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

Tony Lindgren
2015-03-03T23:09:27Z

* NeilBrown <neilb@suse.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@atomide.com>

8< -------------------
From: Tony Lindgren <tony@atomide.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@suse.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@gmail.com>
Cc: Ash Charles <ash@gumstix.com>
Cc: Florian Vaussard <florian.vaussard@epfl.ch>
Cc: NeilBrown <neil@brown.name>
Signed-off-by: Tony Lindgren <tony@atomide.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;
--- a/arch/arm/boot/dts/omap3-overo-base.dtsi
+++ b/arch/arm/boot/dts/omap3-overo-base.dtsi
@@ -185,6 +185,7 @@
&mmc2 {
pinctrl-names = "default";
pinctrl-0 = <&mmc2_pins>;
+ interrupts-extended = <&intc 86 &omap3_pmx_core 0x12e>;
vmmc-supply = <&w3cbw003c_npoweron>;
vqmmc-supply = <&w3cbw003c_bt_nreset>;
vmmc_aux-supply = <&w3cbw003c_wifi_nreset>;