[PATCH 0/2] mmc: core: Fix Marvell WiFi reset by adding SDIO API to replug card

[PATCH 0/2] mmc: core: Fix Marvell WiFi reset by adding SDIO API to replug card

[Douglas Anderson]

As talked about in the thread at:

http://lkml.kernel.org/r/CAD=FV=X7P2F1k_zwHc0mbtfk55-rucTz_GoDH=PL6zWqKYcpuw@mail.gmail.com

...when the Marvell WiFi card tries to reset itself it kills
Bluetooth.  It was observed that we could re-init the card properly by
unbinding / rebinding the host controller.  It was also observed that
in the downstream Chrome OS codebase the solution used was
mmc_remove_host() / mmc_add_host(), which is similar to the solution
in this series.

So far I've only done testing of this series using the reset test
source that can be simulated via sysfs.  Specifically I ran this test:

for i in $(seq 1000); do
  echo "LOOP $i --------"
  echo 1 > /sys/kernel/debug/mwifiex/mlan0/reset

  while true; do
    if ! ping -w15 -c1 "${GW}" >/dev/null 2>&1; then
      fail=$(( fail + 1 ))
      echo "Fail WiFi ${fail}"
      if [[ ${fail} == 3 ]]; then
        exit 1
      fi
    else
      fail=0
      break
    fi
  done

  hciconfig hci0 down
  sleep 1
  if ! hciconfig hci0 up; then
    echo "Fail BT"
    exit 1
  fi
done

I ran this several times and got several hundred iterations each
before a failure.  When I saw failures:

* Once I saw a "Fail BT"; manually resetting the card again fixed it.
  I didn't give it time to see if it would have detected this
  automatically.
* Once I saw the ping fail because (for some reason) my device only
  got an IPv6 address from my router and the IPv4 ping failed.  I
  changed my script to use 'ping6' to see if that would help.
* Once I saw the ping fail because the higher level network stack
  ("shill" in my case) seemed to crash.  A few minutes later the
  system recovered itself automatically.  https://crbug.com/984593 if
  you want more details.
* Sometimes while I was testing I saw "Fail WiFi 1" indicating a
  transitory failure.  Usually this was an association failure, but in
  one case I saw the device do "Firmware wakeup failed" after I
  triggered the reset.  This caused the driver to trigger a re-reset
  of itself which eventually recovered things.  This was good because
  it was an actual test of the normal reset flow (not the one
  triggered via sysfs).


Douglas Anderson (2):
  mmc: core: Add sdio_trigger_replug() API
  mwifiex: Make use of the new sdio_trigger_replug() API to reset

 drivers/mmc/core/core.c                     | 28 +++++++++++++++++++--
 drivers/mmc/core/sdio_io.c                  | 20 +++++++++++++++
 drivers/net/wireless/marvell/mwifiex/sdio.c | 14 +++--------
 include/linux/mmc/host.h                    | 15 ++++++++++-
 include/linux/mmc/sdio_func.h               |  2 ++
 5 files changed, 65 insertions(+), 14 deletions(-)

-- 
2.22.0.510.g264f2c817a-goog

[PATCH 1/2] mmc: core: Add sdio_trigger_replug() API

[Douglas Anderson]

When using Marvell WiFi SDIO cards, it is not uncommon for Linux WiFi
driver to fully lose the communication channel to the firmware running
on the card.  Presumably the firmware on the card has a bug or two in
it and occasionally crashes.

The Marvell WiFi driver attempts to recover from this problem.
Specifically the driver has the function mwifiex_sdio_card_reset()
which is called when communcation problems are found.  That function
attempts to reset the state of things by utilizing the mmc_hw_reset()
function.

The current solution is a bit complex because the Marvell WiFi driver
needs to manually deinit and reinit the WiFi driver around the reset
call.  This means it's going through a bunch of code paths that aren't
normally tested.  However, complexity isn't our only problem.  The
other (bigger) problem is that Marvell WiFi cards are often combo
WiFi/Bluetooth cards and Bluetooth runs on a second SDIO func.  While
the WiFi driver knows that it should re-init its own state around the
mmc_hw_reset() call there is no good way to inform the Bluetooth
driver.  That means that in Linux today when you reset the Marvell
WiFi driver you lose all Bluetooth communication.  Doh!

