[PATCH 0/3] renesas: r8a779g0: Add support for boost mode

[PATCH 0/3] renesas: r8a779g0: Add support for boost mode

[Geert Uytterhoeven]

	Hi all,

This patch series adds support for running the Cortex-A76 CPU cores on
R-Car V4H at 1.8 GHz (High Performance mode aka "boost mode").

The first patch adds boost support to the clock driver.
The second patch contains an RFC improvement for the clock driver.
The third patch describes the 1.8 GHz operating point in DT.

Thanks for your comments!

Geert Uytterhoeven (3):
  clk: renesas: r8a779g0: Add custom clock for PLL2
  clk: renesas: rcar-gen4: Add support for fractional multiplication
  arm64: dts: renesas: r8a779g0: Add Cortex-A76 1.8 GHz opp

 arch/arm64/boot/dts/renesas/r8a779g0.dtsi |   6 +
 drivers/clk/renesas/r8a779g0-cpg-mssr.c   |  14 +-
 drivers/clk/renesas/rcar-gen4-cpg.c       | 195 ++++++++++++++++++++++
 drivers/clk/renesas/rcar-gen4-cpg.h       |   1 +
 4 files changed, 209 insertions(+), 7 deletions(-)

-- 
2.25.1

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds

[PATCH 1/3] clk: renesas: r8a779g0: Add custom clock for PLL2

[Geert Uytterhoeven]

Currently the PLLs are modeled as fixed factor clocks, based on initial
settings.  However, enabling CPU boost clock rates requires increasing
the PLL clock rates.

Add a custom clock driver to model the PLL clocks on R-Car Gen4, and use
it for PLL2 on R-Car V4H.  This allows the Z clock (Cortex-A76 core
clock) to request PLL rate changes, and enable boost mode for the High
Performance mode.  For now this is limited to integer multiplication
modes.

Note that the definition for CPG_PLLxCR0_NI uses the value for R-Car V4H.
On R-Car S4-8, the integer and fractional multiplication fields are one
bit larger resp. smaller, but R-Car S4-8 does not support High
Performance mode.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
 drivers/clk/renesas/r8a779g0-cpg-mssr.c |  14 +--
 drivers/clk/renesas/rcar-gen4-cpg.c     | 156 ++++++++++++++++++++++++
 drivers/clk/renesas/rcar-gen4-cpg.h     |   1 +
 3 files changed, 164 insertions(+), 7 deletions(-)

diff --git a/drivers/clk/renesas/r8a779g0-cpg-mssr.c b/drivers/clk/renesas/r8a779g0-cpg-mssr.c
index 745ff9214fe8609d..48d9f34bbf37657a 100644
--- a/drivers/clk/renesas/r8a779g0-cpg-mssr.c
+++ b/drivers/clk/renesas/r8a779g0-cpg-mssr.c
@@ -66,13 +66,13 @@ static const struct cpg_core_clk r8a779g0_core_clks[] __initconst = {
 	DEF_INPUT("extalr",	CLK_EXTALR),
 
 	/* Internal Core Clocks */
-	DEF_BASE(".main", CLK_MAIN,	CLK_TYPE_GEN4_MAIN, CLK_EXTAL),
-	DEF_BASE(".pll1", CLK_PLL1,	CLK_TYPE_GEN4_PLL1, CLK_MAIN),
-	DEF_BASE(".pll2", CLK_PLL2,	CLK_TYPE_GEN4_PLL2, CLK_MAIN),
-	DEF_BASE(".pll3", CLK_PLL3,	CLK_TYPE_GEN4_PLL3, CLK_MAIN),
-	DEF_BASE(".pll4", CLK_PLL4,	CLK_TYPE_GEN4_PLL4, CLK_MAIN),
-	DEF_BASE(".pll5", CLK_PLL5,	CLK_TYPE_GEN4_PLL5, CLK_MAIN),
-	DEF_BASE(".pll6", CLK_PLL6,	CLK_TYPE_GEN4_PLL6, CLK_MAIN),
+	DEF_BASE(".main", CLK_MAIN,	CLK_TYPE_GEN4_MAIN,     CLK_EXTAL),
+	DEF_BASE(".pll1", CLK_PLL1,	CLK_TYPE_GEN4_PLL1,     CLK_MAIN),
+	DEF_BASE(".pll2", CLK_PLL2,	CLK_TYPE_GEN4_PLL2_VAR, CLK_MAIN),
+	DEF_BASE(".pll3", CLK_PLL3,	CLK_TYPE_GEN4_PLL3,     CLK_MAIN),
+	DEF_BASE(".pll4", CLK_PLL4,	CLK_TYPE_GEN4_PLL4,     CLK_MAIN),
+	DEF_BASE(".pll5", CLK_PLL5,	CLK_TYPE_GEN4_PLL5,     CLK_MAIN),
+	DEF_BASE(".pll6", CLK_PLL6,	CLK_TYPE_GEN4_PLL6,     CLK_MAIN),
 
