[2/5] nvmem: mtk-efuse: use stack for nvmem_config instead of malloc'ing it

Message ID 1505134864-11975-3-git-send-email-yamada.masahiro@socionext.com
State Superseded
Headers show
Series
  • nvmem: some cleanups and sparse warning fixes
Related show

Commit Message

Masahiro Yamada Sept. 11, 2017, 1:01 p.m.
nvmem_register() copies all the members of nvmem_config to
nvmem_device.  So, nvmem_config is one-time use data during
probing.  There is no point to keep it until the driver detach.
Using stack should be no problem because nvmem_config is pretty
small.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

---

 drivers/nvmem/mtk-efuse.c | 24 ++++++++++--------------
 1 file changed, 10 insertions(+), 14 deletions(-)

-- 
2.7.4

Comments

Sean Wang Sept. 20, 2017, 4:32 p.m. | #1
Hi, Masahiro

For maintainability, I felt it's better if we use the same way to
register nvmem as that most drivers does under nvmem usually using
static structure. Otherwise, they should also be changed to use the
one-time data in stack to avoid extra bytes to keep them.

	Sean


On Mon, 2017-09-11 at 22:01 +0900, Masahiro Yamada wrote:
> nvmem_register() copies all the members of nvmem_config to

> nvmem_device.  So, nvmem_config is one-time use data during

> probing.  There is no point to keep it until the driver detach.

> Using stack should be no problem because nvmem_config is pretty

> small.

> 

> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

> ---

> 

>  drivers/nvmem/mtk-efuse.c | 24 ++++++++++--------------

>  1 file changed, 10 insertions(+), 14 deletions(-)

> 

> diff --git a/drivers/nvmem/mtk-efuse.c b/drivers/nvmem/mtk-efuse.c

> index 32fd572..fa7a0f6 100644

> --- a/drivers/nvmem/mtk-efuse.c

> +++ b/drivers/nvmem/mtk-efuse.c

> @@ -49,7 +49,7 @@ static int mtk_efuse_probe(struct platform_device *pdev)

>  	struct device *dev = &pdev->dev;

>  	struct resource *res;

>  	struct nvmem_device *nvmem;

> -	struct nvmem_config *econfig;

> +	struct nvmem_config econfig = {};

>  	void __iomem *base;

>  

>  	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);

> @@ -57,19 +57,15 @@ static int mtk_efuse_probe(struct platform_device *pdev)

>  	if (IS_ERR(base))

>  		return PTR_ERR(base);

>  

> -	econfig = devm_kzalloc(dev, sizeof(*econfig), GFP_KERNEL);

> -	if (!econfig)

> -		return -ENOMEM;

> -

> -	econfig->stride = 4;

> -	econfig->word_size = 4;

> -	econfig->reg_read = mtk_reg_read;

> -	econfig->reg_write = mtk_reg_write;

> -	econfig->size = resource_size(res);

> -	econfig->priv = base;

> -	econfig->dev = dev;

> -	econfig->owner = THIS_MODULE;

> -	nvmem = nvmem_register(econfig);

> +	econfig.stride = 4;

> +	econfig.word_size = 4;

> +	econfig.reg_read = mtk_reg_read;

> +	econfig.reg_write = mtk_reg_write;

> +	econfig.size = resource_size(res);

> +	econfig.priv = base;

> +	econfig.dev = dev;

> +	econfig.owner = THIS_MODULE;

> +	nvmem = nvmem_register(&econfig);

>  	if (IS_ERR(nvmem))

>  		return PTR_ERR(nvmem);

>
Masahiro Yamada Sept. 21, 2017, 2:09 a.m. | #2
Hi Sean,


2017-09-21 1:32 GMT+09:00 Sean Wang <sean.wang@mediatek.com>:
> Hi, Masahiro

>

> For maintainability, I felt it's better if we use the same way to

> register nvmem as that most drivers does under nvmem usually using

> static structure. Otherwise, they should also be changed to use the

> one-time data in stack to avoid extra bytes to keep them.

