[PATCH V2 01/10] clk: clk-divider: add CLK_DIVIDER_ZERO_GATE clk support

Dong Aisheng
2017-12-20T14:27:58Z

On Thu, Nov 02, 2017 at 12:50:39AM -0700, Stephen Boyd wrote:
> On 07/13, Dong Aisheng wrote:
> > diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c
> > index 9bb472c..55f8c41 100644
> > --- a/drivers/clk/clk-divider.c
> > +++ b/drivers/clk/clk-divider.c
> > @@ -123,6 +123,9 @@ unsigned long divider_recalc_rate(struct clk_hw *hw, unsigned long parent_rate,
> > struct clk_divider *divider = to_clk_divider(hw);
> > unsigned int div;
> >
> > + if (flags & CLK_DIVIDER_ZERO_GATE && !val)
> > + return 0;
> > +
> > div = _get_div(table, val, flags, divider->width);
> > if (!div) {
> > WARN(!(flags & CLK_DIVIDER_ALLOW_ZERO),
> > @@ -141,8 +144,13 @@ static unsigned long clk_divider_recalc_rate(struct clk_hw *hw,
> > struct clk_divider *divider = to_clk_divider(hw);
> > unsigned int val;
> >
> > - val = clk_readl(divider->reg) >> divider->shift;
> > - val &= div_mask(divider->width);
> > + if ((divider->flags & CLK_DIVIDER_ZERO_GATE) &&
> > + !clk_hw_is_enabled(hw)) {
>
> This seems racy. Are we holding the register lock here?
>

Would you please clarify what type of racy you mean?

Currently it only protects register write between set_rate and enable/disable,
and other register read are not protected.
e.g. in recalc_rate and is_enabled.

And i did see similar users, e.g.
drivers/clk/sunxi-ng/ccu_mult.c

Should we still need protect them here?

> > + val = divider->cached_val;
> > + } else {
> > + val = clk_readl(divider->reg) >> divider->shift;
> > + val &= div_mask(divider->width);
> > + }
> >
> > return divider_recalc_rate(hw, parent_rate, val, divider->table,
> > divider->flags);
> > @@ -392,6 +400,12 @@ static int clk_divider_set_rate(struct clk_hw *hw, unsigned long rate,
> > value = divider_get_val(rate, parent_rate, divider->table,
> > divider->width, divider->flags);
> >
> > + if ((divider->flags & CLK_DIVIDER_ZERO_GATE) &&
> > + !clk_hw_is_enabled(hw)) {
>
> Same racy comment here.
>
> > + divider->cached_val = value;
> > + return 0;
> > + }
> > +
> > if (divider->lock)
> > spin_lock_irqsave(divider->lock, flags);
> > else
> > @@ -414,10 +428,85 @@ static int clk_divider_set_rate(struct clk_hw *hw, unsigned long rate,
> > return 0;
> > }
> >
> > +static int clk_divider_enable(struct clk_hw *hw)
> > +{
> > + struct clk_divider *divider = to_clk_divider(hw);
> > + unsigned long flags = 0;
> > + u32 val;
> > +
> > + if (!(divider->flags & CLK_DIVIDER_ZERO_GATE))
> > + return 0;
>
> This is not good. We will always jump to these functions on
> enable/disable for a divider although 99.9% of all dividers that
> exist won't need to run this code at all.
>

I absolutely understand this concern.

> Can you please move this logic into your own divider
> implementation? The flag can be added to the generic layer if
> necessary but I'd prefer to see this logic kept in the driver
> that uses it. If we get more than one driver doing the cached
> divider thing then we can think about moving it to the more
> generic place like here, but for now we should be able to keep
> this contained away from the basic types and handled by the
> quirky driver that needs it.
>

