mtd: spi-nor: Fix Cadence QSPI RCU Schedule Stall

The current Cadence QSPI driver sometimes caused a
"rcu_sched self-detected stall" while writing large files.

Stall Report:
'# mtd_debug write /dev/mtd1 0 48816464 blob.img
[ 1815.454227] rcu: INFO: rcu_sched self-detected stall on CPU
[ 1815.459789] rcu:     0-....: (2099 ticks this GP) idle=8c6/1/0x40000002
 softirq=6492/6492 fqs=935
[ 1815.468442] rcu:      (t=2100 jiffies g=8749 q=247)
	<snip> (abbreviated backtrace)
[ 1815.772086] [<c05a3ea0>] (cqspi_exec_flash_cmd) (cqspi_read_reg)
[ 1815.786203] [<c05a5488>] (cqspi_read_reg) from (read_sr)
[ 1815.803790] [<c05a0330>] (read_sr) from
	(spi_nor_wait_till_ready_with_timeout)
[ 1815.816610] [<c05a182c>] (spi_nor_wait_till_ready_with_timeout) from
	(spi_nor_write+0x104/0x1d0)
[ 1815.836791] [<c05a1a44>] (spi_nor_write) from (part_write+0x50/0x58)
	<snip>
[ 1815.997961] cadence-qspi ff809000.spi: Flash command execution timed out.
[ 1816.004733] error -110 reading SR
file_to_flash: write, size 0x2e8e150, n 0x2e8e150
write(): Connection timed out

This was caused by a tight loop in cqspi_wait_for_bit(). Fix by using
readl_relaxed_poll_timeout() which sleeps 10us while polling a register.

Fit onto 80 character line by truncating the bool clear parameter

Fixes: 14062341 ("mtd: spi-nor: Add driver for Cadence Quad SPI Flash Controller")
Signed-off-by: Thor Thayer <thor.thayer@linux.intel.com>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>

drivers/mtd/spi-nor/cadence-quadspi.c

@@ -13,6 +13,7 @@
 #include <linux/errno.h>
 #include <linux/interrupt.h>
 #include <linux/io.h>
+#include <linux/iopoll.h>
 #include <linux/jiffies.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
@@ -241,23 +242,13 @@ struct cqspi_driver_platdata {
 
 #define CQSPI_IRQ_STATUS_MASK		0x1FFFF
 
-static int cqspi_wait_for_bit(void __iomem *reg, const u32 mask, bool clear)
+static int cqspi_wait_for_bit(void __iomem *reg, const u32 mask, bool clr)
 {
-	unsigned long end = jiffies + msecs_to_jiffies(CQSPI_TIMEOUT_MS);
 	u32 val;
 
-	while (1) {
-		val = readl(reg);
-		if (clear)
-			val = ~val;
-		val &= mask;
-
-		if (val == mask)
-			return 0;
-
-		if (time_after(jiffies, end))
-			return -ETIMEDOUT;
-	}
+	return readl_relaxed_poll_timeout(reg, val,
+					  (((clr ? ~val : val) & mask) == mask),
+					  10, CQSPI_TIMEOUT_MS * 1000);
 }
 
 static bool cqspi_is_idle(struct cqspi_st *cqspi)