>

>         Sean



Srinivas and I discussed the best practice for allocating nvmem_config.
https://lkml.org/lkml/2017/9/11/4

From the discussion, static structure is possible only when
the system has one instance of the device.

If you know this is the case for mediatek,
yes, you can turn it into static,
but it is not always possible.
For example, Socionext SoCs have
two banks of efuse devices.

So, if we want to align the coding style for consistency,
nvmem in stack is safe and efficient, I think.


Moving one-time data into stack slightly
reduces the kernel image size.


-- 
Best Regards
Masahiro Yamada
Sean Wang Sept. 22, 2017, 3:59 a.m. | #3
Hi, Masahiro

On Thu, 2017-09-21 at 11:09 +0900, Masahiro Yamada wrote:
> Hi Sean,

> 

> 

> 2017-09-21 1:32 GMT+09:00 Sean Wang <sean.wang@mediatek.com>:

> > Hi, Masahiro

> >

> > For maintainability, I felt it's better if we use the same way to

> > register nvmem as that most drivers does under nvmem usually using

> > static structure. Otherwise, they should also be changed to use the

> > one-time data in stack to avoid extra bytes to keep them.

> >

> >         Sean

> 

> 

> Srinivas and I discussed the best practice for allocating nvmem_config.

> https://lkml.org/lkml/2017/9/11/4

> 

> From the discussion, static structure is possible only when

> the system has one instance of the device.

> 


thank you for your detailed explanation

> If you know this is the case for mediatek,

> yes, you can turn it into static,

> but it is not always possible.

> For example, Socionext SoCs have

> two banks of efuse devices.

> 


there should be only one instance of nvmem for mediatek soc, currently


> So, if we want to align the coding style for consistency,

> nvmem in stack is safe and efficient, I think.

> 

> 

> Moving one-time data into stack slightly

> reduces the kernel image size.

> 

> 


agreed on those statements, indeed bigger struct uart_8250_port is still
used on stack for configuring in a lot 8250 driver, so 

Acked-by: Sean Wang <sean.wang@mediatek.com>

Patch

diff --git a/drivers/nvmem/mtk-efuse.c b/drivers/nvmem/mtk-efuse.c
index 32fd572..fa7a0f6 100644
--- a/drivers/nvmem/mtk-efuse.c
+++ b/drivers/nvmem/mtk-efuse.c
@@ -49,7 +49,7 @@  static int mtk_efuse_probe(struct platform_device *pdev)
 	struct device *dev = &pdev->dev;
 	struct resource *res;
 	struct nvmem_device *nvmem;
-	struct nvmem_config *econfig;
+	struct nvmem_config econfig = {};
 	void __iomem *base;
 
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
@@ -57,19 +57,15 @@  static int mtk_efuse_probe(struct platform_device *pdev)
 	if (IS_ERR(base))
 		return PTR_ERR(base);
 
-	econfig = devm_kzalloc(dev, sizeof(*econfig), GFP_KERNEL);
-	if (!econfig)
-		return -ENOMEM;
-
-	econfig->stride = 4;
-	econfig->word_size = 4;
-	econfig->reg_read = mtk_reg_read;
-	econfig->reg_write = mtk_reg_write;
-	econfig->size = resource_size(res);
-	econfig->priv = base;
-	econfig->dev = dev;
-	econfig->owner = THIS_MODULE;
-	nvmem = nvmem_register(econfig);
+	econfig.stride = 4;
+	econfig.word_size = 4;
+	econfig.reg_read = mtk_reg_read;
+	econfig.reg_write = mtk_reg_write;
+	econfig.size = resource_size(res);
+	econfig.priv = base;
+	econfig.dev = dev;
+	econfig.owner = THIS_MODULE;
+	nvmem = nvmem_register(&econfig);
 	if (IS_ERR(nvmem))
 		return PTR_ERR(nvmem);