Add CLK_DIVIDER_EVEN_INTEGERS flag to support divisor of 2, 4, 6, etc.
The same divisor can be done using a table, which would be big and
wasteful for a clock dividor of width 8 (256 entries).

Require increasing flags size from u8 to u16 because
CLK_DIVIDER_EVEN_INTEGERS is the eighth flag.

Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
---
 drivers/clk/clk-divider.c    | 12 +++++++++---
 include/linux/clk-provider.h | 11 +++++++----
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c
index a2c2b5203b0a..b6654c5c36d2 100644
--- a/drivers/clk/clk-divider.c
+++ b/drivers/clk/clk-divider.c
@@ -72,6 +72,8 @@ static unsigned int _get_maxdiv(const struct clk_div_table *table, u8 width,
 		return clk_div_mask(width);
 	if (flags & CLK_DIVIDER_POWER_OF_TWO)
 		return 1 << clk_div_mask(width);
+	if (flags & CLK_DIVIDER_EVEN_INTEGERS)
+		return 2 * (clk_div_mask(width) + 1);
 	if (table)
 		return _get_table_maxdiv(table, width);
 	return clk_div_mask(width) + 1;
@@ -97,6 +99,8 @@ static unsigned int _get_div(const struct clk_div_table *table,
 		return 1 << val;
 	if (flags & CLK_DIVIDER_MAX_AT_ZERO)
 		return val ? val : clk_div_mask(width) + 1;
+	if (flags & CLK_DIVIDER_EVEN_INTEGERS)
+		return 2 * (val + 1);
 	if (table)
 		return _get_table_div(table, val);
 	return val + 1;
@@ -122,6 +126,8 @@ static unsigned int _get_val(const struct clk_div_table *table,
 		return __ffs(div);
 	if (flags & CLK_DIVIDER_MAX_AT_ZERO)
 		return (div == clk_div_mask(width) + 1) ? 0 : div;
+	if (flags & CLK_DIVIDER_EVEN_INTEGERS)
+		return (div >> 1) - 1;
 	if (table)
 		return  _get_table_val(table, div);
 	return div - 1;
@@ -538,7 +544,7 @@ struct clk_hw *__clk_hw_register_divider(struct device *dev,
 		struct device_node *np, const char *name,
 		const char *parent_name, const struct clk_hw *parent_hw,
 		const struct clk_parent_data *parent_data, unsigned long flags,
-		void __iomem *reg, u8 shift, u8 width, u8 clk_divider_flags,
+		void __iomem *reg, u8 shift, u8 width, u16 clk_divider_flags,
 		const struct clk_div_table *table, spinlock_t *lock)
 {
 	struct clk_divider *div;
@@ -610,7 +616,7 @@ EXPORT_SYMBOL_GPL(__clk_hw_register_divider);
 struct clk *clk_register_divider_table(struct device *dev, const char *name,
 		const char *parent_name, unsigned long flags,
 		void __iomem *reg, u8 shift, u8 width,
-		u8 clk_divider_flags, const struct clk_div_table *table,
+		u16 clk_divider_flags, const struct clk_div_table *table,
 		spinlock_t *lock)
 {
 	struct clk_hw *hw;
@@ -664,7 +670,7 @@ struct clk_hw *__devm_clk_hw_register_divider(struct device *dev,
 		struct device_node *np, const char *name,
 		const char *parent_name, const struct clk_hw *parent_hw,
 		const struct clk_parent_data *parent_data, unsigned long flags,
-		void __iomem *reg, u8 shift, u8 width, u8 clk_divider_flags,
+		void __iomem *reg, u8 shift, u8 width, u16 clk_divider_flags,
 		const struct clk_div_table *table, spinlock_t *lock)
 {
 	struct clk_hw **ptr, *hw;
diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
index 4a537260f655..cb348e502e41 100644
--- a/include/linux/clk-provider.h
+++ b/include/linux/clk-provider.h
@@ -675,13 +675,15 @@ struct clk_div_table {
  * CLK_DIVIDER_BIG_ENDIAN - By default little endian register accesses are used
  *	for the divider register.  Setting this flag makes the register accesses
  *	big endian.
+ * CLK_DIVIDER_EVEN_INTEGERS - clock divisor is 2, 4, 6, 8, 10, etc.
+ *	Formula is 2 * (value read from hardware + 1).
  */
 struct clk_divider {
 	struct clk_hw	hw;
 	void __iomem	*reg;
 	u8		shift;
 	u8		width;
-	u8		flags;
+	u16		flags;
 	const struct clk_div_table	*table;
 	spinlock_t	*lock;
 };
@@ -697,6 +699,7 @@ struct clk_divider {
 #define CLK_DIVIDER_READ_ONLY		BIT(5)
 #define CLK_DIVIDER_MAX_AT_ZERO		BIT(6)
 #define CLK_DIVIDER_BIG_ENDIAN		BIT(7)
+#define CLK_DIVIDER_EVEN_INTEGERS	BIT(8)
 