One way to fix the above problems is to leverage a more standard way
to reset the Marvell WiFi card where we go through the same code paths
as card unplug and the card plug.  In this patch we introduce a new
API call for doing just that: sdio_trigger_replug().  This API call
will trigger an unplug of the SDIO card followed by a plug of the
card.  As part of this the card will be nicely reset.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

 drivers/mmc/core/core.c       | 28 ++++++++++++++++++++++++++--
 drivers/mmc/core/sdio_io.c    | 20 ++++++++++++++++++++
 include/linux/mmc/host.h      | 15 ++++++++++++++-
 include/linux/mmc/sdio_func.h |  2 ++
 4 files changed, 62 insertions(+), 3 deletions(-)

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 9020cb2490f7..48a7d23aed26 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -2164,6 +2164,12 @@ int mmc_sw_reset(struct mmc_host *host)
 }
 EXPORT_SYMBOL(mmc_sw_reset);
 
+void mmc_trigger_replug(struct mmc_host *host)
+{
+	host->trigger_replug_state = MMC_REPLUG_STATE_UNPLUG;
+	_mmc_detect_change(host, 0, false);
+}
+
 static int mmc_rescan_try_freq(struct mmc_host *host, unsigned freq)
 {
 	host->f_init = freq;
@@ -2217,6 +2223,11 @@ int _mmc_detect_card_removed(struct mmc_host *host)
 	if (!host->card || mmc_card_removed(host->card))
 		return 1;
 
+	if (host->trigger_replug_state == MMC_REPLUG_STATE_UNPLUG) {
+		mmc_card_set_removed(host->card);
+		return 1;
+	}
+
 	ret = host->bus_ops->alive(host);
 
 	/*
@@ -2329,8 +2340,21 @@ void mmc_rescan(struct work_struct *work)
 	mmc_bus_put(host);
 
 	mmc_claim_host(host);
-	if (mmc_card_is_removable(host) && host->ops->get_cd &&
-			host->ops->get_cd(host) == 0) {
+
+	/*
+	 * Move through the state machine if we're triggering an unplug
+	 * followed by a re-plug.
+	 */
+	if (host->trigger_replug_state == MMC_REPLUG_STATE_UNPLUG) {
+		host->trigger_replug_state = MMC_REPLUG_STATE_PLUG;
+		_mmc_detect_change(host, 0, false);
+	} else if (host->trigger_replug_state == MMC_REPLUG_STATE_PLUG) {
+		host->trigger_replug_state = MMC_REPLUG_STATE_NONE;
+	}
+
+	if (host->trigger_replug_state == MMC_REPLUG_STATE_PLUG ||
+	    (mmc_card_is_removable(host) && host->ops->get_cd &&
+			host->ops->get_cd(host) == 0)) {
 		mmc_power_off(host);
 		mmc_release_host(host);
 		goto out;
diff --git a/drivers/mmc/core/sdio_io.c b/drivers/mmc/core/sdio_io.c
index 2ba00acf64e6..1c5c2a3ebe5e 100644
--- a/drivers/mmc/core/sdio_io.c
+++ b/drivers/mmc/core/sdio_io.c
@@ -811,3 +811,23 @@ void sdio_retune_release(struct sdio_func *func)
 	mmc_retune_release(func->card->host);
 }
 EXPORT_SYMBOL_GPL(sdio_retune_release);
+
+/**
+ *	sdio_trigger_replug - trigger an "unplug" + "plug" of the card
+ *	@func: SDIO function attached to host
+ *
+ *	When you call this function we will schedule events that will
+ *	make it look like the card contining the given SDIO func was
+ *	unplugged and then re-plugged-in.  This is as close as possible
+ *	to a full reset of the card that can be achieved.
+ *
+ *	NOTE: routnine will temporarily make the card look as if it is
+ *	removable even if it is marked non-removable.
+ *
+ *	This function should be called while the host is claimed.
+ */
+void sdio_trigger_replug(struct sdio_func *func)
+{
+	mmc_trigger_replug(func->card->host);
+}
+EXPORT_SYMBOL(sdio_trigger_replug);
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index a9b12322c775..e0d41a1bcf17 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -410,6 +410,12 @@ struct mmc_host {
 
 	bool			trigger_card_event; /* card_event necessary */
 
+	/* state machine for triggering unplug/replug */
+#define MMC_REPLUG_STATE_NONE	0		/* not doing unplug/replug */
+#define MMC_REPLUG_STATE_UNPLUG	1		/* do unplug next */
+#define MMC_REPLUG_STATE_PLUG	2		/* do plug next */
+	u8			trigger_replug_state;
+
 	struct mmc_card		*card;		/* device attached to this host */
 
 	wait_queue_head_t	wq;
@@ -530,7 +536,12 @@ int mmc_regulator_get_supply(struct mmc_host *mmc);
 
 static inline int mmc_card_is_removable(struct mmc_host *host)
 {
-	return !(host->caps & MMC_CAP_NONREMOVABLE);
+	/*
+	 * A non-removable card briefly looks removable if code has forced
+	 * a re-plug of the card.
+	 */
+	return host->trigger_replug_state != MMC_REPLUG_STATE_NONE ||
+		!(host->caps & MMC_CAP_NONREMOVABLE);
 }
 
 static inline int mmc_card_keep_power(struct mmc_host *host)
@@ -583,4 +594,6 @@ static inline enum dma_data_direction mmc_get_dma_dir(struct mmc_data *data)
 int mmc_send_tuning(struct mmc_host *host, u32 opcode, int *cmd_error);
 int mmc_abort_tuning(struct mmc_host *host, u32 opcode);
 
+void mmc_trigger_replug(struct mmc_host *host);
+
 #endif /* LINUX_MMC_HOST_H */
diff --git a/include/linux/mmc/sdio_func.h b/include/linux/mmc/sdio_func.h
index 5a177f7a83c3..0d6c73768ae3 100644
--- a/include/linux/mmc/sdio_func.h
+++ b/include/linux/mmc/sdio_func.h
@@ -173,4 +173,6 @@ extern void sdio_retune_crc_enable(struct sdio_func *func);
 extern void sdio_retune_hold_now(struct sdio_func *func);
 extern void sdio_retune_release(struct sdio_func *func);
 
+extern void sdio_trigger_replug(struct sdio_func *func);
+
 #endif /* LINUX_MMC_SDIO_FUNC_H */
-- 
2.22.0.510.g264f2c817a-goog

[PATCH 2/2] mwifiex: Make use of the new sdio_trigger_replug() API to reset

[Douglas Anderson]

As described in the patch ("mmc: core: Add sdio_trigger_replug()
API"), the current mwifiex_sdio_card_reset() is broken in the cases
where we're running Bluetooth on a second SDIO func on the same card
as WiFi.  The problem goes away if we just use the
sdio_trigger_replug() API call.

NOTE: Even though with this new solution there is less of a reason to
do our work from a workqueue (the unplug / plug mechanism we're using
is possible for a human to perform at any time so the stack is
supposed to handle it without it needing to be called from a special
context), we still need a workqueue because the Marvell reset function
could called from a context where sleeping is invalid and thus we
can't claim the host.  One example is Marvell's wakeup_timer_fn().

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

 drivers/net/wireless/marvell/mwifiex/sdio.c | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

diff --git a/drivers/net/wireless/marvell/mwifiex/sdio.c b/drivers/net/wireless/marvell/mwifiex/sdio.c
index 24c041dad9f6..f77ad2615f08 100644
--- a/drivers/net/wireless/marvell/mwifiex/sdio.c
+++ b/drivers/net/wireless/marvell/mwifiex/sdio.c
@@ -2218,14 +2218,6 @@ static void mwifiex_sdio_card_reset_work(struct mwifiex_adapter *adapter)
 {
 	struct sdio_mmc_card *card = adapter->card;
 	struct sdio_func *func = card->func;
-	int ret;
-
-	mwifiex_shutdown_sw(adapter);
-
-	/* power cycle the adapter */
-	sdio_claim_host(func);
-	mmc_hw_reset(func->card->host);
-	sdio_release_host(func);
 