 	DEF_FIXED(".pll1_div2",	CLK_PLL1_DIV2,	CLK_PLL1,	2, 1),
 	DEF_FIXED(".pll2_div2",	CLK_PLL2_DIV2,	CLK_PLL2,	2, 1),
diff --git a/drivers/clk/renesas/rcar-gen4-cpg.c b/drivers/clk/renesas/rcar-gen4-cpg.c
index e27832e5114fbdf0..c68d8b987054131b 100644
--- a/drivers/clk/renesas/rcar-gen4-cpg.c
+++ b/drivers/clk/renesas/rcar-gen4-cpg.c
@@ -17,6 +17,7 @@
 #include <linux/err.h>
 #include <linux/init.h>
 #include <linux/io.h>
+#include <linux/iopoll.h>
 #include <linux/slab.h>
 
 #include "renesas-cpg-mssr.h"
@@ -27,6 +28,152 @@ static const struct rcar_gen4_cpg_pll_config *cpg_pll_config __initdata;
 static unsigned int cpg_clk_extalr __initdata;
 static u32 cpg_mode __initdata;
 
+#define CPG_PLLECR		0x0820	/* PLL Enable Control Register */
+
+#define CPG_PLLECR_PLLST(n)	BIT(8 + ((n) < 3 ? (n) - 1 : \
+					 (n) > 3 ? (n) + 1 : n)) /* PLLn Circuit Status */
+
+#define CPG_PLL1CR0		0x830	/* PLLn Control Registers */
+#define CPG_PLL1CR1		0x8b0
+#define CPG_PLL2CR0		0x834
+#define CPG_PLL2CR1		0x8b8
+#define CPG_PLL3CR0		0x83c
+#define CPG_PLL3CR1		0x8c0
+#define CPG_PLL4CR0		0x844
+#define CPG_PLL4CR1		0x8c8
+#define CPG_PLL6CR0		0x84c
+#define CPG_PLL6CR1		0x8d8
+
+#define CPG_PLLxCR0_KICK	BIT(31)
+#define CPG_PLLxCR0_NI		GENMASK(27, 20)	/* Integer mult. factor */
+#define CPG_PLLxCR0_SSMODE	GENMASK(18, 16)	/* PLL mode */
+#define CPG_PLLxCR0_SSMODE_FM	BIT(18)	/* Fractional Multiplication */
+#define CPG_PLLxCR0_SSMODE_DITH	BIT(17) /* Frequency Dithering */
+#define CPG_PLLxCR0_SSMODE_CENT	BIT(16)	/* Center (vs. Down) Spread Dithering */
+#define CPG_PLLxCR0_SSFREQ	GENMASK(14, 8)	/* SSCG Modulation Frequency */
+#define CPG_PLLxCR0_SSDEPT	GENMASK(6, 0)	/* SSCG Modulation Depth */
+
+#define SSMODE_FM		BIT(2)	/* Fractional Multiplication */
+#define SSMODE_DITHER		BIT(1)	/* Frequency Dithering */
+#define SSMODE_CENTER		BIT(0)	/* Center (vs. Down) Spread Dithering */
+
+/* PLL Clocks */
+struct cpg_pll_clk {
+	struct clk_hw hw;
+	void __iomem *pllcr0_reg;
+	void __iomem *pllecr_reg;
+	u32 pllecr_pllst_mask;
+};
+
+#define to_pll_clk(_hw)   container_of(_hw, struct cpg_pll_clk, hw)
+
+static unsigned long cpg_pll_clk_recalc_rate(struct clk_hw *hw,
+					     unsigned long parent_rate)
+{
+	struct cpg_pll_clk *pll_clk = to_pll_clk(hw);
+	unsigned int mult;
+
+	mult = FIELD_GET(CPG_PLLxCR0_NI, readl(pll_clk->pllcr0_reg)) + 1;
+
+	return parent_rate * mult * 2;
+}
+
+static int cpg_pll_clk_determine_rate(struct clk_hw *hw,
+				      struct clk_rate_request *req)
+{
+	unsigned int min_mult, max_mult, mult;
+	unsigned long prate;
+
+	prate = req->best_parent_rate * 2;
+	min_mult = max(div64_ul(req->min_rate, prate), 1ULL);
