[PATCH v2 18/20] mmc: sdio: enable a default power off mode of the card

[Nicolas Pitre]

On Sun, 25 Jul 2010, Ohad Ben-Cohen wrote:

> On Thu, Jul 22, 2010 at 2:35 PM, Roger Quadros <roger.quadros at nokia.com> wrote:
> > On 07/21/2010 08:33 PM, ext Ohad Ben-Cohen wrote:
> >>
> >> Add support for an SDIO device to stay powered off even without
> >> the presence of an SDIO function driver. A host should explicitly
> >> ask for it by means of MMC_CAP_DONT_POWER_CARD, and the SDIO
> >> function driver should know it needs to call sdio_claim_power
> >> before accessing the device.
> >>
> >> Signed-off-by: Ohad Ben-Cohen<ohad at wizery.com>
> >
> > Shouldn't this be the default behaviour? If there is no function driver for
> > any of the functions of the card, then sdio core shold power off the card.
> >
> > I don't see a need for a special capability flag for this.
> >
> > in fact MMC_CAP_DONT_POWER_CARD does not seem like an mmc host's capability
> 
> Totally agree.
> 
> I didn't want to change the current behavior of the cards/funcs so I
> looked for a way to explicitly power down only specific cards.
> 
> Alternatively we could power down all cards at the end
> mmc_attach_sdio, and then power them up selectively in sdio_bus_probe,
> just before calling probe. If the probe succeeds, the function driver
> takes over. If the probe fails, we can power them down again.

Exactly!

> Is that what you meant ?
> 
> This would work both if the sdio function driver is already loaded, or
> will only be loaded at a later time. But I'm not too fond of the extra
> power on/off cycles that it will introduce for each card..

This is still way better than introducing knowledge about specific cards 
in the host drivers.


Nicolas