 	/* Previous save_adapter won't be valid after this. We will cancel
 	 * pending work requests.
@@ -2233,9 +2225,9 @@ static void mwifiex_sdio_card_reset_work(struct mwifiex_adapter *adapter)
 	clear_bit(MWIFIEX_IFACE_WORK_DEVICE_DUMP, &card->work_flags);
 	clear_bit(MWIFIEX_IFACE_WORK_CARD_RESET, &card->work_flags);
 
-	ret = mwifiex_reinit_sw(adapter);
-	if (ret)
-		dev_err(&func->dev, "reinit failed: %d\n", ret);
+	sdio_claim_host(func);
+	sdio_trigger_replug(func);
+	sdio_release_host(func);
 }
 
 /* This function read/write firmware */
-- 
2.22.0.510.g264f2c817a-goog

Re: [PATCH 2/2] mwifiex: Make use of the new sdio_trigger_replug() API to reset

[Brian Norris]

Hi Doug,

On Tue, Jul 16, 2019 at 09:42:09AM -0700, Doug Anderson wrote:
> As described in the patch ("mmc: core: Add sdio_trigger_replug()
> API"), the current mwifiex_sdio_card_reset() is broken in the cases
> where we're running Bluetooth on a second SDIO func on the same card
> as WiFi.  The problem goes away if we just use the
> sdio_trigger_replug() API call.

I'm unfortunately not a good evaluator of SDIO/MMC stuff, so I'll mostly
leave that to others and assume that the "replug" description is pretty
much all I need to know.

> NOTE: Even though with this new solution there is less of a reason to
> do our work from a workqueue (the unplug / plug mechanism we're using
> is possible for a human to perform at any time so the stack is
> supposed to handle it without it needing to be called from a special
> context), we still need a workqueue because the Marvell reset function
> could called from a context where sleeping is invalid and thus we
> can't claim the host.  One example is Marvell's wakeup_timer_fn().
> 
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
> 
>  drivers/net/wireless/marvell/mwifiex/sdio.c | 14 +++-----------
>  1 file changed, 3 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/net/wireless/marvell/mwifiex/sdio.c b/drivers/net/wireless/marvell/mwifiex/sdio.c
> index 24c041dad9f6..f77ad2615f08 100644
> --- a/drivers/net/wireless/marvell/mwifiex/sdio.c
> +++ b/drivers/net/wireless/marvell/mwifiex/sdio.c
> @@ -2218,14 +2218,6 @@ static void mwifiex_sdio_card_reset_work(struct mwifiex_adapter *adapter)
>  {
>  	struct sdio_mmc_card *card = adapter->card;
>  	struct sdio_func *func = card->func;
> -	int ret;
> -
> -	mwifiex_shutdown_sw(adapter);

I'm very mildly unhappy to see this driver diverge from the PCIe one
again, but the only way it makes sense to do things the same is if there
is such thing as a "function level reset" for SDIO (i.e., doesn't also
kill the Bluetooth function). But it appears we don't really have such a
thing.

> -
> -	/* power cycle the adapter */
> -	sdio_claim_host(func);
> -	mmc_hw_reset(func->card->host);
> -	sdio_release_host(func);
>  
>  	/* Previous save_adapter won't be valid after this. We will cancel

^^^ FTR, the "save_adapter" note was already obsolete as of

  cc75c577806a mwifiex: get rid of global save_adapter and sdio_work

but the clear_bit() calls were (before this patch) still useful for
other reasons.

>  	 * pending work requests.
> @@ -2233,9 +2225,9 @@ static void mwifiex_sdio_card_reset_work(struct mwifiex_adapter *adapter)
>  	clear_bit(MWIFIEX_IFACE_WORK_DEVICE_DUMP, &card->work_flags);
>  	clear_bit(MWIFIEX_IFACE_WORK_CARD_RESET, &card->work_flags);

But now, I don't think you need these clear_bit() calls any more --
you're totally destroying the card and its workqueue on remove(). (And
anyway, MWIFIEX_IFACE_WORK_CARD_RESET was just cleared by your caller.)

