[PATCH] clk: clk_set_parent: skip any operation if current and new parents are equal

[PATCH] clk: clk_set_parent: skip any operation if current and new parents are equal

[Michael Grzeschik]

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
---
 drivers/clk/clk.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 89a007a12c5..ac5b83cf8b4 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -302,6 +302,9 @@ int clk_set_parent(struct clk *clk, struct clk *newparent)
 	if (IS_ERR(newparent))
 		return PTR_ERR(newparent);
 
+	if (newparent == curparent)
+		return 0;
+
 	if (!clk->num_parents)
 		return -EINVAL;
 	if (!clk->ops->set_parent)
-- 
2.47.3

Re: [PATCH] clk: clk_set_parent: skip any operation if current and new parents are equal

[Ahmad Fatoum]

Hi,

On 10/3/25 12:37 PM, Michael Grzeschik wrote:
> Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>

While I agree this makes sense, I appreciate some background. Did you
run into problems? Or is it just something you noticed while reading the
code? A prime location for that background would be the empty commit
message ;)

Cheers,
Ahmad

> ---
>  drivers/clk/clk.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index 89a007a12c5..ac5b83cf8b4 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -302,6 +302,9 @@ int clk_set_parent(struct clk *clk, struct clk *newparent)
>  	if (IS_ERR(newparent))
>  		return PTR_ERR(newparent);
>  
> +	if (newparent == curparent)
> +		return 0;
> +
>  	if (!clk->num_parents)
>  		return -EINVAL;
>  	if (!clk->ops->set_parent)

-- 
Pengutronix e.K.                  |                             |
Steuerwalder Str. 21              | http://www.pengutronix.de/  |
31137 Hildesheim, Germany         | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686  | Fax:   +49-5121-206917-5555 |

Re: [PATCH] clk: clk_set_parent: skip any operation if current and new parents are equal

[Michael Grzeschik]

[-- Attachment #1: Type: text/plain, Size: 1921 bytes --]

On Mon, Oct 06, 2025 at 01:43:47PM +0200, Ahmad Fatoum wrote:
>On 10/3/25 12:37 PM, Michael Grzeschik wrote:
>> Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
>
>While I agree this makes sense, I appreciate some background. Did you
>run into problems? Or is it just something you noticed while reading the
>code? A prime location for that background would be the empty commit
>message ;)

Yes this happend when using the video drivers. Somehow some drivers
tried to reparent the video_pll to the same parent that it already had.

clk: failed to reparent video_pll to osc_24m: -22
clk: failed to reparent video_pll to osc_24m: -22

I did not check which one it was. Since this call came twice, it looked
right to me to fix this on this obvious location.

Michael

>> ---
>>  drivers/clk/clk.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
>> index 89a007a12c5..ac5b83cf8b4 100644
>> --- a/drivers/clk/clk.c
>> +++ b/drivers/clk/clk.c
>> @@ -302,6 +302,9 @@ int clk_set_parent(struct clk *clk, struct clk *newparent)
>>  	if (IS_ERR(newparent))
>>  		return PTR_ERR(newparent);
>>
>> +	if (newparent == curparent)
>> +		return 0;
>> +
>>  	if (!clk->num_parents)
>>  		return -EINVAL;
>>  	if (!clk->ops->set_parent)
>
>-- 
>Pengutronix e.K.                  |                             |
>Steuerwalder Str. 21              | http://www.pengutronix.de/  |
>31137 Hildesheim, Germany         | Phone: +49-5121-206917-0    |
>Amtsgericht Hildesheim, HRA 2686  | Fax:   +49-5121-206917-5555 |
>
>

-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH] clk: clk_set_parent: skip any operation if current and new parents are equal

[Sascha Hauer]

On Mon, Oct 06, 2025 at 10:53:02PM +0200, Michael Grzeschik wrote:
> On Mon, Oct 06, 2025 at 01:43:47PM +0200, Ahmad Fatoum wrote:
> > On 10/3/25 12:37 PM, Michael Grzeschik wrote:
> > > Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
> > 
> > While I agree this makes sense, I appreciate some background. Did you
> > run into problems? Or is it just something you noticed while reading the
> > code? A prime location for that background would be the empty commit
> > message ;)
> 
> Yes this happend when using the video drivers. Somehow some drivers
> tried to reparent the video_pll to the same parent that it already had.
> 
> clk: failed to reparent video_pll to osc_24m: -22
> clk: failed to reparent video_pll to osc_24m: -22

If it's the same parent it already has, why does it fail with -EINVAL
then?

Sascha

-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

Re: [PATCH] clk: clk_set_parent: skip any operation if current and new parents are equal

[Sascha Hauer]

On Tue, Oct 07, 2025 at 01:50:28PM +0200, Sascha Hauer wrote:
> On Mon, Oct 06, 2025 at 10:53:02PM +0200, Michael Grzeschik wrote:
> > On Mon, Oct 06, 2025 at 01:43:47PM +0200, Ahmad Fatoum wrote:
> > > On 10/3/25 12:37 PM, Michael Grzeschik wrote:
> > > > Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
> > > 
> > > While I agree this makes sense, I appreciate some background. Did you
> > > run into problems? Or is it just something you noticed while reading the
> > > code? A prime location for that background would be the empty commit
> > > message ;)
> > 
> > Yes this happend when using the video drivers. Somehow some drivers
> > tried to reparent the video_pll to the same parent that it already had.
> > 
> > clk: failed to reparent video_pll to osc_24m: -22
> > clk: failed to reparent video_pll to osc_24m: -22
> 
> If it's the same parent it already has, why does it fail with -EINVAL
> then?

Ah, probably because of:

	if (!clk->ops->set_parent)
		return -EINVAL;

So the clk only has a single parent, thus no set_parent op. Your patch
is indeed correct. Please update the commit message with this
information.

Sascha

-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |