[v3,4/5] clk: Hi6220: add stub clock driver

Message ID 1438564418-15948-5-git-send-email-leo.yan@linaro.org
State New
Headers show

Commit Message

Leo Yan Aug. 3, 2015, 1:13 a.m.
On Hi6220, there have some clocks which can use mailbox channel to send
messages to power controller to change frequency; this includes CPU, GPU
and DDR clocks.

For dynamic frequency scaling, firstly need write the frequency value to
SRAM region, and then send message to mailbox to trigger power controller
to handle this requirement. This driver will use syscon APIs to pass SRAM
memory region and use common mailbox APIs for channels accessing.

This init driver will support cpu frequency change firstly.

Signed-off-by: Leo Yan <leo.yan@linaro.org>
---
 drivers/clk/hisilicon/Kconfig           |   2 +-
 drivers/clk/hisilicon/Makefile          |   2 +-
 drivers/clk/hisilicon/clk-hi6220-stub.c | 279 ++++++++++++++++++++++++++++++++
 3 files changed, 281 insertions(+), 2 deletions(-)
 create mode 100644 drivers/clk/hisilicon/clk-hi6220-stub.c

Comments

Leo Yan Aug. 4, 2015, 6:27 a.m. | #1
Hi Stephen,

On Mon, Aug 03, 2015 at 02:37:52PM -0700, Stephen Boyd wrote:
> On 08/03, Leo Yan wrote:
> > diff --git a/drivers/clk/hisilicon/clk-hi6220-stub.c b/drivers/clk/hisilicon/clk-hi6220-stub.c
> > new file mode 100644
> > index 0000000..0931666
> > --- /dev/null
> > +++ b/drivers/clk/hisilicon/clk-hi6220-stub.c
> > @@ -0,0 +1,279 @@
> > +/*
> > + * Hi6220 stub clock driver
> > + *
> > + * Copyright (c) 2015 Hisilicon Limited.
> > + * Copyright (c) 2015 Linaro Limited.
> > + *
> > + * Author: Leo Yan <leo.yan@linaro.org>
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2 as
> > + * published by the Free Software Foundation.
> > + *
> > + */
> > +
> > +#include <linux/clkdev.h>
> 
> Is this include used?
> 
> > +#include <linux/clk-provider.h>
> > +#include <linux/clk.h>
> 
> Is this include used?
> 
> > +#include <linux/err.h>
> > +#include <linux/mfd/syscon.h>
> > +#include <linux/mailbox_client.h>
> > +#include <linux/of.h>
> > +#include <linux/of_device.h>
> > +#include <linux/regmap.h>
> > +#include <linux/slab.h>
> > +#include <linux/kernel.h>
> > +
> > +#include <dt-bindings/clock/hi6220-clock.h>
> > +
> > +/* Stub clocks id */
> > +#define HI6220_STUB_ACPU0		0
> > +#define HI6220_STUB_ACPU1		1
> > +#define HI6220_STUB_GPU			2
> > +#define HI6220_STUB_DDR			5
> > +
> > +/* Mailbox message */
> > +#define HI6220_MBOX_MSG_LEN		8
> > +
> > +#define HI6220_MBOX_FREQ		(0xA)
> > +#define HI6220_MBOX_CMD_SET		(0x3)
> > +#define HI6220_MBOX_OBJ_AP		(0x0)
> > +
> > +/* CPU dynamic frequency scaling */
> > +#define ACPU_DFS_FREQ_MAX		(0x1724)
> > +#define ACPU_DFS_CUR_FREQ		(0x17CC)
> > +#define ACPU_DFS_FLAG			(0x1B30)
> > +#define ACPU_DFS_FREQ_REQ		(0x1B34)
> > +#define ACPU_DFS_FREQ_LMT		(0x1B38)
> > +#define ACPU_DFS_LOCK_FLAG		(0xAEAEAEAE)
> 
> We don't need parenthesis around single values in these macros.
> 
> > +
> > +#define to_stub_clk(hw) container_of(hw, struct hi6220_stub_clk, hw)
> > +
> > +struct hi6220_stub_clk {
> > +	u32 id;
> > +	u32 rate;
> > +
> > +	struct device *dev;
> > +	struct clk_hw hw;
> > +
> > +	struct regmap *dfs_map;
> > +	struct mbox_client cl;
> > +	struct mbox_chan *mbox;
> > +};
> > +
> > +struct hi6220_mbox_msg {
> > +	unsigned char type;
> > +	unsigned char cmd;
> > +	unsigned char obj;
> > +	unsigned char src;
> > +	unsigned char para[4];
> > +};
> > +
> > +union hi6220_mbox_data {
> > +	unsigned int data[HI6220_MBOX_MSG_LEN];
> > +	struct hi6220_mbox_msg msg;
> > +};
> > +
> > +static unsigned int hi6220_acpu_get_freq(struct hi6220_stub_clk *stub_clk)
> > +{
> > +	unsigned int freq;
> > +
> > +	regmap_read(stub_clk->dfs_map, ACPU_DFS_CUR_FREQ, &freq);
> > +	return freq;
> > +}
> > +
> > +static int hi6220_acpu_set_freq(struct hi6220_stub_clk *stub_clk,
> > +				unsigned int freq)
> > +{
> > +	union hi6220_mbox_data data;
> > +
> > +	stub_clk->mbox = mbox_request_channel(&stub_clk->cl, 0);
> 
> Why not request the channel once in probe?
> 
> > +	if (IS_ERR(stub_clk->mbox)) {
> > +		dev_err(stub_clk->dev, "failed get mailbox channel\n");
> > +		return PTR_ERR(stub_clk->mbox);
> > +	};
> > +
> > +	/* set the frequency in sram */
> > +	regmap_write(stub_clk->dfs_map, ACPU_DFS_FREQ_REQ, freq);
> > +
> > +	/* compound mailbox message */
> > +	data.msg.type = HI6220_MBOX_FREQ;
> > +	data.msg.cmd  = HI6220_MBOX_CMD_SET;
> > +	data.msg.obj  = HI6220_MBOX_OBJ_AP;
> > +	data.msg.src  = HI6220_MBOX_OBJ_AP;
> > +
> > +	mbox_send_message(stub_clk->mbox, &data);
> > +	mbox_free_channel(stub_clk->mbox);
> > +	return 0;
> > +}
> > +
> > +static int hi6220_acpu_round_freq(struct hi6220_stub_clk *stub_clk,
> > +				  unsigned int freq)
> > +{
> > +	unsigned int limit_flag, limit_freq = UINT_MAX;
> > +	unsigned int max_freq;
> > +
> > +	/* check the constrainted frequency */
> 
> s/constrainted/constrained/ ?
> 
> > +	regmap_read(stub_clk->dfs_map, ACPU_DFS_FLAG, &limit_flag);
> > +	if (limit_flag == ACPU_DFS_LOCK_FLAG)
> > +		regmap_read(stub_clk->dfs_map, ACPU_DFS_FREQ_LMT, &limit_freq);
> > +
> > +	/* check the supported maximum frequency */
> > +	regmap_read(stub_clk->dfs_map, ACPU_DFS_FREQ_MAX, &max_freq);
> > +
> > +	/* calculate the real maximum frequency */
> > +	max_freq = min(max_freq, limit_freq);
> > +
> > +	if (WARN_ON(freq > max_freq))
> > +		freq = max_freq;
> > +
> > +	return freq;
> > +}
> > +
> > +static unsigned long hi6220_stub_clk_recalc_rate(struct clk_hw *hw,
> > +		unsigned long parent_rate)
> > +{
> > +	u32 rate = 0;
> > +	struct hi6220_stub_clk *stub_clk = to_stub_clk(hw);
> > +
> > +	switch (stub_clk->id) {
> > +	case HI6220_STUB_ACPU0:
> > +		rate = hi6220_acpu_get_freq(stub_clk);
> > +
> > +		/* convert from KHz to Hz */
> 
> s/KHz/kHz/ ?
> 
> > +		rate *= 1000;
> > +		break;
> > +
> > +	default:
> > +		dev_err(stub_clk->dev, "%s: un-supported clock id %d\n",
> > +			__func__, stub_clk->id);
> > +		break;
> > +	}
> > +
> > +	return rate;
> > +}
> > +
> > +static int hi6220_stub_clk_set_rate(struct clk_hw *hw, unsigned long rate,
> > +                    unsigned long parent_rate)
> > +{
> > +	struct hi6220_stub_clk *stub_clk = to_stub_clk(hw);
> > +	unsigned long new_rate = rate / 1000;  /* Khz */
> 
> s/KHz/kHz/ ?
> 
> > +	int ret = 0;
> > +
> > +	switch (stub_clk->id) {
> > +	case HI6220_STUB_ACPU0:
> > +		ret = hi6220_acpu_set_freq(stub_clk, new_rate);
> > +		if (ret < 0)
> > +			return ret;
> > +
> > +		break;
> > +
> > +	default:
> > +		dev_err(stub_clk->dev, "%s: un-supported clock id %d\n",
> > +			__func__, stub_clk->id);
> > +		break;
> > +	}
> > +
