When doing excessive hotplug, e.g., repeated insert/eject operations,
the hardware may get confused to a point where no CMDTIMEOUT/CMDRESPEND
interrupts are generated any more.  As a result requests get stuck, e.g.:

[  360.351562] INFO: task kworker/u:0:5 blocked for more than 120 seconds.
[  360.351562] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[  360.359375] kworker/u:0   D c020c2b4     0     5      2 0x00000000
[  360.367187] Backtrace:
[  360.367187] [<c020bfb0>] (schedule+0x0/0x340) from [<c020c480>] (schedule_timeout+0x20/0x190)
[  360.375000]  r8:c702fd70 r7:00000002 r6:c702e000 r5:c702fdc4 r4:7fffffff
[  360.375000] r3:c701e040
[  360.382812] [<c020c460>] (schedule_timeout+0x0/0x190) from [<c020be78>] (wait_for_common+0xc4/0x150)
[  360.390625]  r6:c702e000 r5:c702fdc4 r4:7fffffff
[  360.390625] [<c020bdb4>] (wait_for_common+0x0/0x150) from [<c020bfac>] (wait_for_completion+0x18/0x1c)
[  360.398437] [<c020bf94>] (wait_for_completion+0x0/0x1c) from [<c0185590>] (mmc_wait_for_req+0x214/0x234)
[  360.406250] [<c018537c>] (mmc_wait_for_req+0x0/0x234) from [<c01889d0>] (mmc_sd_switch+0xfc/0x114)
[  360.414062]  r7:c702fe4c r6:c702fe20 r5:c7179800 r4:00fffff0
[  360.421875] [<c01888d4>] (mmc_sd_switch+0x0/0x114) from [<c0187f70>] (mmc_sd_setup_card+0x260/0x384)
[  360.429687] [<c0187d10>] (mmc_sd_setup_card+0x0/0x384) from [<c01885e0>] (mmc_sd_init_card+0x13c/0x1e0)
[  360.437500] [<c01884a4>] (mmc_sd_init_card+0x0/0x1e0) from [<c01887a8>] (mmc_attach_sd+0x124/0x1a8)
[  360.445312]  r8:c02db404 r7:ffffff92 r6:c702ff34 r5:c6007da8 r4:c6007c00
[  360.453125] [<c0188684>] (mmc_attach_sd+0x0/0x1a8) from [<c0185140>] (mmc_rescan+0x248/0x2f0)
[  360.460937]  r5:c6007da8 r4:c6007c00
[  360.468750] [<c0184ef8>] (mmc_rescan+0x0/0x2f0) from [<c00467f0>] (process_one_work+0x1ec/0x318)
[  360.476562]  r7:c6007da8 r6:00000000 r5:c710ec00 r4:c701bde0
[  360.484375] [<c0046604>] (process_one_work+0x0/0x318) from [<c0047fb0>] (worker_thread+0x1b0/0x2cc)
[  360.492187] [<c0047e00>] (worker_thread+0x0/0x2cc) from [<c004b338>] (kthread+0x8c/0x94)
[  360.500000] [<c004b2ac>] (kthread+0x0/0x94) from [<c0037fc4>] (do_exit+0x0/0x590)
[  360.507812]  r7:00000013 r6:c0037fc4 r5:c004b2ac r4:c7021f00

This patch addresses this problem by introducing timeouts for outstanding
interrupts. If a hardware interrupt is missing, a soft reset will be
performed to bring the hardware back to a working state.
Tested with the SDHI hardware block in sh7372 / AP4EVB.
Signed-off-by: Arnd Hannemann <arnd@arndnet.de>
Signed-off-by: Chris Ball <cjb@laptop.org>