linux-kernel - Re: [PATCH 3/4] mmc: sdio: support switching to 1-bit before turning off clocks

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Date:	Wed, 4 Mar 2015 16:28:48 +1100
From:	NeilBrown <neilb@...e.de>
To:	Tony Lindgren <tony@...mide.com>
Cc:	Ulf Hansson <ulf.hansson@...aro.org>,
	Andreas Fenkart <afenkart@...il.com>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	GTA04 owners <gta04-owner@...delico.com>,
	NeilBrown <neil@...wn.name>,
	linux-omap <linux-omap@...r.kernel.org>,
	Florian Vaussard <florian.vaussard@...l.ch>,
	Ash Charles <ash@...stix.com>
Subject: Re: [PATCH 3/4] mmc: sdio: support switching to 1-bit before
 turning off clocks

On Tue, 3 Mar 2015 14:53:55 -0800 Tony Lindgren <tony@...mide.com> wrote:

> * NeilBrown <neilb@...e.de> [150223 18:47]:
> > According to section 7.1.2 of
> > 
> > http://www.sandisk.com/media/File/OEM/Manuals/SD_SDIO_specsv1.pdf
> > 
> >     In the case where the interrupt mechanism is used to wake the host while
> >     the card is in a low power state (i.e. no clocks), Both the card and the
> >     host shall be placed into the 1-bit SD mode prior to stopping the clock.
> > 
> > This is particularly important for the Marvell "libertas" wifi chip
> > in the GTA04.  While in 4-bit mode it will only signal an interrupt
> > when the clock is running (which is why setting CLKEXTFREE is
> > important).
> > In 1-bit mode, the interrupt is asynchronous (explained in OMAP3
> > TRM description of the CIRQ flag to MMCHS_STAT:
> > 
> >   In 1-bit mode, interrupt source is asynchronous (can be a source of
> >   asynchronous wakeup).
> >   In 4-bit mode, interrupt source is sampled during the interrupt
> >   cycle.
> > 
> > )
> > 
> > It is awkward to simply set 1-bit mode in ->runtime_suspend
> > as that will call mmc_set_ios which calls ops->set_ios(),
> > which will likely call pm_runtime_get_sync(), on the device that
> > is currently suspending.  This deadlocks.
> > 
> > So:
> >  - create a work_struct to schedule setting of 1-bit mode
> >  - introduce an 'sdio_narrowed' state flag which transitions:
> >      0 (normal) -> 1 (convert to 1-bit pending) ->
> >          2 (have switch to 1-bit mode) -> 0 (normal)
> >  - create a function mmc_sdio_want_no_clocks() which can be called
> >    when the driver wants to turn off clocks (presumably after an
> >    idle timeout).  This either succeeds (in 1-bit mode) or fails
> >    and schedules the work to switch to 1-bit mode.
> >  - when the host is claimed, if sdio_narrowed is 2, restore the
> >    4-bit bus
> >  - When the host is released, if sdio_narrowed is 1, then some
> >    caller other  than our worker claimed the host first, so
> >    clear sdio_narrowed.
> > 
> > This all allows a graceful and race-free switch to 1-bit mode
> > before switching off the clocks, if SDIO interrupts are enabled.
> > 
> > A host should call mmc_sdio_want_no_clocks() when about to turn off
> > clocks if sdio interrupts are enabled, and the ->disable() function
> > should not use a timeout (pm_runtime_put_autosuspend) if
> > ->sdio_narrowed is 2.
> 
> Wow! A mystery finally solved for why libertas_sdio using devices
> like overo won't work for the wakeirqs.. The interface has to be
> in 1-bit mode for libertas to produce any SDIO interrupts..
> 
> Below is a patch enabling some more SDIO wakeirqs. Seems to work
> on overo now too :) So tor the whole series, please feel free to
> add:
> 
> Tested-by: Tony Lindgren <tony@...mide.com>

Thanks a lot!


> 
> 8< -------------------
> From: Tony Lindgren <tony@...mide.com>
> Date: Thu, 26 Feb 2015 16:16:03 -0800
> Subject: [PATCH] ARM: dts: Fix omap3 SDIO wakeirqs for devices using sdio_libertas
> 
> Turns out the the MMC interface needs to be in 1-bit mode for the
> libertas card to send any SDIO interrupts as pointed out by
> NeilBrown <neilb@...e.de>. Now that the MMC framework is getting
> fixed for setting 1-bit mode for idle, we can enable SDIO wakeirqs
> for libertas using devices too.
> 
> Cc: Andreas Fenkart <afenkart@...il.com>
> Cc: Ash Charles <ash@...stix.com>
> Cc: Florian Vaussard <florian.vaussard@...l.ch>
> Cc: NeilBrown <neil@...wn.name>
> Signed-off-by: Tony Lindgren <tony@...mide.com>
> 
> --- a/arch/arm/boot/dts/omap3-gta04.dtsi
> +++ b/arch/arm/boot/dts/omap3-gta04.dtsi
> @@ -367,6 +367,7 @@
>  };
>  
>  &mmc2 {
> +	interrupts-extended = <&intc 86 &omap3_pmx_core 0x12e>;
>  	vmmc-supply = <&vaux4>;
>  	bus-width = <4>;
>  	ti,non-removable;

I had 

+       interrupts-extended = <&intc 86 &gpio5 5 0>; /* GPIO_133 */
+       pinctrl-names = "default", "idle";
+       pinctrl-0 = <&mmc2_pins>;
+       pinctrl-1 = <&mmc2_cirq_pin>;

together with

+       mmc2_cirq_pin: pinmux_cirq_pin {
+               pinctrl-single,pins = <
+                       OMAP3_CORE1_IOPAD(0x215e, PIN_INPUT_PULLUP | MUX_MODE4) 
+               >;
+       };
+


and a longer definition for mmc2_pins.

Is that one line reconfigure the pin on demand?  How does that work?


Thanks,
NeilBrown

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