> > +	stub_clk->rate = new_rate;
> 
> Why do we store away the rate? Is this used anywhere?
> 
> > +
> > +	pr_debug("%s: set rate=%ldKhz\n", __func__, new_rate);
> > +	return ret;
> > +}
> > +
> > +static long hi6220_stub_clk_round_rate(struct clk_hw *hw, unsigned long rate,
> > +		unsigned long *parent_rate)
> > +{
> > +	struct hi6220_stub_clk *stub_clk = to_stub_clk(hw);
> > +	unsigned long new_rate = rate / 1000;  /* Khz */
> 
> s/KHz/kHz/ ?
> 
> > +
> > +	switch (stub_clk->id) {
> > +	case HI6220_STUB_ACPU0:
> > +		new_rate = hi6220_acpu_round_freq(stub_clk, new_rate);
> > +
> > +		/* convert from KHz to Hz */
> 
> s/KHz/kHz/ ?
> 
> > +		new_rate *= 1000;
> > +		break;
> > +
> > +	default:
> > +		dev_err(stub_clk->dev, "%s: un-supported clock id %d\n",
> > +			__func__, stub_clk->id);
> > +		break;
> > +	}
> > +
> > +	return new_rate;
> > +}
> > +
> > +static struct clk_ops hi6220_stub_clk_ops = {
> 
> const?
> 
> > +	.recalc_rate	= hi6220_stub_clk_recalc_rate,
> > +	.round_rate	= hi6220_stub_clk_round_rate,
> > +	.set_rate	= hi6220_stub_clk_set_rate,
> > +};
> > +
> > +static int hi6220_stub_clk_probe(struct platform_device *pdev)
> > +{
> > +	struct device *dev = &pdev->dev;
> > +	struct clk_init_data init;
> > +	struct hi6220_stub_clk *stub_clk;
> > +	struct clk *clk;
> > +	struct device_node *np = pdev->dev.of_node;
> > +
> > +	stub_clk = devm_kzalloc(&pdev->dev, sizeof(*stub_clk), GFP_KERNEL);
> 
> just use dev?
> 
> > +	if (!stub_clk)
> > +		return -ENOMEM;
> > +
> > +	stub_clk->dfs_map = syscon_regmap_lookup_by_phandle(np,
> > +				"hisilicon,hi6220-clk-sram");
> > +	if (IS_ERR(stub_clk->dfs_map)) {
> > +		dev_err(dev, "failed to get sram regmap\n");
> > +		return PTR_ERR(stub_clk->dfs_map);
> > +	}
> > +
> > +	stub_clk->hw.init = &init;
> > +	stub_clk->dev = dev;
> > +	stub_clk->id = HI6220_STUB_ACPU0;
> > +
> > +	/* Use mailbox client with blocking mode */
> > +	stub_clk->cl.dev = &pdev->dev;
> 
> just use dev?
> 
> > +	stub_clk->cl.tx_done = NULL;
> > +	stub_clk->cl.tx_block = true;
> > +	stub_clk->cl.tx_tout = 500;
> > +	stub_clk->cl.knows_txdone = false;
> > +
> > +	init.name = "acpu0";
> > +	init.ops = &hi6220_stub_clk_ops;
> > +	init.num_parents = 0;
> > +	init.flags = CLK_IS_ROOT;
> > +
> > +	clk = clk_register(NULL, &stub_clk->hw);
> 
> why not devm_clk_register?
> 
> > +	if (IS_ERR(clk))
> > +		return PTR_ERR(clk);
> > +
> > +	of_clk_add_provider(pdev->dev.of_node, of_clk_src_simple_get, clk);
> 
> And check this for an error return value? Also, just use dev?
> 
> > +
> > +	/* initialize buffer to zero */
> > +	regmap_write(stub_clk->dfs_map, ACPU_DFS_FLAG, 0x0);
> > +	regmap_write(stub_clk->dfs_map, ACPU_DFS_FREQ_REQ, 0x0);
> > +	regmap_write(stub_clk->dfs_map, ACPU_DFS_FREQ_LMT, 0x0);
> > +
> > +	dev_dbg(&pdev->dev, "Registered clock '%s'\n", init.name);
> 
> just use dev?
> 
> > +	return 0;
> > +}
> > +
> > +static const struct of_device_id hi6220_stub_clk_of_match[] = {
> > +	{ .compatible = "hisilicon,hi6220-stub-clk", },
> > +	{}
> > +};
> > +
> > +static struct platform_driver hi6220_stub_clk_driver = {
> > +	.driver	= {
> > +		.name = "hi6220-stub-clk",
> > +		.of_match_table = of_match_ptr(hi6220_stub_clk_of_match),
> 
> We can leave off of_match_ptr() here.
> 
> > +	},
> > +	.probe = hi6220_stub_clk_probe,
> > +};