>  
> -	ret = mwifiex_reinit_sw(adapter);
> -	if (ret)
> -		dev_err(&func->dev, "reinit failed: %d\n", ret);
> +	sdio_claim_host(func);
> +	sdio_trigger_replug(func);
> +	sdio_release_host(func);

And...we're approximately back to where we were 4 years ago :)

commit b4336a282db86b298b70563f8ed51782b36b772c
Author: Andreas Fenkart <afenkart@gmail.com>
Date:   Thu Jul 16 18:50:01 2015 +0200

    mwifiex: sdio: reset adapter using mmc_hw_reset

Anyway, assuming the "function reset" thing isn't workable, and you drop
the clear_bit() stuff, I think this is fine:

Reviewed-by: Brian Norris <briannorris@chromium.org>

>  }
>  
>  /* This function read/write firmware */
> -- 
> 2.22.0.510.g264f2c817a-goog
> 

Re: [PATCH 1/2] mmc: core: Add sdio_trigger_replug() API

[Matthias Kaehlcke]

On Tue, Jul 16, 2019 at 09:42:08AM -0700, Douglas Anderson wrote:
> When using Marvell WiFi SDIO cards, it is not uncommon for Linux WiFi
> driver to fully lose the communication channel to the firmware running
> on the card.  Presumably the firmware on the card has a bug or two in
> it and occasionally crashes.
> 
> The Marvell WiFi driver attempts to recover from this problem.
> Specifically the driver has the function mwifiex_sdio_card_reset()
> which is called when communcation problems are found.  That function
> attempts to reset the state of things by utilizing the mmc_hw_reset()
> function.
> 
> The current solution is a bit complex because the Marvell WiFi driver
> needs to manually deinit and reinit the WiFi driver around the reset
> call.  This means it's going through a bunch of code paths that aren't
> normally tested.  However, complexity isn't our only problem.  The
> other (bigger) problem is that Marvell WiFi cards are often combo
> WiFi/Bluetooth cards and Bluetooth runs on a second SDIO func.  While
> the WiFi driver knows that it should re-init its own state around the
> mmc_hw_reset() call there is no good way to inform the Bluetooth
> driver.  That means that in Linux today when you reset the Marvell
> WiFi driver you lose all Bluetooth communication.  Doh!
> 
> One way to fix the above problems is to leverage a more standard way
> to reset the Marvell WiFi card where we go through the same code paths
> as card unplug and the card plug.  In this patch we introduce a new
> API call for doing just that: sdio_trigger_replug().  This API call
> will trigger an unplug of the SDIO card followed by a plug of the
> card.  As part of this the card will be nicely reset.
> 
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
> 
>  drivers/mmc/core/core.c       | 28 ++++++++++++++++++++++++++--
>  drivers/mmc/core/sdio_io.c    | 20 ++++++++++++++++++++
>  include/linux/mmc/host.h      | 15 ++++++++++++++-
>  include/linux/mmc/sdio_func.h |  2 ++
>  4 files changed, 62 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index 9020cb2490f7..48a7d23aed26 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -2164,6 +2164,12 @@ int mmc_sw_reset(struct mmc_host *host)
>  }
>  EXPORT_SYMBOL(mmc_sw_reset);
>  
> +void mmc_trigger_replug(struct mmc_host *host)
> +{
> +	host->trigger_replug_state = MMC_REPLUG_STATE_UNPLUG;
> +	_mmc_detect_change(host, 0, false);
> +}
> +
>  static int mmc_rescan_try_freq(struct mmc_host *host, unsigned freq)
>  {
>  	host->f_init = freq;
> @@ -2217,6 +2223,11 @@ int _mmc_detect_card_removed(struct mmc_host *host)
>  	if (!host->card || mmc_card_removed(host->card))
>  		return 1;
>  
> +	if (host->trigger_replug_state == MMC_REPLUG_STATE_UNPLUG) {
> +		mmc_card_set_removed(host->card);
> +		return 1;
> +	}
> +
>  	ret = host->bus_ops->alive(host);
>  
>  	/*
> @@ -2329,8 +2340,21 @@ void mmc_rescan(struct work_struct *work)
>  	mmc_bus_put(host);
>  
>  	mmc_claim_host(host);
> -	if (mmc_card_is_removable(host) && host->ops->get_cd &&
> -			host->ops->get_cd(host) == 0) {
> +
> +	/*
> +	 * Move through the state machine if we're triggering an unplug
> +	 * followed by a re-plug.
> +	 */
> +	if (host->trigger_replug_state == MMC_REPLUG_STATE_UNPLUG) {
> +		host->trigger_replug_state = MMC_REPLUG_STATE_PLUG;
> +		_mmc_detect_change(host, 0, false);
> +	} else if (host->trigger_replug_state == MMC_REPLUG_STATE_PLUG) {
> +		host->trigger_replug_state = MMC_REPLUG_STATE_NONE;
> +	}
> +
> +	if (host->trigger_replug_state == MMC_REPLUG_STATE_PLUG ||
> +	    (mmc_card_is_removable(host) && host->ops->get_cd &&
> +			host->ops->get_cd(host) == 0)) {