+	max_mult = min(div64_ul(req->max_rate, prate), 256ULL);
+	if (max_mult < min_mult)
+		return -EINVAL;
+
+	mult = DIV_ROUND_CLOSEST_ULL(req->rate, prate);
+	mult = clamp(mult, min_mult, max_mult);
+
+	req->rate = prate * mult;
+	return 0;
+}
+
+static int cpg_pll_clk_set_rate(struct clk_hw *hw, unsigned long rate,
+				unsigned long parent_rate)
+{
+	struct cpg_pll_clk *pll_clk = to_pll_clk(hw);
+	unsigned int mult;
+	u32 val;
+
+	mult = DIV_ROUND_CLOSEST_ULL(rate, parent_rate * 2);
+	mult = clamp(mult, 1U, 256U);
+
+	if (readl(pll_clk->pllcr0_reg) & CPG_PLLxCR0_KICK)
+		return -EBUSY;
+
+	cpg_reg_modify(pll_clk->pllcr0_reg, CPG_PLLxCR0_NI,
+		       FIELD_PREP(CPG_PLLxCR0_NI, mult - 1));
+
+	/*
+	 * Set KICK bit in PLLxCR0 to update hardware setting and wait for
+	 * clock change completion.
+	 */
+	cpg_reg_modify(pll_clk->pllcr0_reg, 0, CPG_PLLxCR0_KICK);
+
+	/*
+	 * Note: There is no HW information about the worst case latency.
+	 *
+	 * Using experimental measurements, it seems that no more than
+	 * ~45 µs are needed, independently of the CPU rate.
+	 * Since this value might be dependent on external xtal rate, pll
+	 * rate or even the other emulation clocks rate, use 1000 as a
+	 * "super" safe value.
+	 */
+	return readl_poll_timeout(pll_clk->pllecr_reg, val,
+				  val & pll_clk->pllecr_pllst_mask, 0, 1000);
+}
+
+static const struct clk_ops cpg_pll_clk_ops = {
+	.recalc_rate = cpg_pll_clk_recalc_rate,
+	.determine_rate = cpg_pll_clk_determine_rate,
+	.set_rate = cpg_pll_clk_set_rate,
+};
+
+static struct clk * __init cpg_pll_clk_register(const char *name,
+						const char *parent_name,
+						void __iomem *base,
+						unsigned int cr0_offset,
+						unsigned int cr1_offset,
+						unsigned int index)
+
+{
+	struct cpg_pll_clk *pll_clk;
+	struct clk_init_data init = {};
+	struct clk *clk;
+
+	pll_clk = kzalloc(sizeof(*pll_clk), GFP_KERNEL);
+	if (!pll_clk)
+		return ERR_PTR(-ENOMEM);
+
+	init.name = name;
+	init.ops = &cpg_pll_clk_ops;
+	init.parent_names = &parent_name;
+	init.num_parents = 1;
+
+	pll_clk->hw.init = &init;
+	pll_clk->pllcr0_reg = base + cr0_offset;
+	pll_clk->pllecr_reg = base + CPG_PLLECR;
+	pll_clk->pllecr_pllst_mask = CPG_PLLECR_PLLST(index);
+
+	/* Disable Fractional Multiplication and Frequency Dithering */
+	writel(0, base + cr1_offset);
+	cpg_reg_modify(pll_clk->pllcr0_reg, CPG_PLLxCR0_SSMODE, 0);
+
+	clk = clk_register(NULL, &pll_clk->hw);
+	if (IS_ERR(clk))
+		kfree(pll_clk);
+
+	return clk;
+}
 /*
  * Z0 Clock & Z1 Clock
  */
@@ -205,6 +352,15 @@ struct clk * __init rcar_gen4_cpg_clk_register(struct device *dev,
 		div = cpg_pll_config->pll1_div;
 		break;
 