Thanks for review; Accept all comments and will refine for them :)

Thanks,
Leo Yan
--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Kevin Hilman Sept. 2, 2015, 12:28 a.m. | #2
On Sun, Aug 2, 2015 at 6:13 PM, Leo Yan <leo.yan@linaro.org> wrote:
> On Hi6220, there have some clocks which can use mailbox channel to send
> messages to power controller to change frequency; this includes CPU, GPU
> and DDR clocks.
>
> For dynamic frequency scaling, firstly need write the frequency value to
> SRAM region, and then send message to mailbox to trigger power controller
> to handle this requirement. This driver will use syscon APIs to pass SRAM
> memory region and use common mailbox APIs for channels accessing.
>
> This init driver will support cpu frequency change firstly.
>
> Signed-off-by: Leo Yan <leo.yan@linaro.org>

The kernelci.org build/boot bot detected boot failures in
linux-next[1], and the failure was bisected down to this patch (landed
in linux-next as commit c1628a2c416da947f5afac615d53189250fa49cb.

I verifed that reverting this commit on top of next-20150901 gets the
hikey booting again.

Kevin

[1] http://kernelci.org/boot/hi6220-hikey/
--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Leo Yan Sept. 2, 2015, 1:52 a.m. | #3
Hi Kevin,

On Tue, Sep 01, 2015 at 05:28:03PM -0700, Kevin Hilman wrote:
> On Sun, Aug 2, 2015 at 6:13 PM, Leo Yan <leo.yan@linaro.org> wrote:
> > On Hi6220, there have some clocks which can use mailbox channel to send
> > messages to power controller to change frequency; this includes CPU, GPU
> > and DDR clocks.
> >
> > For dynamic frequency scaling, firstly need write the frequency value to
> > SRAM region, and then send message to mailbox to trigger power controller
> > to handle this requirement. This driver will use syscon APIs to pass SRAM
> > memory region and use common mailbox APIs for channels accessing.
> >
> > This init driver will support cpu frequency change firstly.
> >
> > Signed-off-by: Leo Yan <leo.yan@linaro.org>
> 
> The kernelci.org build/boot bot detected boot failures in
> linux-next[1], and the failure was bisected down to this patch (landed
> in linux-next as commit c1628a2c416da947f5afac615d53189250fa49cb.
> 
> I verifed that reverting this commit on top of next-20150901 gets the
> hikey booting again.

