clk: sunxi: sun9i-mmc: Implement reset callback for reset controls

commit 61d2f2a0 upstream.

Our MMC host driver now issues a reset, instead of just deasserting
the reset control, since commit c34eda69 ("mmc: sunxi: Reset the
device at probe time"). The sun9i-mmc clock driver does not support
this, and will fail, which results in MMC not probing.

This patch implements the reset callback by asserting the reset control,
then deasserting it after a small delay.

Fixes: 7a6fca87 ("clk: sunxi: Add driver for A80 MMC config clocks/resets")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/20171218035751.20661-1-wens@csie.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/clk/sunxi/clk-sun9i-mmc.c

@@ -16,6 +16,7 @@
 
 #include <linux/clk.h>
 #include <linux/clk-provider.h>
+#include <linux/delay.h>
 #include <linux/init.h>
 #include <linux/of.h>
 #include <linux/of_device.h>
@@ -83,9 +84,20 @@ static int sun9i_mmc_reset_deassert(struct reset_controller_dev *rcdev,
 	return 0;
 }
 
+static int sun9i_mmc_reset_reset(struct reset_controller_dev *rcdev,
+				 unsigned long id)
+{
+	sun9i_mmc_reset_assert(rcdev, id);
+	udelay(10);
+	sun9i_mmc_reset_deassert(rcdev, id);
+
+	return 0;
+}
+
 static const struct reset_control_ops sun9i_mmc_reset_ops = {
 	.assert		= sun9i_mmc_reset_assert,
 	.deassert	= sun9i_mmc_reset_deassert,
+	.reset		= sun9i_mmc_reset_reset,
 };
 
 static int sun9i_a80_mmc_config_clk_probe(struct platform_device *pdev)