mmc: core: prevent aggressive clock gating racing with ios updates

We have seen at least two different races when clock gating kicks in in a
middle of ios structure update.

First one happens when ios->clock is changed outside of aggressive clock
gating framework, for example via mmc_set_clock(). The race might happen
when we run following code:

mmc_set_ios():
	...
	if (ios->clock > 0)
		mmc_set_ungated(host);

Now if gating kicks in right after the condition check we end up setting
host->clk_gated to false even though we have just gated the clock. Next
time a request is started we try to ungate and restore the clock in
mmc_host_clk_hold(). However since we have host->clk_gated set to false the
original clock is not restored.

This eventually will cause the host controller to hang since its clock is
disabled while we are trying to issue a request. For example on Intel
Medfield platform we see:

[   13.818610] mmc2: Timeout waiting for hardware interrupt.
[   13.818698] sdhci: =========== REGISTER DUMP (mmc2)===========
[   13.818753] sdhci: Sys addr: 0x00000000 | Version:  0x00008901
[   13.818804] sdhci: Blk size: 0x00000000 | Blk cnt:  0x00000000
[   13.818853] sdhci: Argument: 0x00000000 | Trn mode: 0x00000000
[   13.818903] sdhci: Present:  0x1fff0000 | Host ctl: 0x00000001
[   13.818951] sdhci: Power:    0x0000000d | Blk gap:  0x00000000
[   13.819000] sdhci: Wake-up:  0x00000000 | Clock:    0x00000000
[   13.819049] sdhci: Timeout:  0x00000000 | Int stat: 0x00000000
[   13.819098] sdhci: Int enab: 0x00ff00c3 | Sig enab: 0x00ff00c3
[   13.819147] sdhci: AC12 err: 0x00000000 | Slot int: 0x00000000
[   13.819196] sdhci: Caps:     0x6bee32b2 | Caps_1:   0x00000000
[   13.819245] sdhci: Cmd:      0x00000000 | Max curr: 0x00000000
[   13.819292] sdhci: Host ctl2: 0x00000000
[   13.819331] sdhci: ADMA Err: 0x00000000 | ADMA Ptr: 0x00000000
[   13.819377] sdhci: ===========================================
[   13.919605] mmc2: Reset 0x2 never completed.

and it never recovers.

Second race might happen while running mmc_power_off():

static void mmc_power_off(struct mmc_host *host)
{
	host->ios.clock = 0;
	host->ios.vdd = 0;

[ clock gating kicks in here ]

	/*
	 * Reset ocr mask to be the highest possible voltage supported for
	 * this mmc host. This value will be used at next power up.
	 */
	host->ocr = 1 << (fls(host->ocr_avail) - 1);

	if (!mmc_host_is_spi(host)) {
		host->ios.bus_mode = MMC_BUSMODE_OPENDRAIN;
		host->ios.chip_select = MMC_CS_DONTCARE;
	}
	host->ios.power_mode = MMC_POWER_OFF;
	host->ios.bus_width = MMC_BUS_WIDTH_1;
	host->ios.timing = MMC_TIMING_LEGACY;
	mmc_set_ios(host);
}

If the clock gating worker kicks in while we are only partially updated the
ios structure the host controller gets incomplete ios and might not work as
supposed. Again on Intel Medfield platform we get:

[    4.185349] kernel BUG at drivers/mmc/host/sdhci.c:1155!
[    4.185422] invalid opcode: 0000 [#1] PREEMPT SMP
[    4.185509] Modules linked in:
[    4.185565]
[    4.185608] Pid: 4, comm: kworker/0:0 Not tainted 3.0.0+ #240 Intel Corporation Medfield/iCDKA
[    4.185742] EIP: 0060:[<c136364e>] EFLAGS: 00010083 CPU: 0
[    4.185827] EIP is at sdhci_set_power+0x3e/0xd0
[    4.185891] EAX: f5ff98e0 EBX: f5ff98e0 ECX: 00000000 EDX: 00000001
[    4.185970] ESI: f5ff977c EDI: f5ff9904 EBP: f644fe98 ESP: f644fe94
[    4.186049]  DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
[    4.186125] Process kworker/0:0 (pid: 4, ti=f644e000 task=f644c0e0 task.ti=f644e000)
[    4.186219] Stack:
[    4.186257]  f5ff98e0 f644feb0 c1365173 00000282 f5ff9460 f5ff96e0 f5ff96e0 f644feec
[    4.186418]  c1355bd8 f644c0e0 c1499c3d f5ff96e0 f644fed4 00000006 f5ff96e0 00000286
[    4.186579]  f644fedc c107922b f644feec 00000286 f5ff9460 f5ff9700 f644ff10 c135839e
[    4.186739] Call Trace:
[    4.186802]  [<c1365173>] sdhci_set_ios+0x1c3/0x340
[    4.186883]  [<c1355bd8>] mmc_gate_clock+0x68/0x120
[    4.186963]  [<c1499c3d>] ? _raw_spin_unlock_irqrestore+0x4d/0x60
[    4.187052]  [<c107922b>] ? trace_hardirqs_on+0xb/0x10
[    4.187134]  [<c135839e>] mmc_host_clk_gate_delayed+0xbe/0x130
[    4.187219]  [<c105ec09>] ? process_one_work+0xf9/0x5b0
[    4.187300]  [<c135841d>] mmc_host_clk_gate_work+0xd/0x10
[    4.187379]  [<c105ec82>] process_one_work+0x172/0x5b0
[    4.187457]  [<c105ec09>] ? process_one_work+0xf9/0x5b0
[    4.187538]  [<c1358410>] ? mmc_host_clk_gate_delayed+0x130/0x130
[    4.187625]  [<c105f3c8>] worker_thread+0x118/0x330
[    4.187700]  [<c1496cee>] ? preempt_schedule+0x2e/0x50
[    4.187779]  [<c105f2b0>] ? rescuer_thread+0x1f0/0x1f0
[    4.187857]  [<c1062cf4>] kthread+0x74/0x80
[    4.187931]  [<c1062c80>] ? __init_kthread_worker+0x60/0x60
[    4.188015]  [<c149acfa>] kernel_thread_helper+0x6/0xd
[    4.188079] Code: 81 fa 00 00 04 00 0f 84 a7 00 00 00 7f 21 81 fa 80 00 00 00 0f 84 92 00 00 00 81 fa 00 00 0
[    4.188780] EIP: [<c136364e>] sdhci_set_power+0x3e/0xd0 SS:ESP 0068:f644fe94
[    4.188898] ---[ end trace a7b23eecc71777e4 ]---

This BUG() comes from the fact that ios.power_mode was still in previous
value (MMC_POWER_ON) and ios.vdd was set to zero.

We prevent these by inhibiting the clock gating while we update the ios
structure.

Both problems can be reproduced by simply running the device in a reboot
loop.
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Chris Ball <cjb@laptop.org>
Cc: <stable@kernel.org>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/core/core.c

@@ -728,15 +728,17 @@ static inline void mmc_set_ios(struct mmc_host *host)
  */
 void mmc_set_chip_select(struct mmc_host *host, int mode)
 {
+	mmc_host_clk_hold(host);
 	host->ios.chip_select = mode;
 	mmc_set_ios(host);
+	mmc_host_clk_release(host);
 }
 
 /*
  * Sets the host clock to the highest possible frequency that
  * is below "hz".
  */
-void mmc_set_clock(struct mmc_host *host, unsigned int hz)
+static void __mmc_set_clock(struct mmc_host *host, unsigned int hz)
 {
 	WARN_ON(hz < host->f_min);
 
