[PATCH v3 1/1][Resend] misc: sram: add dev_pm_ops to support module power gate

[PATCH v3 1/1][Resend] misc: sram: add dev_pm_ops to support module power gate

[Shenwei Wang]

When system goes into low power states like SUSPEND_MEM and
HIBERNATION, the hardware IP block may be powered off to reduce
the power consumption. This power down will lost all the
data inside the ram. This patch added the dev_pm_ops and
implemented two callbacks: suspend_noirq and resume_noirq, which
will save the data in the on-chip-ram right before power down
and restore it after system resumes.

A new property string named "can-power-gate" is added to
the devicetree bindings too.

Based-on-a-patch-by: Anson Huang <b20788@freescale.com>
Signed-off-by: Shenwei Wang <shenwei.wang@freescale.com>

---
Change log:

PATCH v3
	Removed the unnecessary clk_enable/clk_disable.

PATCH v2
	Use vmalloc to allocate the SRAM backup memory.
	Code clean up.

 Documentation/devicetree/bindings/misc/sram.txt |  2 ++
 drivers/misc/sram.c                             | 42 +++++++++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/Documentation/devicetree/bindings/misc/sram.txt b/Documentation/devicetree/bindings/misc/sram.txt
index 36cbe5a..1170086 100644
--- a/Documentation/devicetree/bindings/misc/sram.txt
+++ b/Documentation/devicetree/bindings/misc/sram.txt
@@ -33,6 +33,8 @@ Optional properties in the area nodes:

 - compatible : standard definition, should contain a vendor specific string
                in the form <vendor>,[<device>-]<usage>
+- can-power-gate: a property to tell the driver that the sram can support
+		power gate

 Example:

diff --git a/drivers/misc/sram.c b/drivers/misc/sram.c
index 15c33cc..db9f1fa 100644
--- a/drivers/misc/sram.c
+++ b/drivers/misc/sram.c
@@ -30,7 +30,9 @@

 struct sram_dev {
 	struct device *dev;
+	void *power_off_save;
 	void __iomem *virt_base;
+	u32 size;

 	struct gen_pool *pool;
 	struct clk *clk;
@@ -156,6 +158,33 @@ static int sram_reserve_regions(struct sram_dev *sram, struct resource *res)
 	return ret;
 }

+static int sram_suspend_noirq(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct sram_dev *sram = platform_get_drvdata(pdev);
+
+	if (!sram->power_off_save)
+		return 0;
+
+	/* Save necessary regs */
+	memcpy(sram->power_off_save, sram->virt_base, sram->size);
+
+	return 0;
+}
+
+static int sram_resume_noirq(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct sram_dev *sram = platform_get_drvdata(pdev);
+
+	if (!sram->power_off_save)
+		return 0;
+
+	memcpy(sram->virt_base, sram->power_off_save, sram->size);
+
+	return 0;
+}
+
 static int sram_probe(struct platform_device *pdev)
 {
 	struct sram_dev *sram;
@@ -176,6 +205,7 @@ static int sram_probe(struct platform_device *pdev)
 	}

 	size = resource_size(res);
+	sram->size = size;

 	if (!devm_request_mem_region(sram->dev, res->start, size, pdev->name)) {
 		dev_err(sram->dev, "could not request region for resource\n");
@@ -203,6 +233,9 @@ static int sram_probe(struct platform_device *pdev)

 	platform_set_drvdata(pdev, sram);

+	if (of_property_read_bool(pdev->dev.of_node, "can-power-gate"))
+		sram->power_off_save = vmalloc(size);
+
 	dev_dbg(sram->dev, "SRAM pool: %zu KiB @ 0x%p\n",
 		gen_pool_size(sram->pool) / 1024, sram->virt_base);

@@ -219,6 +252,9 @@ static int sram_remove(struct platform_device *pdev)
 	if (sram->clk)
 		clk_disable_unprepare(sram->clk);

+	if (sram->power_off_save)
+		vfree(sram->power_off_save);
+
 	return 0;
 }

@@ -229,10 +265,16 @@ static const struct of_device_id sram_dt_ids[] = {
 };
 #endif