+	case CLK_TYPE_GEN4_PLL2_VAR:
+		/*
+		 * PLL2 is implemented as a custom clock, to change the
+		 * multiplier when cpufreq changes between normal and boost
+		 * modes.
+		 */
+		return cpg_pll_clk_register(core->name, __clk_get_name(parent),
+					    base, CPG_PLL2CR0, CPG_PLL2CR1, 2);
+
 	case CLK_TYPE_GEN4_PLL2:
 		mult = cpg_pll_config->pll2_mult;
 		div = cpg_pll_config->pll2_div;
diff --git a/drivers/clk/renesas/rcar-gen4-cpg.h b/drivers/clk/renesas/rcar-gen4-cpg.h
index 0a0e3bdb3a664c10..006537e29e4eb10e 100644
--- a/drivers/clk/renesas/rcar-gen4-cpg.h
+++ b/drivers/clk/renesas/rcar-gen4-cpg.h
@@ -13,6 +13,7 @@ enum rcar_gen4_clk_types {
 	CLK_TYPE_GEN4_MAIN = CLK_TYPE_CUSTOM,
 	CLK_TYPE_GEN4_PLL1,
 	CLK_TYPE_GEN4_PLL2,
+	CLK_TYPE_GEN4_PLL2_VAR,
 	CLK_TYPE_GEN4_PLL2X_3X,	/* r8a779a0 only */
 	CLK_TYPE_GEN4_PLL3,
 	CLK_TYPE_GEN4_PLL4,
-- 
2.25.1

[PATCH 2/3] clk: renesas: rcar-gen4: Add support for fractional multiplication

[Geert Uytterhoeven]

R-Car Gen4 PLLs support fractional multiplication, which can improve
accuracy when configuring a specific frequency.

Add support for fractional multiplication to the custom clock driver
for PLLs, which is currently used only for PLL2 on R-Car V4H.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
I am not so sure it is worth supporting this.
On R-Car V4H, the following clock rates are seen for PLL2 and the
Cortex-A76 CPU core clock, when using the Normal vs. the
High-Performance mode:

					Multiplication Mode
					Integer         Frational
					----------	----------
    Normal (1.7 GHz):            PLL2   3399999864      3399999997
				 Z0     1699999932      1699999999
    High-Performance (1.8 GHz):  PLL2   3599999856      3599999997
				 Z0     1799999928      1799999999

The improvement is of a similar order of magnitude as the accuracy of
the external crystal, hence insignificant...

With the current implementation, fractional multiplication does not have
any impact on lower performance points, as those rely on changing the Z0
divider (which supports 32 steps only), instead of changing the PLL.
---
 drivers/clk/renesas/rcar-gen4-cpg.c | 69 ++++++++++++++++++++++-------
 1 file changed, 54 insertions(+), 15 deletions(-)

diff --git a/drivers/clk/renesas/rcar-gen4-cpg.c b/drivers/clk/renesas/rcar-gen4-cpg.c
index c68d8b987054131b..54dc3aa82b499725 100644
--- a/drivers/clk/renesas/rcar-gen4-cpg.c
+++ b/drivers/clk/renesas/rcar-gen4-cpg.c
@@ -57,10 +57,13 @@ static u32 cpg_mode __initdata;
 #define SSMODE_DITHER		BIT(1)	/* Frequency Dithering */
 #define SSMODE_CENTER		BIT(0)	/* Center (vs. Down) Spread Dithering */
 
+#define CPG_PLLxCR1_NF		GENMASK(24, 0)	/* Fractional mult. factor */
+
 /* PLL Clocks */
 struct cpg_pll_clk {
 	struct clk_hw hw;
 	void __iomem *pllcr0_reg;
+	void __iomem *pllcr1_reg;
 	void __iomem *pllecr_reg;
 	u32 pllecr_pllst_mask;
 };
@@ -71,17 +74,26 @@ static unsigned long cpg_pll_clk_recalc_rate(struct clk_hw *hw,
 					     unsigned long parent_rate)
 {
 	struct cpg_pll_clk *pll_clk = to_pll_clk(hw);
-	unsigned int mult;
-
-	mult = FIELD_GET(CPG_PLLxCR0_NI, readl(pll_clk->pllcr0_reg)) + 1;
+	u32 cr0 = readl(pll_clk->pllcr0_reg);
+	unsigned int ni, nf;
+	unsigned long rate;
+
+	ni = (FIELD_GET(CPG_PLLxCR0_NI, cr0) + 1) * 2;
+	rate = parent_rate * ni;
+	if (cr0 & CPG_PLLxCR0_SSMODE_FM) {
+		nf = FIELD_GET(CPG_PLLxCR1_NF, readl(pll_clk->pllcr1_reg));
+		rate += ((u64)parent_rate * nf) >> 24;
+	}
 
