[PATCH v4 11/17] clk: at91: clk-sam9x60-pll: add notifier for div part of PLL

From: Claudiu Beznea
Date: Thu Sep 23 2021 - 09:21:48 EST

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SAM9X60's PLL which is also part of SAMA7G5 is composed of 2 parts:
one fractional part and one divider. On SAMA7G5 the CPU PLL could be
changed at run-time to implement DVFS. The hardware clock tree on
SAMA7G5 for CPU PLL is as follows:

+---- div1 ----------------> cpuck
|
FRAC PLL ---> DIV PLL -+-> prescaler ---> div0 ---> mck0

The div1 block is not implemented in Linux; on prescaler block it has
been discovered a bug on some scenarios and will be removed from Linux
in next commits. Thus, the final clock tree that will be used in Linux
will be as follows:

+-----------> cpuck
|
FRAC PLL ---> DIV PLL -+-> div0 ---> mck0

It has been proposed in [1] to not introduce a new CPUFreq driver but
to overload the proper clock drivers with proper operation such that
cpufreq-dt to be used. To accomplish this DIV PLL and div0 implement
clock notifiers which applies safe dividers before FRAC PLL is changed.
The current commit treats only the DIV PLL by adding a notifier that
sets a safe divider on PRE_RATE_CHANGE events. The safe divider is
provided by initialization clock code (sama7g5.c). The div0 is treated
in next commits (to keep the changes as clean as possible).

[1] https://lore.kernel.org/lkml/20210105104426.4tmgc2l3vyicwedd@vireshk-i7/

Signed-off-by: Claudiu Beznea <claudiu.beznea@xxxxxxxxxxxxx>
---
drivers/clk/at91/clk-sam9x60-pll.c | 102 ++++++++++++++++++++++-------
drivers/clk/at91/pmc.h | 3 +-
drivers/clk/at91/sam9x60.c | 6 +-
drivers/clk/at91/sama7g5.c | 13 +++-
4 files changed, 95 insertions(+), 29 deletions(-)

diff --git a/drivers/clk/at91/clk-sam9x60-pll.c b/drivers/clk/at91/clk-sam9x60-pll.c
index a73d7c96ce1d..d757003004cb 100644
--- a/drivers/clk/at91/clk-sam9x60-pll.c
+++ b/drivers/clk/at91/clk-sam9x60-pll.c
@@ -5,6 +5,7 @@
*/

#include <linux/bitfield.h>
+#include <linux/clk.h>
#include <linux/clk-provider.h>
#include <linux/clkdev.h>
#include <linux/clk/at91_pmc.h>
@@ -47,12 +48,15 @@ struct sam9x60_div {
struct sam9x60_pll_core core;
struct at91_clk_pms pms;
u8 div;
+ u8 safe_div;
};

#define to_sam9x60_pll_core(hw) container_of(hw, struct sam9x60_pll_core, hw)
#define to_sam9x60_frac(core) container_of(core, struct sam9x60_frac, core)
#define to_sam9x60_div(core) container_of(core, struct sam9x60_div, core)

+static struct sam9x60_div *notifier_div;
+
static inline bool sam9x60_pll_ready(struct regmap *regmap, int id)
{
unsigned int status;
@@ -329,6 +333,26 @@ static const struct clk_ops sam9x60_frac_pll_ops_chg = {
.restore_context = sam9x60_frac_pll_restore_context,
};

+/* This function should be called with spinlock acquired. */
+static void sam9x60_div_pll_set_div(struct sam9x60_pll_core *core, u32 div,
+ bool enable)
+{
+ struct regmap *regmap = core->regmap;
+ u32 ena_msk = enable ? core->layout->endiv_mask : 0;
+ u32 ena_val = enable ? (1 << core->layout->endiv_shift) : 0;
+
+ regmap_update_bits(regmap, AT91_PMC_PLL_CTRL0,
+ core->layout->div_mask | ena_msk,
+ (div << core->layout->div_shift) | ena_val);
+
+ regmap_update_bits(regmap, AT91_PMC_PLL_UPDT,
+ AT91_PMC_PLL_UPDT_UPDATE | AT91_PMC_PLL_UPDT_ID_MSK,
+ AT91_PMC_PLL_UPDT_UPDATE | core->id);
+
+ while (!sam9x60_pll_ready(regmap, core->id))
+ cpu_relax();
+}
+
static int sam9x60_div_pll_set(struct sam9x60_pll_core *core)
{
struct sam9x60_div *div = to_sam9x60_div(core);
@@ -346,17 +370,7 @@ static int sam9x60_div_pll_set(struct sam9x60_pll_core *core)
if (!!(val & core->layout->endiv_mask) && cdiv == div->div)
goto unlock;

- regmap_update_bits(regmap, AT91_PMC_PLL_CTRL0,
- core->layout->div_mask | core->layout->endiv_mask,
- (div->div << core->layout->div_shift) |
- (1 << core->layout->endiv_shift));
-
- regmap_update_bits(regmap, AT91_PMC_PLL_UPDT,
- AT91_PMC_PLL_UPDT_UPDATE | AT91_PMC_PLL_UPDT_ID_MSK,
- AT91_PMC_PLL_UPDT_UPDATE | core->id);
-
- while (!sam9x60_pll_ready(regmap, core->id))
- cpu_relax();
+ sam9x60_div_pll_set_div(core, div->div, 1);

unlock:
spin_unlock_irqrestore(core->lock, flags);
@@ -502,16 +516,7 @@ static int sam9x60_div_pll_set_rate_chg(struct clk_hw *hw, unsigned long rate,
if (cdiv == div->div)
goto unlock;

- regmap_update_bits(regmap, AT91_PMC_PLL_CTRL0,
- core->layout->div_mask,
- (div->div << core->layout->div_shift));
-
- regmap_update_bits(regmap, AT91_PMC_PLL_UPDT,
- AT91_PMC_PLL_UPDT_UPDATE | AT91_PMC_PLL_UPDT_ID_MSK,
- AT91_PMC_PLL_UPDT_UPDATE | core->id);
-
- while (!sam9x60_pll_ready(regmap, core->id))
- cpu_relax();
+ sam9x60_div_pll_set_div(core, div->div, 0);

unlock:
spin_unlock_irqrestore(core->lock, irqflags);
@@ -538,6 +543,48 @@ static void sam9x60_div_pll_restore_context(struct clk_hw *hw)
sam9x60_div_pll_set(core);
}

+static int sam9x60_div_pll_notifier_fn(struct notifier_block *notifier,
+ unsigned long code, void *data)
+{
+ struct sam9x60_div *div = notifier_div;
+ struct sam9x60_pll_core core = div->core;
+ struct regmap *regmap = core.regmap;
+ unsigned long irqflags;
+ u32 val, cdiv;
+ int ret = NOTIFY_DONE;
+
+ if (code != PRE_RATE_CHANGE)
+ return ret;
+
+ /*
+ * We switch to safe divider to avoid overclocking of other domains
+ * feed by us while the frac PLL (our parent) is changed.
+ */
+ div->div = div->safe_div;
+
+ spin_lock_irqsave(core.lock, irqflags);
+ regmap_update_bits(regmap, AT91_PMC_PLL_UPDT, AT91_PMC_PLL_UPDT_ID_MSK,
+ core.id);
+ regmap_read(regmap, AT91_PMC_PLL_CTRL0, &val);
+ cdiv = (val & core.layout->div_mask) >> core.layout->div_shift;
+
+ /* Stop if nothing changed. */
+ if (cdiv == div->safe_div)
+ goto unlock;
+
+ sam9x60_div_pll_set_div(&core, div->div, 0);
+ ret = NOTIFY_OK;
+
+unlock:
+ spin_unlock_irqrestore(core.lock, irqflags);
+
+ return ret;
+}
+
+static struct notifier_block sam9x60_div_pll_notifier = {
+ .notifier_call = sam9x60_div_pll_notifier_fn,
+};
+
static const struct clk_ops sam9x60_div_pll_ops = {
.prepare = sam9x60_div_pll_prepare,
.unprepare = sam9x60_div_pll_unprepare,
@@ -647,7 +694,8 @@ struct clk_hw * __init
sam9x60_clk_register_div_pll(struct regmap *regmap, spinlock_t *lock,
const char *name, const char *parent_name, u8 id,
const struct clk_pll_characteristics *characteristics,
- const struct clk_pll_layout *layout, u32 flags)
+ const struct clk_pll_layout *layout, u32 flags,
+ u32 safe_div)
{
struct sam9x60_div *div;
struct clk_hw *hw;
@@ -656,9 +704,13 @@ sam9x60_clk_register_div_pll(struct regmap *regmap, spinlock_t *lock,
unsigned int val;
int ret;

- if (id > PLL_MAX_ID || !lock)
+ /* We only support one changeable PLL. */
+ if (id > PLL_MAX_ID || !lock || (safe_div && notifier_div))
return ERR_PTR(-EINVAL);

+ if (safe_div >= PLL_DIV_MAX)
+ safe_div = PLL_DIV_MAX - 1;
+
div = kzalloc(sizeof(*div), GFP_KERNEL);
if (!div)
return ERR_PTR(-ENOMEM);
@@ -678,6 +730,7 @@ sam9x60_clk_register_div_pll(struct regmap *regmap, spinlock_t *lock,
div->core.layout = layout;
div->core.regmap = regmap;
div->core.lock = lock;
+ div->safe_div = safe_div;

spin_lock_irqsave(div->core.lock, irqflags);