If only for above issue, how about invent a clk_divider_gate_ops
to separate the users of normal divider and zero gate divider:

diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c
index 4ed516c..b51f3f9 100644
--- a/drivers/clk/clk-divider.c
+++ b/drivers/clk/clk-divider.c
@@ -125,6 +125,9 @@ unsigned long divider_recalc_rate(struct clk_hw *hw, unsigned long parent_rate,

div = _get_div(table, val, flags, divider->width);
if (!div) {
+ if (flags & CLK_DIVIDER_ZERO_GATE)
+ return 0;
+
WARN(!(flags & CLK_DIVIDER_ALLOW_ZERO),
"%s: Zero divisor and CLK_DIVIDER_ALLOW_ZERO not set\n",
clk_hw_get_name(hw));
@@ -148,6 +151,23 @@ static unsigned long clk_divider_recalc_rate(struct clk_hw *hw,
divider->flags);
}

+static unsigned long clk_divider_gate_recalc_rate(struct clk_hw *hw,
+ unsigned long parent_rate)
+{
+ struct clk_divider *divider = to_clk_divider(hw);
+ unsigned int val;
+
+ if (!clk_hw_is_enabled(hw)) {
+ val = divider->cached_val;
+ } else {
+ val = clk_readl(divider->reg) >> divider->shift;
+ val &= div_mask(divider->width);
+ }
+
+ return divider_recalc_rate(hw, parent_rate, val, divider->table,
+ divider->flags);
+}
+
static bool _is_valid_table_div(const struct clk_div_table *table,
unsigned int div)
{
@@ -416,6 +436,89 @@ static int clk_divider_set_rate(struct clk_hw *hw, unsigned long rate,
return 0;
}

+static int clk_divider_gate_set_rate(struct clk_hw *hw, unsigned long rate,
+ unsigned long parent_rate)
+{
+ struct clk_divider *divider = to_clk_divider(hw);
+ int value;
+
+ if (!clk_hw_is_enabled(hw)) {
+ value = divider_get_val(rate, parent_rate, divider->table,
+ divider->width, divider->flags);
+ if (value < 0)
+ return value;
+
+ divider->cached_val = value;
+
+ return 0;
+ }
+
+ return clk_divider_set_rate(hw, rate, parent_rate);
+}
+
+static int clk_divider_enable(struct clk_hw *hw)
+{
+ struct clk_divider *divider = to_clk_divider(hw);
+ unsigned long uninitialized_var(flags);
+ u32 val;
+
+ if (!divider->cached_val) {
+ pr_err("%s: no valid preset rate\n", clk_hw_get_name(hw));
+ return -EINVAL;
+ }
+
+ if (divider->lock)
+ spin_lock_irqsave(divider->lock, flags);
+ else
+ __acquire(divider->lock);
+
+ /* restore div val */
+ val = clk_readl(divider->reg);
+ val |= divider->cached_val << divider->shift;
+ clk_writel(val, divider->reg);
+
+ if (divider->lock)
+ spin_unlock_irqrestore(divider->lock, flags);
+ else
+ __release(divider->lock);
+
+ return 0;
+}
+
+static void clk_divider_disable(struct clk_hw *hw)
+{
+ struct clk_divider *divider = to_clk_divider(hw);
+ unsigned long uninitialized_var(flags);
+ u32 val;
+
+ if (divider->lock)
+ spin_lock_irqsave(divider->lock, flags);
+ else
+ __acquire(divider->lock);
+
+ /* store the current div val */
+ val = clk_readl(divider->reg) >> divider->shift;
+ val &= div_mask(divider->width);
+ divider->cached_val = val;
+ clk_writel(0, divider->reg);
+
+ if (divider->lock)
+ spin_unlock_irqrestore(divider->lock, flags);
+ else
+ __release(divider->lock);
+}
+
+static int clk_divider_is_enabled(struct clk_hw *hw)
+{
+ struct clk_divider *divider = to_clk_divider(hw);
+ u32 val;
+
+ val = clk_readl(divider->reg) >> divider->shift;
+ val &= div_mask(divider->width);
+
+ return val ? 1 : 0;
+}
+
const struct clk_ops clk_divider_ops = {
.recalc_rate = clk_divider_recalc_rate,
.round_rate = clk_divider_round_rate,
@@ -423,6 +526,16 @@ const struct clk_ops clk_divider_ops = {
};
EXPORT_SYMBOL_GPL(clk_divider_ops);