at first I was concerned there could be race conditions with the
different invocations of mmc_rescan(), but IIUC all calls are through
the host->detect work, so only one instance should be running at any
time.

>  		mmc_power_off(host);
>  		mmc_release_host(host);
>  		goto out;
> diff --git a/drivers/mmc/core/sdio_io.c b/drivers/mmc/core/sdio_io.c
> index 2ba00acf64e6..1c5c2a3ebe5e 100644
> --- a/drivers/mmc/core/sdio_io.c
> +++ b/drivers/mmc/core/sdio_io.c
> @@ -811,3 +811,23 @@ void sdio_retune_release(struct sdio_func *func)
>  	mmc_retune_release(func->card->host);
>  }
>  EXPORT_SYMBOL_GPL(sdio_retune_release);
> +
> +/**
> + *	sdio_trigger_replug - trigger an "unplug" + "plug" of the card
> + *	@func: SDIO function attached to host
> + *
> + *	When you call this function we will schedule events that will
> + *	make it look like the card contining the given SDIO func was

nit: containing

> + *	unplugged and then re-plugged-in.  This is as close as possible
> + *	to a full reset of the card that can be achieved.
> + *
> + *	NOTE: routnine will temporarily make the card look as if it is

nit: routine

Other than the typos this looks sane to me, I don't claim to have a
deep understanding of the MMC codebase though.

Reviewed-by: Matthias Kaehlcke <mka@chromium.org>

Re: [PATCH 1/2] mmc: core: Add sdio_trigger_replug() API

[Matthias Kaehlcke]

