesn't support
> > asynchronous card interrupts while in 4-bit mode? If so, I'd
> > suggest a card quirk for this and only switch modes for these
> > cards.
>
> (As a check that we're on the same page -- sdio_disable_wide() is only
> called if MMC_PM_KEEP_POWER is true, which means the system is going
> to be suspended but the card will remain externally powered without
> its clock.)
>
> Under the circumstances above, it's a requirement of the SDIO spec
> that moving to 1-bit mode must happen before stopping the clock if
> the interrupt mechanism is to be used to wake the host, and the
> chipset we've been using (Via VX855) fails to generate a wakeup if
> the switch isn't made. Do you have experience of another chipset
> that doesn't need the switch to 1-bit mode for a clockless wakeup?

I couldn't find anything in the SDIO specification (you know the section
number?). Part A2 has a requirement that the controller be placed into
1-bit mode but this doesn't mean that the card has to be.

Maybe it's not really a big deal, a single command only costs a few 10s
of microseconds anyway.

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