+const struct clk_ops clk_divider_gate_ops = {
+ .recalc_rate = clk_divider_gate_recalc_rate,
+ .round_rate = clk_divider_round_rate,
+ .set_rate = clk_divider_gate_set_rate,
+ .enable = clk_divider_enable,
+ .disable = clk_divider_disable,
+ .is_enabled = clk_divider_is_enabled,
+};
+EXPORT_SYMBOL_GPL(clk_divider_gate_ops);
+
const struct clk_ops clk_divider_ro_ops = {
.recalc_rate = clk_divider_recalc_rate,
.round_rate = clk_divider_round_rate,
@@ -438,6 +551,7 @@ static struct clk_hw *_register_divider(struct device *dev, const char *name,
struct clk_divider *div;
struct clk_hw *hw;
struct clk_init_data init;
+ u32 val;
int ret;

if (clk_divider_flags & CLK_DIVIDER_HIWORD_MASK) {
@@ -455,6 +569,8 @@ static struct clk_hw *_register_divider(struct device *dev, const char *name,
init.name = name;
if (clk_divider_flags & CLK_DIVIDER_READ_ONLY)
init.ops = &clk_divider_ro_ops;
+ else if (clk_divider_flags & CLK_DIVIDER_ZERO_GATE)
+ init.ops = &clk_divider_gate_ops;
else
init.ops = &clk_divider_ops;
init.flags = flags | CLK_IS_BASIC;
@@ -470,6 +586,12 @@ static struct clk_hw *_register_divider(struct device *dev, const char *name,
div->hw.init = &init;
div->table = table;

+ if (div->flags & CLK_DIVIDER_ZERO_GATE) {
+ val = clk_readl(reg) >> shift;
+ val &= div_mask(width);
+ div->cached_val = val;
+ }
+
/* register the clock */
hw = &div->hw;
ret = clk_hw_register(dev, hw);
diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
index 7c925e6..5f33b73 100644
--- a/include/linux/clk-provider.h
+++ b/include/linux/clk-provider.h
@@ -358,6 +358,7 @@ struct clk_div_table {
* @shift: shift to the divider bit field
* @width: width of the divider bit field
* @table: array of value/divider pairs, last entry should have div = 0
+ * @cached_val: cached div hw value used for CLK_DIVIDER_ZERO_GATE
* @lock: register lock
*
* Clock with an adjustable divider affecting its output frequency. Implements
@@ -386,6 +387,12 @@ struct clk_div_table {
* CLK_DIVIDER_MAX_AT_ZERO - For dividers which are like CLK_DIVIDER_ONE_BASED
* except when the value read from the register is zero, the divisor is
* 2^width of the field.
+ * CLK_DIVIDER_ZERO_GATE - For dividers which are like CLK_DIVIDER_ONE_BASED
+ * when the value read from the register is zero, it means the divisor
+ * is gated. For this case, the cached_val will be used to store the
+ * intermediate div for the normal rate operation, like set_rate/get_rate/
+ * recalc_rate. When the divider is ungated, the driver will actually
+ * program the hardware to have the requested divider value.
*/
struct clk_divider {
struct clk_hw hw;
@@ -394,6 +401,7 @@ struct clk_divider {
u8 width;
u8 flags;
const struct clk_div_table *table;
+ u32 cached_val;
spinlock_t *lock;
};

@@ -406,6 +414,7 @@ struct clk_divider {
#define CLK_DIVIDER_ROUND_CLOSEST BIT(4)
#define CLK_DIVIDER_READ_ONLY BIT(5)
#define CLK_DIVIDER_MAX_AT_ZERO BIT(6)
+#define CLK_DIVIDER_ZERO_GATE BIT(7)

extern const struct clk_ops clk_divider_ops;
extern const struct clk_ops clk_divider_ro_ops;

Anyway, if you still think it's not proper, i can put it in platform
driver as you wish, just in the cost of a few duplicated codes.