-	return parent_rate * mult * 2;
+	return rate;
 }
 
 static int cpg_pll_clk_determine_rate(struct clk_hw *hw,
 				      struct clk_rate_request *req)
 {
-	unsigned int min_mult, max_mult, mult;
+	struct cpg_pll_clk *pll_clk = to_pll_clk(hw);
+	unsigned int min_mult, max_mult, ni, nf;
+	u32 cr0 = readl(pll_clk->pllcr0_reg);
 	unsigned long prate;
 
 	prate = req->best_parent_rate * 2;
@@ -90,10 +102,23 @@ static int cpg_pll_clk_determine_rate(struct clk_hw *hw,
 	if (max_mult < min_mult)
 		return -EINVAL;
 
-	mult = DIV_ROUND_CLOSEST_ULL(req->rate, prate);
-	mult = clamp(mult, min_mult, max_mult);
+	if (cr0 & CPG_PLLxCR0_SSMODE_FM) {
+		ni = div64_ul(req->rate, prate);
+		if (ni < min_mult) {
+			ni = min_mult;
+			nf = 0;
+		} else {
+			ni = min(ni, max_mult);
+			nf = ((u64)(req->rate - prate * ni) << 24) /
+			     req->best_parent_rate;
+		}
+	} else {
+		ni = DIV_ROUND_CLOSEST_ULL(req->rate, prate);
+		ni = clamp(ni, min_mult, max_mult);
+		nf = 0;
+	}
+	req->rate = prate * ni + (((u64)req->best_parent_rate * nf) >> 24);
 
-	req->rate = prate * mult;
 	return 0;
 }
 
@@ -101,17 +126,31 @@ static int cpg_pll_clk_set_rate(struct clk_hw *hw, unsigned long rate,
 				unsigned long parent_rate)
 {
 	struct cpg_pll_clk *pll_clk = to_pll_clk(hw);
-	unsigned int mult;
+	unsigned long prate = parent_rate * 2;
+	u32 cr0 = readl(pll_clk->pllcr0_reg);
+	unsigned int ni, nf;
+	int error;
 	u32 val;
 
-	mult = DIV_ROUND_CLOSEST_ULL(rate, parent_rate * 2);
-	mult = clamp(mult, 1U, 256U);
+	if (cr0 & CPG_PLLxCR0_SSMODE_FM) {
+		ni = div64_ul(rate, prate);
+		if (ni < 1) {
+			ni = 1;
+			nf = 0;
+		} else {
+			ni = min(ni, 256U);
+			nf = ((u64)(rate - prate * ni) << 24) / parent_rate;
+		}
+	} else {
+		ni = DIV_ROUND_CLOSEST_ULL(rate, prate);
+		ni = clamp(ni, 1U, 256U);
+	}
 
 	if (readl(pll_clk->pllcr0_reg) & CPG_PLLxCR0_KICK)
 		return -EBUSY;
 
 	cpg_reg_modify(pll_clk->pllcr0_reg, CPG_PLLxCR0_NI,
-		       FIELD_PREP(CPG_PLLxCR0_NI, mult - 1));
+		       FIELD_PREP(CPG_PLLxCR0_NI, ni - 1));
 
 	/*
 	 * Set KICK bit in PLLxCR0 to update hardware setting and wait for
@@ -161,12 +200,12 @@ static struct clk * __init cpg_pll_clk_register(const char *name,
 
 	pll_clk->hw.init = &init;
 	pll_clk->pllcr0_reg = base + cr0_offset;
+	pll_clk->pllcr1_reg = base + cr1_offset;
 	pll_clk->pllecr_reg = base + CPG_PLLECR;
 	pll_clk->pllecr_pllst_mask = CPG_PLLECR_PLLST(index);
 
-	/* Disable Fractional Multiplication and Frequency Dithering */
-	writel(0, base + cr1_offset);
-	cpg_reg_modify(pll_clk->pllcr0_reg, CPG_PLLxCR0_SSMODE, 0);
+	/* Enable Fractional Multiplication */
+	cpg_reg_modify(pll_clk->pllcr0_reg, 0, CPG_PLLxCR0_SSMODE_FM);
 
 	clk = clk_register(NULL, &pll_clk->hw);
 	if (IS_ERR(clk))
-- 
2.25.1

[PATCH 3/3] arm64: dts: renesas: r8a779g0: Add Cortex-A76 1.8 GHz opp

[Geert Uytterhoeven]

Add an operating point for running the Cortex-A76 CPU cores on R-Car
V4H at 1.8 GHz (High Performance mode).