Thanks for reporting. This issue has been confirmed at my side, it's
caused by the patch have added dependency with MAILBOX, will fix this
issue and send patch.

Thanks,
Leo Yan
--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Patch

diff --git a/drivers/clk/hisilicon/Kconfig b/drivers/clk/hisilicon/Kconfig
index b4165ba..2c16807 100644
--- a/drivers/clk/hisilicon/Kconfig
+++ b/drivers/clk/hisilicon/Kconfig
@@ -1,6 +1,6 @@ 
 config COMMON_CLK_HI6220
 	bool "Hi6220 Clock Driver"
-	depends on ARCH_HISI || COMPILE_TEST
+	depends on (ARCH_HISI || COMPILE_TEST) && MAILBOX
 	default ARCH_HISI
 	help
 	  Build the Hisilicon Hi6220 clock driver based on the common clock framework.
diff --git a/drivers/clk/hisilicon/Makefile b/drivers/clk/hisilicon/Makefile
index 48f0116..4a1001a 100644
--- a/drivers/clk/hisilicon/Makefile
+++ b/drivers/clk/hisilicon/Makefile
@@ -7,4 +7,4 @@  obj-y	+= clk.o clkgate-separated.o clkdivider-hi6220.o
 obj-$(CONFIG_ARCH_HI3xxx)	+= clk-hi3620.o
 obj-$(CONFIG_ARCH_HIP04)	+= clk-hip04.o
 obj-$(CONFIG_ARCH_HIX5HD2)	+= clk-hix5hd2.o
-obj-$(CONFIG_COMMON_CLK_HI6220)	+= clk-hi6220.o
+obj-$(CONFIG_COMMON_CLK_HI6220)	+= clk-hi6220.o clk-hi6220-stub.o
diff --git a/drivers/clk/hisilicon/clk-hi6220-stub.c b/drivers/clk/hisilicon/clk-hi6220-stub.c
new file mode 100644
index 0000000..0931666
--- /dev/null
+++ b/drivers/clk/hisilicon/clk-hi6220-stub.c
@@ -0,0 +1,279 @@ 
+/*
+ * Hi6220 stub clock driver
+ *
+ * Copyright (c) 2015 Hisilicon Limited.
+ * Copyright (c) 2015 Linaro Limited.
+ *
+ * Author: Leo Yan <leo.yan@linaro.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#include <linux/clkdev.h>
+#include <linux/clk-provider.h>
+#include <linux/clk.h>
+#include <linux/err.h>
+#include <linux/mfd/syscon.h>
+#include <linux/mailbox_client.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/regmap.h>
+#include <linux/slab.h>
+#include <linux/kernel.h>
+
+#include <dt-bindings/clock/hi6220-clock.h>
+
+/* Stub clocks id */
+#define HI6220_STUB_ACPU0		0
+#define HI6220_STUB_ACPU1		1
+#define HI6220_STUB_GPU			2
+#define HI6220_STUB_DDR			5
+
+/* Mailbox message */
+#define HI6220_MBOX_MSG_LEN		8
+
+#define HI6220_MBOX_FREQ		(0xA)
+#define HI6220_MBOX_CMD_SET		(0x3)
+#define HI6220_MBOX_OBJ_AP		(0x0)
+
+/* CPU dynamic frequency scaling */
+#define ACPU_DFS_FREQ_MAX		(0x1724)
+#define ACPU_DFS_CUR_FREQ		(0x17CC)
+#define ACPU_DFS_FLAG			(0x1B30)
+#define ACPU_DFS_FREQ_REQ		(0x1B34)
+#define ACPU_DFS_FREQ_LMT		(0x1B38)
+#define ACPU_DFS_LOCK_FLAG		(0xAEAEAEAE)
+
+#define to_stub_clk(hw) container_of(hw, struct hi6220_stub_clk, hw)
+
+struct hi6220_stub_clk {
+	u32 id;
+	u32 rate;
+
+	struct device *dev;
+	struct clk_hw hw;
+
+	struct regmap *dfs_map;
+	struct mbox_client cl;
