Re: [PATCH V4 1/4] mmc: core: Initial support for MMC power sequences

[NeilBrown <neilb@suse.de>]

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On Mon, 2 Feb 2015 16:10:29 +0100 Ulf Hansson <ulf.hansson@linaro.org> wrote:

> On 2 February 2015 at 16:05, Russell King - ARM Linux
> <linux@arm.linux.org.uk> wrote:
> > On Mon, Feb 02, 2015 at 03:57:37PM +0100, Ulf Hansson wrote:
> >> On 30 January 2015 at 23:27, NeilBrown <neilb@suse.de> wrote:
> >> > Shortly before this call is
> >> >
> >> >         host->ios.power_mode = MMC_POWER_ON;
> >> >         mmc_set_ios(host);
> >> >
> >> > and omap_hsmmc_set_ios() contains:
> >> >
> >> >                 switch (ios->power_mode) {
> >> >                 ....
> >> >                 case MMC_POWER_ON:
> >> >                         do_send_init_stream = 1;
> >> >                         break;
> >> >
> >> >
> >> >         if (do_send_init_stream)
> >> >                 send_init_stream(host);
> >> >
> >> > Which sends the "init stream" to the card.
> >> > If the card is still being reset at this time, the stream may not
> >> > be effective.
> >> >
> >> > I find that about 10%-20% of the time when I release the reset line
> >> > *after* the sequence is sent, my card fails to initialised.  When I
> >> > release *before* the sequence is sent, it never fails.
> >>
> >> Okay, thanks for providing these details.
> >
> > The right thing to do then is to pulse the reset line at the pre-power-up
> > stage.
> 
> I don't think that will work, since the card hasn't yet been powered
> and will thus not respond properly to the reset.

My understanding, at least in the case of my hardware, is that the power-on
is sufficient to reset the device.
In my case, the one supply is shared between two devices (wifi and bluetooth)
so if the bluetooth is on, then the wifi cannot be power-cycled.  That is
when the reset is particularly needed.

I'll try to arrange some testing to confirm this is the case.  Of course,
this would not be general result, it would only be relevant for my hardware.

NeilBrown

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