[PATCH] clk: canaan: Clear rate fields before reprogramming dividers

[David Carlier <devnexen@gmail.com>]

The rate set_rate helpers perform a read-modify-write on the divider
and multiplier registers but only ever OR the new value in, without
first masking off the existing field. The first write after reset lands
on a zeroed field and looks correct, but any later reprogramming leaves
the old bits set: the field becomes the bitwise OR of the previous and
new encodings, corrupting the divider or multiplier.

Mask off each field before writing the new value so reprogramming a
clock to a different rate produces the intended register contents.

Fixes: a7b7c7c6c016 ("clk: canaan: Add clock driver for Canaan K230")
Signed-off-by: David Carlier <devnexen@gmail.com>
---
 drivers/clk/clk-k230.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/clk/clk-k230.c b/drivers/clk/clk-k230.c
index cfc437038e4e..f34a3e6d3bca 100644
--- a/drivers/clk/clk-k230.c
+++ b/drivers/clk/clk-k230.c
@@ -2227,6 +2227,7 @@ static int k230_clk_set_rate_mul(struct clk_hw *hw, unsigned long rate,
 	guard(spinlock)(rate_self->lock);
 
 	mul_reg = readl(rate_self->reg + clk->mul_reg_off);
+	mul_reg &= ~(rate_self->mul_mask << rate_self->mul_shift);
 	mul_reg |= ((mul - 1) & rate_self->mul_mask) << (rate_self->mul_shift);
 	mul_reg |= BIT(rate_self->write_enable_bit);
 	writel(mul_reg, rate_self->reg + clk->mul_reg_off);
@@ -2257,6 +2258,7 @@ static int k230_clk_set_rate_div(struct clk_hw *hw, unsigned long rate,
 	guard(spinlock)(rate_self->lock);
 
 	div_reg = readl(rate_self->reg + clk->div_reg_off);
+	div_reg &= ~(rate_self->div_mask << rate_self->div_shift);
 	div_reg |= ((div - 1) & rate_self->div_mask) << (rate_self->div_shift);
 	div_reg |= BIT(rate_self->write_enable_bit);
 	writel(div_reg, rate_self->reg + clk->div_reg_off);
@@ -2287,11 +2289,13 @@ static int k230_clk_set_rate_mul_div(struct clk_hw *hw, unsigned long rate,
 	guard(spinlock)(rate_self->lock);
 
 	div_reg = readl(rate_self->reg + clk->div_reg_off);
+	div_reg &= ~(rate_self->div_mask << rate_self->div_shift);
 	div_reg |= ((div - 1) & rate_self->div_mask) << (rate_self->div_shift);
 	div_reg |= BIT(rate_self->write_enable_bit);
 	writel(div_reg, rate_self->reg + clk->div_reg_off);
 
 	mul_reg = readl(rate_self->reg + clk->mul_reg_off);
+	mul_reg &= ~(rate_self->mul_mask << rate_self->mul_shift);
 	mul_reg |= ((mul - 1) & rate_self->mul_mask) << (rate_self->mul_shift);
 	mul_reg |= BIT(rate_self->write_enable_bit);
 	writel(mul_reg, rate_self->reg + clk->mul_reg_off);
-- 
2.53.0