[PATCH] [v3] i2c: imx-lpi2c: Fix runtime PM imbalance on error

[PATCH] [v3] i2c: imx-lpi2c: Fix runtime PM imbalance on error

[Dinghao Liu]

pm_runtime_get_sync() increments the runtime PM usage counter even
the call returns an error code. Thus a corresponding decrement is
needed on the error handling path to keep the counter balanced.

Fix this by adding the missed function call.

Fixes: 13d6eb20fc79a ("i2c: imx-lpi2c: add runtime pm support")
Co-developed-by: Markus Elfring <Markus.Elfring@web.de>
Signed-off-by: Markus Elfring <Markus.Elfring@web.de>
Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
---

Changelog:

v2: - Use pm_runtime_put_noidle() instead of
      pm_runtime_put_autosuspend().

v3: - Refine commit message.
---
 drivers/i2c/busses/i2c-imx-lpi2c.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/busses/i2c-imx-lpi2c.c b/drivers/i2c/busses/i2c-imx-lpi2c.c
index 94743ba581fe..bdee02dff284 100644
--- a/drivers/i2c/busses/i2c-imx-lpi2c.c
+++ b/drivers/i2c/busses/i2c-imx-lpi2c.c
@@ -260,8 +260,10 @@ static int lpi2c_imx_master_enable(struct lpi2c_imx_struct *lpi2c_imx)
 	int ret;
 
 	ret = pm_runtime_get_sync(lpi2c_imx->adapter.dev.parent);
-	if (ret < 0)
+	if (ret < 0) {
+		pm_runtime_put_noidle(lpi2c_imx->adapter.dev.parent);
 		return ret;
+	}
 
 	temp = MCR_RST;
 	writel(temp, lpi2c_imx->base + LPI2C_MCR);
-- 
2.17.1

RE: [EXT] [PATCH] [v3] i2c: imx-lpi2c: Fix runtime PM imbalance on error

[Andy Duan]

From: Dinghao Liu <dinghao.liu@zju.edu.cn> Sent: Monday, June 1, 2020 2:17 PM
> pm_runtime_get_sync() increments the runtime PM usage counter even the
> call returns an error code. Thus a corresponding decrement is needed on the
> error handling path to keep the counter balanced.
> 
> Fix this by adding the missed function call.
> 
> Fixes: 13d6eb20fc79a ("i2c: imx-lpi2c: add runtime pm support")
> Co-developed-by: Markus Elfring <Markus.Elfring@web.de>
> Signed-off-by: Markus Elfring <Markus.Elfring@web.de>
> Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>

Reviewed-by: Fugang Duan <fugang.duan@nxp.com>
> ---
> 
> Changelog:
> 
> v2: - Use pm_runtime_put_noidle() instead of
>       pm_runtime_put_autosuspend().
> 
> v3: - Refine commit message.
> ---
>  drivers/i2c/busses/i2c-imx-lpi2c.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/busses/i2c-imx-lpi2c.c
> b/drivers/i2c/busses/i2c-imx-lpi2c.c
> index 94743ba581fe..bdee02dff284 100644
> --- a/drivers/i2c/busses/i2c-imx-lpi2c.c
> +++ b/drivers/i2c/busses/i2c-imx-lpi2c.c
> @@ -260,8 +260,10 @@ static int lpi2c_imx_master_enable(struct
> lpi2c_imx_struct *lpi2c_imx)
>         int ret;
> 
>         ret = pm_runtime_get_sync(lpi2c_imx->adapter.dev.parent);
> -       if (ret < 0)
> +       if (ret < 0) {
> +               pm_runtime_put_noidle(lpi2c_imx->adapter.dev.parent);
>                 return ret;
> +       }
> 
>         temp = MCR_RST;
>         writel(temp, lpi2c_imx->base + LPI2C_MCR);
> --
> 2.17.1

Re: [PATCH v3] i2c: imx-lpi2c: Fix runtime PM imbalance in lpi2c_imx_master_enable()

[Markus Elfring]

> pm_runtime_get_sync() increments the runtime PM usage counter even
> the call returns an error code. Thus a corresponding decrement is
> needed on the error handling path to keep the counter balanced.
>
> Fix this by adding the missed function call.