 extern const struct clk_ops clk_divider_ops;
 extern const struct clk_ops clk_divider_ro_ops;
@@ -726,18 +729,18 @@ struct clk_hw *__clk_hw_register_divider(struct device *dev,
 		struct device_node *np, const char *name,
 		const char *parent_name, const struct clk_hw *parent_hw,
 		const struct clk_parent_data *parent_data, unsigned long flags,
-		void __iomem *reg, u8 shift, u8 width, u8 clk_divider_flags,
+		void __iomem *reg, u8 shift, u8 width, u16 clk_divider_flags,
 		const struct clk_div_table *table, spinlock_t *lock);
 struct clk_hw *__devm_clk_hw_register_divider(struct device *dev,
 		struct device_node *np, const char *name,
 		const char *parent_name, const struct clk_hw *parent_hw,
 		const struct clk_parent_data *parent_data, unsigned long flags,
-		void __iomem *reg, u8 shift, u8 width, u8 clk_divider_flags,
+		void __iomem *reg, u8 shift, u8 width, u16 clk_divider_flags,
 		const struct clk_div_table *table, spinlock_t *lock);
 struct clk *clk_register_divider_table(struct device *dev, const char *name,
 		const char *parent_name, unsigned long flags,
 		void __iomem *reg, u8 shift, u8 width,
-		u8 clk_divider_flags, const struct clk_div_table *table,
+		u16 clk_divider_flags, const struct clk_div_table *table,
 		spinlock_t *lock);
 /**
  * clk_register_divider - register a divider clock with the clock framework

-- 
2.44.0

Quoting Théo Lebrun (2024-04-10 10:12:33)
> index 4a537260f655..cb348e502e41 100644
> --- a/include/linux/clk-provider.h
> +++ b/include/linux/clk-provider.h
> @@ -675,13 +675,15 @@ struct clk_div_table {
>   * CLK_DIVIDER_BIG_ENDIAN - By default little endian register accesses are used
>   *     for the divider register.  Setting this flag makes the register accesses
>   *     big endian.
> + * CLK_DIVIDER_EVEN_INTEGERS - clock divisor is 2, 4, 6, 8, 10, etc.
> + *     Formula is 2 * (value read from hardware + 1).
>   */
>  struct clk_divider {
>         struct clk_hw   hw;
>         void __iomem    *reg;
>         u8              shift;
>         u8              width;
> -       u8              flags;
> +       u16             flags;

This can stay u8

>         const struct clk_div_table      *table;
>         spinlock_t      *lock;
>  };

We should add a kunit test.

Hello,

On Thu Apr 11, 2024 at 5:06 AM CEST, Stephen Boyd wrote:
> Quoting Théo Lebrun (2024-04-10 10:12:33)
> > index 4a537260f655..cb348e502e41 100644
> > --- a/include/linux/clk-provider.h
> > +++ b/include/linux/clk-provider.h
> > @@ -675,13 +675,15 @@ struct clk_div_table {
> >   * CLK_DIVIDER_BIG_ENDIAN - By default little endian register accesses are used
> >   *     for the divider register.  Setting this flag makes the register accesses
> >   *     big endian.
> > + * CLK_DIVIDER_EVEN_INTEGERS - clock divisor is 2, 4, 6, 8, 10, etc.
> > + *     Formula is 2 * (value read from hardware + 1).
> >   */
> >  struct clk_divider {
> >         struct clk_hw   hw;
> >         void __iomem    *reg;
> >         u8              shift;
> >         u8              width;
> > -       u8              flags;
> > +       u16             flags;
>
> This can stay u8

It is unclear to me why it can stay u8? __clk_hw_register_divider() puts
clk_divider_flags into flags field of struct clk_divider.
BIT(8) overflows u8.

>
> >         const struct clk_div_table      *table;
> >         spinlock_t      *lock;
> >  };
>
> We should add a kunit test.

Will look into how this works and try something for next revision. I
guess you are talking about adding clk_divider tests, not only tests
for this flag? I cannot find any existing kunit tests for clk_divider.

Thanks,

--
Théo Lebrun, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

Quoting Théo Lebrun (2024-04-11 03:14:09)
> Hello,
> 
> On Thu Apr 11, 2024 at 5:06 AM CEST, Stephen Boyd wrote:
> > Quoting Théo Lebrun (2024-04-10 10:12:33)
> > > index 4a537260f655..cb348e502e41 100644
> > > --- a/include/linux/clk-provider.h
> > > +++ b/include/linux/clk-provider.h
> > > @@ -675,13 +675,15 @@ struct clk_div_table {
> > >   * CLK_DIVIDER_BIG_ENDIAN - By default little endian register accesses are used
> > >   *     for the divider register.  Setting this flag makes the register accesses
> > >   *     big endian.
> > > + * CLK_DIVIDER_EVEN_INTEGERS - clock divisor is 2, 4, 6, 8, 10, etc.
> > > + *     Formula is 2 * (value read from hardware + 1).
> > >   */
> > >  struct clk_divider {
> > >         struct clk_hw   hw;
> > >         void __iomem    *reg;
> > >         u8              shift;
> > >         u8              width;
> > > -       u8              flags;
> > > +       u16             flags;
> >
> > This can stay u8
> 
> It is unclear to me why it can stay u8? __clk_hw_register_divider() puts
> clk_divider_flags into flags field of struct clk_divider.
> BIT(8) overflows u8.

Oh, I missed that part.

> 
> >
> > >         const struct clk_div_table      *table;
> > >         spinlock_t      *lock;
> > >  };
> >
> > We should add a kunit test.
> 
> Will look into how this works and try something for next revision. I
> guess you are talking about adding clk_divider tests, not only tests
> for this flag? I cannot find any existing kunit tests for clk_divider.
> 

Right, there aren't any tests today. Thanks.