Revert "clocksource/drivers/timer_sun5i: Replace code by clocksource_mmio_init"

struct clocksource is also used by the clk notifier callback, to
unregister and re-register the clocksource with a different clock rate.
clocksource_mmio_init does not pass back a pointer to the struct used,
and the clk notifier callback assumes that the struct clocksource in
struct sun5i_timer_clksrc is valid. This results in a kernel NULL
pointer dereference when the hstimer clock is changed:

Unable to handle kernel NULL pointer dereference at virtual address 00000004
[<c03a4678>] (clocksource_unbind) from [<c03a46d4>] (clocksource_unregister+0x2c/0x44)
[<c03a46d4>] (clocksource_unregister) from [<c0a6f350>] (sun5i_rate_cb_clksrc+0x34/0x3c)
[<c0a6f350>] (sun5i_rate_cb_clksrc) from [<c035ea50>] (notifier_call_chain+0x44/0x84)
[<c035ea50>] (notifier_call_chain) from [<c035edc0>] (__srcu_notifier_call_chain+0x44/0x60)
[<c035edc0>] (__srcu_notifier_call_chain) from [<c035edf4>] (srcu_notifier_call_chain+0x18/0x20)
[<c035edf4>] (srcu_notifier_call_chain) from [<c0670174>] (__clk_notify+0x70/0x7c)
[<c0670174>] (__clk_notify) from [<c06702c0>] (clk_propagate_rate_change+0xa4/0xc4)
[<c06702c0>] (clk_propagate_rate_change) from [<c0670288>] (clk_propagate_rate_change+0x6c/0xc4)

Revert the commit for now. clocksource_mmio_init can be made to pass back
a pointer, but the code churn and usage of an inner struct might not be
worth it.

Fixes: 157dfadef832 ("clocksource/drivers/timer_sun5i: Replace code by clocksource_mmio_init")
Reported-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Cc: linux-sunxi@googlegroups.com
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/20161018054918.26855-1-wens@csie.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

drivers/clocksource/timer-sun5i.c

@@ -152,6 +152,13 @@ static irqreturn_t sun5i_timer_interrupt(int irq, void *dev_id)
 	return IRQ_HANDLED;
 }
 
+static cycle_t sun5i_clksrc_read(struct clocksource *clksrc)
+{
+	struct sun5i_timer_clksrc *cs = to_sun5i_timer_clksrc(clksrc);
+
+	return ~readl(cs->timer.base + TIMER_CNTVAL_LO_REG(1));
+}
+
 static int sun5i_rate_cb_clksrc(struct notifier_block *nb,
 				unsigned long event, void *data)
 {
@@ -210,8 +217,13 @@ static int __init sun5i_setup_clocksource(struct device_node *node,
 	writel(TIMER_CTL_ENABLE | TIMER_CTL_RELOAD,
 	       base + TIMER_CTL_REG(1));
 
-	ret = clocksource_mmio_init(base + TIMER_CNTVAL_LO_REG(1), node->name,
-				    rate, 340, 32, clocksource_mmio_readl_down);
+	cs->clksrc.name = node->name;
+	cs->clksrc.rating = 340;
+	cs->clksrc.read = sun5i_clksrc_read;
+	cs->clksrc.mask = CLOCKSOURCE_MASK(32);
+	cs->clksrc.flags = CLOCK_SOURCE_IS_CONTINUOUS;
+
+	ret = clocksource_register_hz(&cs->clksrc, rate);
 	if (ret) {
 		pr_err("Couldn't register clock source.\n");
 		goto err_remove_notifier;