How do you think about a wording variant like the following?

   Change description:
   The PM runtime usage counter is incremented even if a call of
   the function “pm_runtime_get_sync” failed. Thus decrement it also
   in an error case so that the reference counting is kept consistent.


Regards,
Markus

Re: [PATCH] [v3] i2c: imx-lpi2c: Fix runtime PM imbalance on error

[Wolfram Sang]

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On Mon, Jun 01, 2020 at 02:16:40PM +0800, Dinghao Liu wrote:
> pm_runtime_get_sync() increments the runtime PM usage counter even
> the call returns an error code. Thus a corresponding decrement is
> needed on the error handling path to keep the counter balanced.

Can you point me to a discussion where it was decided that this is a
proper fix? I'd think we rather should fix pm_runtime_get_sync() but
maybe there are technical reasons against it.


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Re: Re: [PATCH] [v3] i2c: imx-lpi2c: Fix runtime PM imbalance on error

[dinghao.liu]

> 
> Can you point me to a discussion where it was decided that this is a
> proper fix? I'd think we rather should fix pm_runtime_get_sync() but
> maybe there are technical reasons against it.
> 

There is a discussion here:
https://lkml.org/lkml/2020/5/20/1100

There are many use cases that suppose pm_runtime_get_sync() will always
increment the usage counter and do not check its return value. So I don't
think we should adjust this function directly.

As for this API, Dan suggested a replacement (wrapper) for later developers.
I think this is the best solution.
https://lore.kernel.org/patchwork/patch/1245375/

Regards,
Dinghao

RE: [PATCH] [v3] i2c: imx-lpi2c: Fix runtime PM imbalance on error

[Aisheng Dong]

> From: Wolfram Sang <wsa@kernel.org>
> Sent: Sunday, June 14, 2020 5:12 PM
> 
> On Mon, Jun 01, 2020 at 02:16:40PM +0800, Dinghao Liu wrote:
> > pm_runtime_get_sync() increments the runtime PM usage counter even the
> > call returns an error code. Thus a corresponding decrement is needed
> > on the error handling path to keep the counter balanced.
> 
> Can you point me to a discussion where it was decided that this is a proper fix?
> I'd think we rather should fix pm_runtime_get_sync() but maybe there are
> technical reasons against it.

I had the same feeling.
Copy pm guys to comments.

Regards
Aisheng

Re: [PATCH] [v3] i2c: imx-lpi2c: Fix runtime PM imbalance on error

[Wolfram Sang]

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On Mon, Jun 15, 2020 at 06:33:40AM +0000, Aisheng Dong wrote:
> > From: Wolfram Sang <wsa@kernel.org>
> > Sent: Sunday, June 14, 2020 5:12 PM
> > 
> > On Mon, Jun 01, 2020 at 02:16:40PM +0800, Dinghao Liu wrote:
> > > pm_runtime_get_sync() increments the runtime PM usage counter even the
> > > call returns an error code. Thus a corresponding decrement is needed
> > > on the error handling path to keep the counter balanced.
> > 
> > Can you point me to a discussion where it was decided that this is a proper fix?
> > I'd think we rather should fix pm_runtime_get_sync() but maybe there are
> > technical reasons against it.
> 
> I had the same feeling.
> Copy pm guys to comments.

I started a seperate thread:

https://lkml.org/lkml/2020/6/14/76

Still, on-going discussion if the proper fix is to remove the error
check.


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Re: [v3] i2c: imx-lpi2c: Fix runtime PM imbalance on error

[Markus Elfring]

> I started a seperate thread:
>
> https://lkml.org/lkml/2020/6/14/76
>
> Still, on-going discussion if the proper fix is to remove the error check.

I find that a bit of additional information can make such a link safer.

RFC: a failing pm_runtime_get increases the refcnt?
https://lore.kernel.org/lkml/20200614090751.GA2878@kunai/

How will the clarification of corresponding software aspects evolve further?

Regards,
Markus