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clk: fractional-divider: Introduce POWER_OF_TWO_PS flag

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The newly introduced POWER_OF_TWO_PS flag, when set, makes the flow
to skip the assumption that the caller will use an additional 2^scale
prescaler to get the desired clock rate.

Reported-by: Liu Ying <victor.liu@nxp.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210812170025.67074-3-andriy.shevchenko@linux.intel.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
This commit is contained in:
Andy Shevchenko 2021-08-12 20:00:24 +03:00 committed by Stephen Boyd
parent 928f9e2686
commit 82f53f9ee5
4 changed files with 17 additions and 7 deletions
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4
drivers/acpi/acpi_lpss.c
View File

@ -434,8 +434,8 @@ static int register_device_clock(struct acpi_device *adev,
if (!clk_name)
return -ENOMEM;
clk = clk_register_fractional_divider(NULL, clk_name, parent,
0, prv_base,
1, 15, 16, 15, 0, NULL);
CLK_FRAC_DIVIDER_POWER_OF_TWO_PS,
prv_base, 1, 15, 16, 15, 0, NULL);
parent = clk_name;
clk_name = kasprintf(GFP_KERNEL, "%s-update", devname);

6
drivers/clk/clk-fractional-divider.c
View File

@ -76,16 +76,18 @@ void clk_fractional_divider_general_approximation(struct clk_hw *hw,
unsigned long *m, unsigned long *n)
{
struct clk_fractional_divider *fd = to_clk_fd(hw);
unsigned long scale;
/*
* Get rate closer to *parent_rate to guarantee there is no overflow
* for m and n. In the result it will be the nearest rate left shifted
* by (scale - fd->nwidth) bits.
*/
scale = fls_long(*parent_rate / rate - 1);
if (fd->flags & CLK_FRAC_DIVIDER_POWER_OF_TWO_PS) {
unsigned long scale = fls_long(*parent_rate / rate - 1);
if (scale > fd->nwidth)
rate <<= scale - fd->nwidth;
}
rational_best_approximation(rate, *parent_rate,
GENMASK(fd->mwidth - 1, 0), GENMASK(fd->nwidth - 1, 0),

3
drivers/mfd/intel-lpss.c
View File

@ -301,7 +301,8 @@ static int intel_lpss_register_clock_divider(struct intel_lpss *lpss,
snprintf(name, sizeof(name), "%s-div", devname);
tmp = clk_register_fractional_divider(NULL, name, __clk_get_name(tmp),
0, lpss->priv, 1, 15, 16, 15, 0,
CLK_FRAC_DIVIDER_POWER_OF_TWO_PS,
lpss->priv, 1, 15, 16, 15, 0,
NULL);
if (IS_ERR(tmp))
return PTR_ERR(tmp);

7
include/linux/clk-provider.h
View File

@ -1001,6 +1001,12 @@ struct clk_hw *devm_clk_hw_register_fixed_factor(struct device *dev,
* CLK_FRAC_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_FRAC_DIVIDER_POWER_OF_TWO_PS - By default the resulting fraction might
* be saturated and the caller will get quite far from the good enough
* approximation. Instead the caller may require, by setting this flag,
* to shift left by a few bits in case, when the asked one is quite small
* to satisfy the desired range of denominator. It assumes that on the
* caller's side the power-of-two capable prescaler exists.
*/
struct clk_fractional_divider {
struct clk_hw hw;
@ -1022,6 +1028,7 @@ struct clk_fractional_divider {
#define CLK_FRAC_DIVIDER_ZERO_BASED BIT(0)
#define CLK_FRAC_DIVIDER_BIG_ENDIAN BIT(1)
#define CLK_FRAC_DIVIDER_POWER_OF_TWO_PS BIT(2)
struct clk *clk_register_fractional_divider(struct device *dev,
const char *name, const char *parent_name, unsigned long flags,