Based on a patch in the BSP by Tho Vu.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
Tested on the Renesas White-Hawk development board by using the CPUfreq
userspace governor, enabling boost mode, writing the desired CPU clock
rate to the CPUfreq policy's "scaling_setspeed" file in sysfs, verifying
the clock rate of the Z0φ clock in debugfs, and running the dhrystones
benchmark on the various CPU cores.

$ echo 1 > /sys/devices/system/cpu/cpufreq/boost
$ echo 1800000 > /sys/devices/system/cpu/cpufreq/policy0/scaling_setspeed
---
 arch/arm64/boot/dts/renesas/r8a779g0.dtsi | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/arm64/boot/dts/renesas/r8a779g0.dtsi b/arch/arm64/boot/dts/renesas/r8a779g0.dtsi
index 83d1666a2ea16de2..7a87a5dc1b6ad219 100644
--- a/arch/arm64/boot/dts/renesas/r8a779g0.dtsi
+++ b/arch/arm64/boot/dts/renesas/r8a779g0.dtsi
@@ -39,6 +39,12 @@ opp-1700000000 {
 			clock-latency-ns = <500000>;
 			opp-suspend;
 		};
+		opp-1800000000 {
+			opp-hz = /bits/ 64 <1800000000>;
+			opp-microvolt = <880000>;
+			clock-latency-ns = <500000>;
+			turbo-mode;
+		};
 	};
 
 	cpus {
-- 
2.25.1

Re: [PATCH 2/3] clk: renesas: rcar-gen4: Add support for fractional multiplication

[Geert Uytterhoeven]

On Thu, Dec 8, 2022 at 2:07 PM Geert Uytterhoeven
<geert+renesas@glider.be> wrote:
> R-Car Gen4 PLLs support fractional multiplication, which can improve
> accuracy when configuring a specific frequency.
>
> Add support for fractional multiplication to the custom clock driver
> for PLLs, which is currently used only for PLL2 on R-Car V4H.
>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

> --- a/drivers/clk/renesas/rcar-gen4-cpg.c
> +++ b/drivers/clk/renesas/rcar-gen4-cpg.c

> @@ -101,17 +126,31 @@ static int cpg_pll_clk_set_rate(struct clk_hw *hw, unsigned long rate,
>                                 unsigned long parent_rate)
>  {
>         struct cpg_pll_clk *pll_clk = to_pll_clk(hw);
> -       unsigned int mult;
> +       unsigned long prate = parent_rate * 2;
> +       u32 cr0 = readl(pll_clk->pllcr0_reg);
> +       unsigned int ni, nf;
> +       int error;

"error" is unused, and should be dropped.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH 2/3] clk: renesas: rcar-gen4: Add support for fractional multiplication

[Geert Uytterhoeven]

On Thu, Dec 8, 2022 at 2:07 PM Geert Uytterhoeven
<geert+renesas@glider.be> wrote:
> R-Car Gen4 PLLs support fractional multiplication, which can improve
> accuracy when configuring a specific frequency.
>
> Add support for fractional multiplication to the custom clock driver
> for PLLs, which is currently used only for PLL2 on R-Car V4H.
>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> ---
> I am not so sure it is worth supporting this.
> On R-Car V4H, the following clock rates are seen for PLL2 and the
> Cortex-A76 CPU core clock, when using the Normal vs. the
> High-Performance mode:
>
>                                         Multiplication Mode
>                                         Integer         Frational
>                                         ----------      ----------
>     Normal (1.7 GHz):            PLL2   3399999864      3399999997
>                                  Z0     1699999932      1699999999
>     High-Performance (1.8 GHz):  PLL2   3599999856      3599999997
>                                  Z0     1799999928      1799999999
>
> The improvement is of a similar order of magnitude as the accuracy of
> the external crystal, hence insignificant...

Hence I'm ignoring this, unless someone has a good reason to push
through...

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds