mmc: sdhci: request irq after sdhci_init() is called

Generally request_irq() should be called after hardware has been
initialized into a sane state.  However, sdhci driver currently calls
request_irq() before sdhci_init().  At least, the following kernel panic
seen on i.MX6 is caused by that.  The sdhci controller on i.MX6 may have
noisy glitch on DAT1 line, which will trigger SDIO interrupt handling
once request_irq() is called.  But at this point, the SDIO interrupt
handler host->sdio_irq_thread has not been registered yet.  Thus, we
see the NULL pointer access with wake_up_process(host->sdio_irq_thread)
in mmc_signal_sdio_irq().

sdhci-pltfm: SDHCI platform and OF driver helper
mmc0: no vqmmc regulator found
mmc0: no vmmc regulator found
Unable to handle kernel NULL pointer dereference at virtual address
00000000
pgd = 80004000
[00000000] *pgd=00000000
Internal error: Oops: 5 [wandboard-org#1] SMP ARM
Modules linked in:
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.10.0+ wandboard-org#3
task: 9f860000 ti: 9f862000 task.ti: 9f862000
PC is at wake_up_process+0xc/0x44
LR is at sdhci_irq+0x378/0x93c
...
Backtrace:
[<8004f75c>] (wake_up_process+0x0/0x44) from [<803fb698>]
(sdhci_irq+0x378/0x93c)
 r4:9fa68000 r3:00000001
[<803fb320>] (sdhci_irq+0x0/0x93c) from [<80075154>]
(handle_irq_event_percpu+0x54/0x19c)
[<80075100>] (handle_irq_event_percpu+0x0/0x19c) from [<800752ec>]
(handle_irq_event+0x50/0x70)
[<8007529c>] (handle_irq_event+0x0/0x70) from [<80078324>]
(handle_fasteoi_irq+0x9c/0x170)
 r5:00000001 r4:9f807900
[<80078288>] (handle_fasteoi_irq+0x0/0x170) from [<80074ac0>]
(generic_handle_irq+0x28/0x38)
 r5:8071fd64 r4:00000036
[<80074a98>] (generic_handle_irq+0x0/0x38) from [<8000ee34>]
(handle_IRQ+0x54/0xb4)
 r4:8072ab78 r3:00000140
[<8000ede0>] (handle_IRQ+0x0/0xb4) from [<80008600>]
(gic_handle_irq+0x30/0x64)
 r8:00000036 r7:a080e100 r6:9f863cd0 r5:8072acbc r4:a080e10c
r3:00000000
[<800085d0>] (gic_handle_irq+0x0/0x64) from [<8000e0c0>]
(__irq_svc+0x40/0x54)
...
---[ end trace e9af3588936b63f0 ]---
Kernel panic - not syncing: Fatal exception in interrupt

Fix the panic by simply reverse the calling sequence between
request_irq() and sdhci_init().

Signed-off-by: Shawn Guo <shawn.guo@freescale.com>

drivers/mmc/host/sdhci.c

@@ -3174,6 +3174,8 @@ int sdhci_add_host(struct sdhci_host *host)
 		host->tuning_timer.function = sdhci_tuning_timer;
 	}
 
+	sdhci_init(host, 0);
+
 	ret = request_irq(host->irq, sdhci_irq, IRQF_SHARED,
 		mmc_hostname(mmc), host);
 	if (ret) {
@@ -3182,8 +3184,6 @@ int sdhci_add_host(struct sdhci_host *host)
 		goto untasklet;
 	}
 
-	sdhci_init(host, 0);
-
 #ifdef CONFIG_MMC_DEBUG
 	sdhci_dumpregs(host);
 #endif