@@ -747,6 +749,13 @@ void mmc_set_clock(struct mmc_host *host, unsigned int hz)
 	mmc_set_ios(host);
 }
 
+void mmc_set_clock(struct mmc_host *host, unsigned int hz)
+{
+	mmc_host_clk_hold(host);
+	__mmc_set_clock(host, hz);
+	mmc_host_clk_release(host);
+}
+
 #ifdef CONFIG_MMC_CLKGATE
 /*
  * This gates the clock by setting it to 0 Hz.
@@ -779,7 +788,7 @@ void mmc_ungate_clock(struct mmc_host *host)
 	if (host->clk_old) {
 		BUG_ON(host->ios.clock);
 		/* This call will also set host->clk_gated to false */
-		mmc_set_clock(host, host->clk_old);
+		__mmc_set_clock(host, host->clk_old);
 	}
 }
 
@@ -807,8 +816,10 @@ void mmc_set_ungated(struct mmc_host *host)
  */
 void mmc_set_bus_mode(struct mmc_host *host, unsigned int mode)
 {
+	mmc_host_clk_hold(host);
 	host->ios.bus_mode = mode;
 	mmc_set_ios(host);
+	mmc_host_clk_release(host);
 }
 
 /*
@@ -816,8 +827,10 @@ void mmc_set_bus_mode(struct mmc_host *host, unsigned int mode)
  */
 void mmc_set_bus_width(struct mmc_host *host, unsigned int width)
 {
+	mmc_host_clk_hold(host);
 	host->ios.bus_width = width;
 	mmc_set_ios(host);
+	mmc_host_clk_release(host);
 }
 
 /**
@@ -1015,8 +1028,10 @@ u32 mmc_select_voltage(struct mmc_host *host, u32 ocr)
 
 		ocr &= 3 << bit;
 
+		mmc_host_clk_hold(host);
 		host->ios.vdd = bit;
 		mmc_set_ios(host);
+		mmc_host_clk_release(host);
 	} else {
 		pr_warning("%s: host doesn't support card's voltages\n",
 				mmc_hostname(host));
@@ -1063,8 +1078,10 @@ int mmc_set_signal_voltage(struct mmc_host *host, int signal_voltage, bool cmd11
  */
 void mmc_set_timing(struct mmc_host *host, unsigned int timing)
 {
+	mmc_host_clk_hold(host);
 	host->ios.timing = timing;
 	mmc_set_ios(host);
+	mmc_host_clk_release(host);
 }
 
 /*
@@ -1072,8 +1089,10 @@ void mmc_set_timing(struct mmc_host *host, unsigned int timing)
  */
 void mmc_set_driver_type(struct mmc_host *host, unsigned int drv_type)
 {
+	mmc_host_clk_hold(host);
 	host->ios.drv_type = drv_type;
 	mmc_set_ios(host);
+	mmc_host_clk_release(host);
 }
 
 /*
@@ -1091,6 +1110,8 @@ static void mmc_power_up(struct mmc_host *host)
 {
 	int bit;
 
+	mmc_host_clk_hold(host);
+
 	/* If ocr is set, we use it */
 	if (host->ocr)
 		bit = ffs(host->ocr) - 1;
@@ -1126,10 +1147,14 @@ static void mmc_power_up(struct mmc_host *host)
 	 * time required to reach a stable voltage.
 	 */
 	mmc_delay(10);
+
+	mmc_host_clk_release(host);
 }
 
 static void mmc_power_off(struct mmc_host *host)
 {
+	mmc_host_clk_hold(host);
+
 	host->ios.clock = 0;
 	host->ios.vdd = 0;
 
@@ -1147,6 +1172,8 @@ static void mmc_power_off(struct mmc_host *host)
 	host->ios.bus_width = MMC_BUS_WIDTH_1;
 	host->ios.timing = MMC_TIMING_LEGACY;
 	mmc_set_ios(host);
+
+	mmc_host_clk_release(host);
 }
 
 /*