+	struct mbox_chan *mbox;
+};
+
+struct hi6220_mbox_msg {
+	unsigned char type;
+	unsigned char cmd;
+	unsigned char obj;
+	unsigned char src;
+	unsigned char para[4];
+};
+
+union hi6220_mbox_data {
+	unsigned int data[HI6220_MBOX_MSG_LEN];
+	struct hi6220_mbox_msg msg;
+};
+
+static unsigned int hi6220_acpu_get_freq(struct hi6220_stub_clk *stub_clk)
+{
+	unsigned int freq;
+
+	regmap_read(stub_clk->dfs_map, ACPU_DFS_CUR_FREQ, &freq);
+	return freq;
+}
+
+static int hi6220_acpu_set_freq(struct hi6220_stub_clk *stub_clk,
+				unsigned int freq)
+{
+	union hi6220_mbox_data data;
+
+	stub_clk->mbox = mbox_request_channel(&stub_clk->cl, 0);
+	if (IS_ERR(stub_clk->mbox)) {
+		dev_err(stub_clk->dev, "failed get mailbox channel\n");
+		return PTR_ERR(stub_clk->mbox);
+	};
+
+	/* set the frequency in sram */
+	regmap_write(stub_clk->dfs_map, ACPU_DFS_FREQ_REQ, freq);
+
+	/* compound mailbox message */
+	data.msg.type = HI6220_MBOX_FREQ;
+	data.msg.cmd  = HI6220_MBOX_CMD_SET;
+	data.msg.obj  = HI6220_MBOX_OBJ_AP;
+	data.msg.src  = HI6220_MBOX_OBJ_AP;
+
+	mbox_send_message(stub_clk->mbox, &data);
+	mbox_free_channel(stub_clk->mbox);
+	return 0;
+}
+
+static int hi6220_acpu_round_freq(struct hi6220_stub_clk *stub_clk,
+				  unsigned int freq)
+{
+	unsigned int limit_flag, limit_freq = UINT_MAX;
+	unsigned int max_freq;
+
+	/* check the constrainted frequency */
+	regmap_read(stub_clk->dfs_map, ACPU_DFS_FLAG, &limit_flag);
+	if (limit_flag == ACPU_DFS_LOCK_FLAG)
+		regmap_read(stub_clk->dfs_map, ACPU_DFS_FREQ_LMT, &limit_freq);
+
+	/* check the supported maximum frequency */
+	regmap_read(stub_clk->dfs_map, ACPU_DFS_FREQ_MAX, &max_freq);
+
+	/* calculate the real maximum frequency */
+	max_freq = min(max_freq, limit_freq);
+
+	if (WARN_ON(freq > max_freq))
+		freq = max_freq;
+
+	return freq;
+}
+
+static unsigned long hi6220_stub_clk_recalc_rate(struct clk_hw *hw,
+		unsigned long parent_rate)
+{
+	u32 rate = 0;
+	struct hi6220_stub_clk *stub_clk = to_stub_clk(hw);
+
+	switch (stub_clk->id) {
+	case HI6220_STUB_ACPU0:
+		rate = hi6220_acpu_get_freq(stub_clk);
+
+		/* convert from KHz to Hz */
+		rate *= 1000;
+		break;
+
+	default:
+		dev_err(stub_clk->dev, "%s: un-supported clock id %d\n",
+			__func__, stub_clk->id);
+		break;
+	}
+
+	return rate;
+}
+
+static int hi6220_stub_clk_set_rate(struct clk_hw *hw, unsigned long rate,
+                    unsigned long parent_rate)
+{
+	struct hi6220_stub_clk *stub_clk = to_stub_clk(hw);
+	unsigned long new_rate = rate / 1000;  /* Khz */
+	int ret = 0;
+
+	switch (stub_clk->id) {
+	case HI6220_STUB_ACPU0:
+		ret = hi6220_acpu_set_freq(stub_clk, new_rate);
+		if (ret < 0)
+			return ret;
+
+		break;
+
+	default:
+		dev_err(stub_clk->dev, "%s: un-supported clock id %d\n",
