[PATCH 4.2.y-ckt 168/218] clk-divider: make sure read-only dividers do not write to their register

[Kamal Mostafa]

4.2.8-ckt7 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Heiko Stuebner <heiko at sntech.de>

commit 50359819794b4a16ae35051cd80f2dab025f6019 upstream.

Commit e6d5e7d90be9 ("clk-divider: Fix READ_ONLY when divider > 1") removed
the special ops struct for read-only clocks and instead opted to handle
them inside the regular ops.

On the rk3368 this results in breakage as aclkm now gets set a value.
While it is the same divider value, the A53 core still doesn't like it,
which can result in the cpu ending up in a hang.
The reason being that "ACLKENMasserts one clock cycle before the rising
edge of ACLKM" and the clock should only be touched when STANDBYWFIL2
is asserted.

To fix this, reintroduce the read-only ops but do include the round_rate
callback. That way no writes that may be unsafe are done to the divider
register in any case.

The Rockchip use of the clk_divider_ops is adapted to this split again,
as is the nxp, lpc18xx-ccu driver that was included since the original
commit. On lpc18xx-ccu the divider seems to always be read-only
so only uses the new ops now.

Fixes: e6d5e7d90be9 ("clk-divider: Fix READ_ONLY when divider > 1")
Reported-by: Zhang Qing <zhangqing at rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko at sntech.de>
Signed-off-by: Stephen Boyd <sboyd at codeaurora.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/clk/clk-divider.c         | 11 ++++++++++-
 drivers/clk/nxp/clk-lpc18xx-ccu.c |  2 +-
 drivers/clk/rockchip/clk.c        |  4 +++-
 include/linux/clk-provider.h      |  1 +
 4 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c
index 706b578..79f5c78 100644
--- a/drivers/clk/clk-divider.c
+++ b/drivers/clk/clk-divider.c
@@ -412,6 +412,12 @@ const struct clk_ops clk_divider_ops = {
 };
 EXPORT_SYMBOL_GPL(clk_divider_ops);
 
+const struct clk_ops clk_divider_ro_ops = {
+	.recalc_rate = clk_divider_recalc_rate,
+	.round_rate = clk_divider_round_rate,
+};
+EXPORT_SYMBOL_GPL(clk_divider_ro_ops);
+
 static struct clk *_register_divider(struct device *dev, const char *name,
 		const char *parent_name, unsigned long flags,
 		void __iomem *reg, u8 shift, u8 width,
@@ -435,7 +441,10 @@ static struct clk *_register_divider(struct device *dev, const char *name,
 		return ERR_PTR(-ENOMEM);
 
 	init.name = name;
-	init.ops = &clk_divider_ops;
+	if (clk_divider_flags & CLK_DIVIDER_READ_ONLY)
+		init.ops = &clk_divider_ro_ops;
+	else
+		init.ops = &clk_divider_ops;
 	init.flags = flags | CLK_IS_BASIC;
 	init.parent_names = (parent_name ? &parent_name: NULL);
 	init.num_parents = (parent_name ? 1 : 0);
diff --git a/drivers/clk/nxp/clk-lpc18xx-ccu.c b/drivers/clk/nxp/clk-lpc18xx-ccu.c
index eeaee97..d27fd7a 100644
--- a/drivers/clk/nxp/clk-lpc18xx-ccu.c
+++ b/drivers/clk/nxp/clk-lpc18xx-ccu.c
@@ -209,7 +209,7 @@ static void lpc18xx_ccu_register_branch_gate_div(struct lpc18xx_clk_branch *bran
 		div->width = 1;
 
 		div_hw = &div->hw;
-		div_ops = &clk_divider_ops;
+		div_ops = &clk_divider_ro_ops;
 	}
 
 	branch->gate.reg = branch->offset + reg_base;
diff --git a/drivers/clk/rockchip/clk.c b/drivers/clk/rockchip/clk.c
index 051bfe8..a9bdfd7 100644
--- a/drivers/clk/rockchip/clk.c
+++ b/drivers/clk/rockchip/clk.c
@@ -90,7 +90,9 @@ static struct clk *rockchip_clk_register_branch(const char *name,
 		div->width = div_width;
 		div->lock = lock;
 		div->table = div_table;
-		div_ops = &clk_divider_ops;
+		div_ops = (div_flags & CLK_DIVIDER_READ_ONLY)
+						? &clk_divider_ro_ops
+						: &clk_divider_ops;
 	}
 
 	clk = clk_register_composite(NULL, name, parent_names, num_parents,
diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
index 78842f4..c707cfbe 100644
--- a/include/linux/clk-provider.h
+++ b/include/linux/clk-provider.h
@@ -362,6 +362,7 @@ struct clk_divider {
 #define CLK_DIVIDER_READ_ONLY		BIT(5)
 
 extern const struct clk_ops clk_divider_ops;
+extern const struct clk_ops clk_divider_ro_ops;
 
 unsigned long divider_recalc_rate(struct clk_hw *hw, unsigned long parent_rate,
 		unsigned int val, const struct clk_div_table *table,
-- 
2.7.4