On Tue, Jul 16, 2019 at 09:42:08AM -0700, Douglas Anderson wrote:
> When using Marvell WiFi SDIO cards, it is not uncommon for Linux WiFi
> driver to fully lose the communication channel to the firmware running
> on the card.  Presumably the firmware on the card has a bug or two in
> it and occasionally crashes.
> 
> The Marvell WiFi driver attempts to recover from this problem.
> Specifically the driver has the function mwifiex_sdio_card_reset()
> which is called when communcation problems are found.  That function
> attempts to reset the state of things by utilizing the mmc_hw_reset()
> function.
> 
> The current solution is a bit complex because the Marvell WiFi driver
> needs to manually deinit and reinit the WiFi driver around the reset
> call.  This means it's going through a bunch of code paths that aren't
> normally tested.  However, complexity isn't our only problem.  The
> other (bigger) problem is that Marvell WiFi cards are often combo
> WiFi/Bluetooth cards and Bluetooth runs on a second SDIO func.  While
> the WiFi driver knows that it should re-init its own state around the
> mmc_hw_reset() call there is no good way to inform the Bluetooth
> driver.  That means that in Linux today when you reset the Marvell
> WiFi driver you lose all Bluetooth communication.  Doh!
> 
> One way to fix the above problems is to leverage a more standard way
> to reset the Marvell WiFi card where we go through the same code paths
> as card unplug and the card plug.  In this patch we introduce a new
> API call for doing just that: sdio_trigger_replug().  This API call
> will trigger an unplug of the SDIO card followed by a plug of the
> card.  As part of this the card will be nicely reset.
> 
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
> 
>  drivers/mmc/core/core.c       | 28 ++++++++++++++++++++++++++--
>  drivers/mmc/core/sdio_io.c    | 20 ++++++++++++++++++++
>  include/linux/mmc/host.h      | 15 ++++++++++++++-
>  include/linux/mmc/sdio_func.h |  2 ++
>  4 files changed, 62 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index 9020cb2490f7..48a7d23aed26 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -2164,6 +2164,12 @@ int mmc_sw_reset(struct mmc_host *host)
>  }
>  EXPORT_SYMBOL(mmc_sw_reset);
>  
> +void mmc_trigger_replug(struct mmc_host *host)
> +{
> +	host->trigger_replug_state = MMC_REPLUG_STATE_UNPLUG;
> +	_mmc_detect_change(host, 0, false);
> +}
> +
>  static int mmc_rescan_try_freq(struct mmc_host *host, unsigned freq)
>  {
>  	host->f_init = freq;
> @@ -2217,6 +2223,11 @@ int _mmc_detect_card_removed(struct mmc_host *host)
>  	if (!host->card || mmc_card_removed(host->card))
>  		return 1;
>  
> +	if (host->trigger_replug_state == MMC_REPLUG_STATE_UNPLUG) {
> +		mmc_card_set_removed(host->card);
> +		return 1;
> +	}
> +
>  	ret = host->bus_ops->alive(host);
>  
>  	/*
> @@ -2329,8 +2340,21 @@ void mmc_rescan(struct work_struct *work)
>  	mmc_bus_put(host);
>  
>  	mmc_claim_host(host);
> -	if (mmc_card_is_removable(host) && host->ops->get_cd &&
> -			host->ops->get_cd(host) == 0) {
> +
> +	/*
> +	 * Move through the state machine if we're triggering an unplug
> +	 * followed by a re-plug.
> +	 */
> +	if (host->trigger_replug_state == MMC_REPLUG_STATE_UNPLUG) {
> +		host->trigger_replug_state = MMC_REPLUG_STATE_PLUG;
> +		_mmc_detect_change(host, 0, false);
> +	} else if (host->trigger_replug_state == MMC_REPLUG_STATE_PLUG) {
> +		host->trigger_replug_state = MMC_REPLUG_STATE_NONE;
> +	}
> +
> +	if (host->trigger_replug_state == MMC_REPLUG_STATE_PLUG ||
> +	    (mmc_card_is_removable(host) && host->ops->get_cd &&
> +			host->ops->get_cd(host) == 0)) {

at first I was concerned there could be race conditions with the
different invocations of mmc_rescan(), but IIUC all calls are through
the host->detect work, so only one instance should be running at any
time.

>  		mmc_power_off(host);
>  		mmc_release_host(host);
>  		goto out;
> diff --git a/drivers/mmc/core/sdio_io.c b/drivers/mmc/core/sdio_io.c
> index 2ba00acf64e6..1c5c2a3ebe5e 100644
> --- a/drivers/mmc/core/sdio_io.c
> +++ b/drivers/mmc/core/sdio_io.c
> @@ -811,3 +811,23 @@ void sdio_retune_release(struct sdio_func *func)
>  	mmc_retune_release(func->card->host);
>  }
>  EXPORT_SYMBOL_GPL(sdio_retune_release);
> +
> +/**
> + *	sdio_trigger_replug - trigger an "unplug" + "plug" of the card
> + *	@func: SDIO function attached to host
> + *
> + *	When you call this function we will schedule events that will
> + *	make it look like the card contining the given SDIO func was

nit: containing

> + *	unplugged and then re-plugged-in.  This is as close as possible
> + *	to a full reset of the card that can be achieved.
> + *
> + *	NOTE: routnine will temporarily make the card look as if it is

nit: routine

Other than the typos this looks sane to me, I don't claim to have a
deep understanding of the MMC codebase though.

Reviewed-by: Matthias Kaehlcke <mka@chromium.org>