+			__func__, stub_clk->id);
+		break;
+	}
+
+	stub_clk->rate = new_rate;
+
+	pr_debug("%s: set rate=%ldKhz\n", __func__, new_rate);
+	return ret;
+}
+
+static long hi6220_stub_clk_round_rate(struct clk_hw *hw, unsigned long rate,
+		unsigned long *parent_rate)
+{
+	struct hi6220_stub_clk *stub_clk = to_stub_clk(hw);
+	unsigned long new_rate = rate / 1000;  /* Khz */
+
+	switch (stub_clk->id) {
+	case HI6220_STUB_ACPU0:
+		new_rate = hi6220_acpu_round_freq(stub_clk, new_rate);
+
+		/* convert from KHz to Hz */
+		new_rate *= 1000;
+		break;
+
+	default:
+		dev_err(stub_clk->dev, "%s: un-supported clock id %d\n",
+			__func__, stub_clk->id);
+		break;
+	}
+
+	return new_rate;
+}
+
+static struct clk_ops hi6220_stub_clk_ops = {
+	.recalc_rate	= hi6220_stub_clk_recalc_rate,
+	.round_rate	= hi6220_stub_clk_round_rate,
+	.set_rate	= hi6220_stub_clk_set_rate,
+};
+
+static int hi6220_stub_clk_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct clk_init_data init;
+	struct hi6220_stub_clk *stub_clk;
+	struct clk *clk;
+	struct device_node *np = pdev->dev.of_node;
+
+	stub_clk = devm_kzalloc(&pdev->dev, sizeof(*stub_clk), GFP_KERNEL);
+	if (!stub_clk)
+		return -ENOMEM;
+
+	stub_clk->dfs_map = syscon_regmap_lookup_by_phandle(np,
+				"hisilicon,hi6220-clk-sram");
+	if (IS_ERR(stub_clk->dfs_map)) {
+		dev_err(dev, "failed to get sram regmap\n");
+		return PTR_ERR(stub_clk->dfs_map);
+	}
+
+	stub_clk->hw.init = &init;
+	stub_clk->dev = dev;
+	stub_clk->id = HI6220_STUB_ACPU0;
+
+	/* Use mailbox client with blocking mode */
+	stub_clk->cl.dev = &pdev->dev;
+	stub_clk->cl.tx_done = NULL;
+	stub_clk->cl.tx_block = true;
+	stub_clk->cl.tx_tout = 500;
+	stub_clk->cl.knows_txdone = false;
+
+	init.name = "acpu0";
+	init.ops = &hi6220_stub_clk_ops;
+	init.num_parents = 0;
+	init.flags = CLK_IS_ROOT;
+
+	clk = clk_register(NULL, &stub_clk->hw);
+	if (IS_ERR(clk))
+		return PTR_ERR(clk);
+
+	of_clk_add_provider(pdev->dev.of_node, of_clk_src_simple_get, clk);
+
+	/* initialize buffer to zero */
+	regmap_write(stub_clk->dfs_map, ACPU_DFS_FLAG, 0x0);
+	regmap_write(stub_clk->dfs_map, ACPU_DFS_FREQ_REQ, 0x0);
+	regmap_write(stub_clk->dfs_map, ACPU_DFS_FREQ_LMT, 0x0);
+
+	dev_dbg(&pdev->dev, "Registered clock '%s'\n", init.name);
+	return 0;
+}
+
+static const struct of_device_id hi6220_stub_clk_of_match[] = {
+	{ .compatible = "hisilicon,hi6220-stub-clk", },
+	{}
+};
+
+static struct platform_driver hi6220_stub_clk_driver = {
+	.driver	= {
+		.name = "hi6220-stub-clk",
+		.of_match_table = of_match_ptr(hi6220_stub_clk_of_match),
+	},
+	.probe = hi6220_stub_clk_probe,
+};
+
+static int __init hi6220_stub_clk_init(void)
+{
+	return platform_driver_register(&hi6220_stub_clk_driver);
+}
+core_initcall(hi6220_stub_clk_init);