> > +
> > + if (!divider->cached_val) {
> > + pr_err("%s: no valid preset rate\n", clk_hw_get_name(hw));
> > + return -EINVAL;
> > + }
> > +
> > + if (divider->lock)
> > + spin_lock_irqsave(divider->lock, flags);
> > + else
> > + __acquire(divider->lock);
> > +
> > + /* restore div val */
> > + val = clk_readl(divider->reg);
> > + val |= divider->cached_val << divider->shift;
> > + clk_writel(val, divider->reg);
> > +
> > + if (divider->lock)
> > + spin_unlock_irqrestore(divider->lock, flags);
> > + else
> > + __release(divider->lock);
> > +
> > + return 0;
> > +}
> > +
> > +static void clk_divider_disable(struct clk_hw *hw)
> > +{
> > + struct clk_divider *divider = to_clk_divider(hw);
> > + unsigned long flags = 0;
> > + u32 val;
> > +
> > + if (!(divider->flags & CLK_DIVIDER_ZERO_GATE))
> > + return;
> > +
> > + if (divider->lock)
> > + spin_lock_irqsave(divider->lock, flags);
> > + else
> > + __acquire(divider->lock);
> > +
> > + /* store the current div val */
> > + val = clk_readl(divider->reg) >> divider->shift;
> > + val &= div_mask(divider->width);
> > + divider->cached_val = val;
> > + clk_writel(0, divider->reg);
> > +
> > + if (divider->lock)
> > + spin_unlock_irqrestore(divider->lock, flags);
> > + else
> > + __release(divider->lock);
> > +}
> > +
> > +static int clk_divider_is_enabled(struct clk_hw *hw)
> > +{
> > + struct clk_divider *divider = to_clk_divider(hw);
> > + u32 val;
> > +
> > + if (!(divider->flags & CLK_DIVIDER_ZERO_GATE))
> > + return __clk_get_enable_count(hw->clk);
>
> The plan was to delete this API once OMAP stopped using it.
> clk_hw_is_enabled() doesn't work?

No, it did not work before because clk_hw_is_enabled will result
in the dead loop by calling .is_enabled() callback again.

That's why __clk_get_enable_count is used instead.

However, with above new patch method, this issue was gone.

>
> > +
> > + val = clk_readl(divider->reg) >> divider->shift;
> > + val &= div_mask(divider->width);
> > +
> > + return val ? 1 : 0;
> > +}
> > +
> > const struct clk_ops clk_divider_ops = {
> > .recalc_rate = clk_divider_recalc_rate,
> > .round_rate = clk_divider_round_rate,
> > .set_rate = clk_divider_set_rate,
> > + .enable = clk_divider_enable,
> > + .disable = clk_divider_disable,
> > + .is_enabled = clk_divider_is_enabled,
> > };
> > EXPORT_SYMBOL_GPL(clk_divider_ops);
> >
> > @@ -436,6 +525,7 @@ static struct clk_hw *_register_divider(struct device *dev, const char *name,
> > struct clk_divider *div;
> > struct clk_hw *hw;
> > struct clk_init_data init;
> > + u32 val;
> > int ret;
> >
> > if (clk_divider_flags & CLK_DIVIDER_HIWORD_MASK) {
> > @@ -468,6 +558,12 @@ static struct clk_hw *_register_divider(struct device *dev, const char *name,
> > div->hw.init = &init;
> > div->table = table;
> >
> > + if (div->flags & CLK_DIVIDER_ZERO_GATE) {
> > + val = clk_readl(reg) >> shift;
> > + val &= div_mask(width);
> > + div->cached_val = val;
> > + }
>
> What if it isn't on? Setting cached_val to 0 is ok?
>

If it isn't on, then the cache_val should be 0.
And recalc_rate will catch this case and return 0 as there's
no proper pre-set rate.

Regards
Dong Aisheng

> > +
> > /* register the clock */
> > hw = &div->hw;
> > ret = clk_hw_register(dev, hw);
>
> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
> a Linux Foundation Collaborative Project