+static const struct dev_pm_ops sram_pm_ops = {
+	.suspend_noirq = sram_suspend_noirq,
+	.resume_noirq = sram_resume_noirq,
+};
+
 static struct platform_driver sram_driver = {
 	.driver = {
 		.name = "sram",
 		.of_match_table = of_match_ptr(sram_dt_ids),
+		.pm	= &sram_pm_ops,
 	},
 	.probe = sram_probe,
 	.remove = sram_remove,
--
2.5.0.rc2

Re: [PATCH v3 1/1][Resend] misc: sram: add dev_pm_ops to support module power gate

[Sudeep Holla]

On 25/08/15 23:03, Shenwei Wang wrote:
> When system goes into low power states like SUSPEND_MEM and
> HIBERNATION, the hardware IP block may be powered off to reduce
> the power consumption. This power down will lost all the
> data inside the ram. This patch added the dev_pm_ops and
> implemented two callbacks: suspend_noirq and resume_noirq, which
> will save the data in the on-chip-ram right before power down
> and restore it after system resumes.
>
> A new property string named "can-power-gate" is added to
> the devicetree bindings too.
>
> Based-on-a-patch-by: Anson Huang <b20788-KZfg59tc24xl57MIdRCFDg@public.gmane.org>
> Signed-off-by: Shenwei Wang <shenwei.wang-KZfg59tc24xl57MIdRCFDg@public.gmane.org>
>
> ---
> Change log:
>
> PATCH v3
> 	Removed the unnecessary clk_enable/clk_disable.
>
> PATCH v2
> 	Use vmalloc to allocate the SRAM backup memory.
> 	Code clean up.
>
>   Documentation/devicetree/bindings/misc/sram.txt |  2 ++
>   drivers/misc/sram.c                             | 42 +++++++++++++++++++++++++
>   2 files changed, 44 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/misc/sram.txt b/Documentation/devicetree/bindings/misc/sram.txt
> index 36cbe5a..1170086 100644
> --- a/Documentation/devicetree/bindings/misc/sram.txt
> +++ b/Documentation/devicetree/bindings/misc/sram.txt
> @@ -33,6 +33,8 @@ Optional properties in the area nodes:
>
>   - compatible : standard definition, should contain a vendor specific string
>                  in the form <vendor>,[<device>-]<usage>
> +- can-power-gate: a property to tell the driver that the sram can support
> +		power gate
>
>   Example:
>
> diff --git a/drivers/misc/sram.c b/drivers/misc/sram.c
> index 15c33cc..db9f1fa 100644
> --- a/drivers/misc/sram.c
> +++ b/drivers/misc/sram.c
> @@ -30,7 +30,9 @@
>
>   struct sram_dev {
>   	struct device *dev;
> +	void *power_off_save;
>   	void __iomem *virt_base;
> +	u32 size;
>
>   	struct gen_pool *pool;
>   	struct clk *clk;
> @@ -156,6 +158,33 @@ static int sram_reserve_regions(struct sram_dev *sram, struct resource *res)
>   	return ret;
>   }
>
> +static int sram_suspend_noirq(struct device *dev)
> +{
> +	struct platform_device *pdev = to_platform_device(dev);
> +	struct sram_dev *sram = platform_get_drvdata(pdev);
> +
> +	if (!sram->power_off_save)
> +		return 0;
> +
> +	/* Save necessary regs */
> +	memcpy(sram->power_off_save, sram->virt_base, sram->size);
> +
> +	return 0;
> +}
> +
> +static int sram_resume_noirq(struct device *dev)
> +{
> +	struct platform_device *pdev = to_platform_device(dev);
> +	struct sram_dev *sram = platform_get_drvdata(pdev);
> +
> +	if (!sram->power_off_save)
> +		return 0;
> +
> +	memcpy(sram->virt_base, sram->power_off_save, sram->size);

As I objected in the original thread[1], I am just iterating myself here
again. IMO this is unnecessary and can be avoided. It's also not
scalable for large SRAM. I *still can't understand* what's the use-case
where you need to save/restore the entire SRAM content.

I see it's mostly used for audio/video and some crypto use-case(in the
mainline). In most of those cases, when you enter S2R, all the devices
*needs to be in quiescent state* which implies they no longer use SRAM.
So can you please care to provide your reasons for this save/restore ?

On some platforms, it's used for PM in which case it needs to be always on.

Regards,
Sudeep

[1] http://www.spinics.net/lists/arm-kernel/msg441449.html
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