@@ -693,6 +746,9 @@ sam9x60_clk_register_div_pll(struct regmap *regmap, spinlock_t *lock,
if (ret) {
kfree(div);
hw = ERR_PTR(ret);
+ } else if (div->safe_div) {
+ notifier_div = div;
+ clk_notifier_register(hw->clk, &sam9x60_div_pll_notifier);
}

return hw;
diff --git a/drivers/clk/at91/pmc.h b/drivers/clk/at91/pmc.h
index 45df094498ce..207ecccef29f 100644
--- a/drivers/clk/at91/pmc.h
+++ b/drivers/clk/at91/pmc.h
@@ -214,7 +214,8 @@ struct clk_hw * __init
sam9x60_clk_register_div_pll(struct regmap *regmap, spinlock_t *lock,
const char *name, const char *parent_name, u8 id,
const struct clk_pll_characteristics *characteristics,
- const struct clk_pll_layout *layout, u32 flags);
+ const struct clk_pll_layout *layout, u32 flags,
+ u32 safe_div);

struct clk_hw * __init
sam9x60_clk_register_frac_pll(struct regmap *regmap, spinlock_t *lock,
diff --git a/drivers/clk/at91/sam9x60.c b/drivers/clk/at91/sam9x60.c
index 5f6fa89571b7..5c264185f261 100644
--- a/drivers/clk/at91/sam9x60.c
+++ b/drivers/clk/at91/sam9x60.c
@@ -242,7 +242,7 @@ static void __init sam9x60_pmc_setup(struct device_node *np)
* This feeds CPU. It should not
* be disabled.
*/
- CLK_IS_CRITICAL | CLK_SET_RATE_GATE);
+ CLK_IS_CRITICAL | CLK_SET_RATE_GATE, 0);
if (IS_ERR(hw))
goto err_free;

@@ -260,7 +260,7 @@ static void __init sam9x60_pmc_setup(struct device_node *np)
&pll_div_layout,
CLK_SET_RATE_GATE |
CLK_SET_PARENT_GATE |
- CLK_SET_RATE_PARENT);
+ CLK_SET_RATE_PARENT, 0);
if (IS_ERR(hw))
goto err_free;

@@ -279,7 +279,7 @@ static void __init sam9x60_pmc_setup(struct device_node *np)
hw = at91_clk_register_master_div(regmap, "masterck_div",
"masterck_pres", &sam9x60_master_layout,
&mck_characteristics, &mck_lock,
- CLK_SET_RATE_GATE);
+ CLK_SET_RATE_GATE, 0);
if (IS_ERR(hw))
goto err_free;

diff --git a/drivers/clk/at91/sama7g5.c b/drivers/clk/at91/sama7g5.c
index 970135e19a75..ae52c10af040 100644
--- a/drivers/clk/at91/sama7g5.c
+++ b/drivers/clk/at91/sama7g5.c
@@ -127,6 +127,8 @@ static const struct clk_pll_characteristics pll_characteristics = {
* @t: clock type
* @f: clock flags
* @eid: export index in sama7g5->chws[] array
+ * @safe_div: intermediate divider need to be set on PRE_RATE_CHANGE
+ * notification
*/
static const struct {
const char *n;
@@ -136,6 +138,7 @@ static const struct {
unsigned long f;
u8 t;
u8 eid;
+ u8 safe_div;
} sama7g5_plls[][PLL_ID_MAX] = {
[PLL_ID_CPU] = {
{ .n = "cpupll_fracck",
@@ -156,7 +159,12 @@ static const struct {
.t = PLL_TYPE_DIV,
/* This feeds CPU. It should not be disabled. */
.f = CLK_IS_CRITICAL | CLK_SET_RATE_PARENT,
- .eid = PMC_CPUPLL, },
+ .eid = PMC_CPUPLL,
+ /*
+ * Safe div=15 should be safe even for switching b/w 1GHz and
+ * 90MHz (frac pll might go up to 1.2GHz).
+ */
+ .safe_div = 15, },
},

[PLL_ID_SYS] = {
@@ -967,7 +975,8 @@ static void __init sama7g5_pmc_setup(struct device_node *np)
sama7g5_plls[i][j].p, i,
sama7g5_plls[i][j].c,
sama7g5_plls[i][j].l,
- sama7g5_plls[i][j].f);
+ sama7g5_plls[i][j].f,
+ sama7g5_plls[i][j].safe_div);
break;

default:
--
2.25.1

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