mmc: dw_mmc: Avoid accessing registers in runtime suspended state

cat /sys/kernel/debug/mmc0/regs will hang up the system since
it's in runtime suspended state, so the genpd and biu_clk is
off. This patch fixes this problem by calling pm_runtime_get_sync
to wake it up before reading the registers.

Fixes: e9ed8835 ("mmc: dw_mmc: add runtime PM callback")
Cc: <stable@vger.kernel.org>
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/dw_mmc.c

@@ -165,6 +165,8 @@ static int dw_mci_regs_show(struct seq_file *s, void *v)
 {
 	struct dw_mci *host = s->private;
 
+	pm_runtime_get_sync(host->dev);
+
 	seq_printf(s, "STATUS:\t0x%08x\n", mci_readl(host, STATUS));
 	seq_printf(s, "RINTSTS:\t0x%08x\n", mci_readl(host, RINTSTS));
 	seq_printf(s, "CMD:\t0x%08x\n", mci_readl(host, CMD));
@@ -172,6 +174,8 @@ static int dw_mci_regs_show(struct seq_file *s, void *v)
 	seq_printf(s, "INTMASK:\t0x%08x\n", mci_readl(host, INTMASK));
 	seq_printf(s, "CLKENA:\t0x%08x\n", mci_readl(host, CLKENA));
 
+	pm_runtime_put_autosuspend(host->dev);
+
 	return 0;
 }