[PATCH] spi: Add spi_for_each_controller() helper

[PATCH] spi: Add spi_for_each_controller() helper

[ChaoHuang]

From: Chao Huang <huangchao@kylinos.cn>

Add a new helper function to iterate over all SPI controllers.
This provides a convenient way for SPI core code and drivers
to perform operations on all registered controllers.

The implementation follows existing SPI subsystem patterns:
- Uses spi_controller_list with board_lock protection
- Directly operates on spi_controller objects
- Breaks iteration on callback error
- Follows kernel naming conventions (spi_for_each_*)

This helper is useful for scenarios like statistics gathering,
configuration updates, or debugging operations that need to
process all SPI controllers in the system.

Signed-off-by: Chao Huang <huangchao@kylinos.cn>
---
 drivers/spi/spi.c       | 17 +++++++++++++++++
 include/linux/spi/spi.h |  2 ++
 2 files changed, 19 insertions(+)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 104279858f56..7cd07b390a4b 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -5116,6 +5116,23 @@ static struct notifier_block spi_acpi_notifier = {
 extern struct notifier_block spi_acpi_notifier;
 #endif
 
+int spi_for_each_controller(int (*fn)(struct spi_controller *, void *), void *data)
+{
+	struct spi_controller *ctlr;
+	int ret = 0;
+
+	mutex_lock(&board_lock);
+	list_for_each_entry(ctlr, &spi_controller_list, list) {
+		ret = fn(ctlr, data);
+		if (ret)
+			break;
+	}
+	mutex_unlock(&board_lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(spi_for_each_controller);
+
 static int __init spi_init(void)
 {
 	int	status;
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 79513f5941cc..8fcf3faf9739 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -934,6 +934,8 @@ static inline int acpi_spi_count_resources(struct acpi_device *adev)
 }
 #endif
 
+int spi_for_each_controller(int (*fn)(struct spi_controller *, void *), void *data);
+
 /*
  * SPI resource management while processing a SPI message
  */
-- 
2.25.1

Re: [PATCH] spi: Add spi_for_each_controller() helper

[Mark Brown]

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On Thu, May 14, 2026 at 04:45:44PM +0800, ChaoHuang wrote:
> From: Chao Huang <huangchao@kylinos.cn>
> 
> Add a new helper function to iterate over all SPI controllers.
> This provides a convenient way for SPI core code and drivers
> to perform operations on all registered controllers.

> This helper is useful for scenarios like statistics gathering,
> configuration updates, or debugging operations that need to
> process all SPI controllers in the system.

Do you have an actual user for this or is this just purely theoretical
at this point?  It'd make a lot more sense to add this along with a
user.

> +int spi_for_each_controller(int (*fn)(struct spi_controller *, void *), void *data)
> +{
> +	struct spi_controller *ctlr;
> +	int ret = 0;
> +
> +	mutex_lock(&board_lock);
> +	list_for_each_entry(ctlr, &spi_controller_list, list) {
> +		ret = fn(ctlr, data);

When unregistering controllers we do start the teardown process before
we pull the device off the controller list, and drop the lock while
doing so.  That's probably fine for a lot of uses.

There's also some obvious potential for things to go wrong here with
something in the callback deadlocking, though that's a bit of a "don't
do that kind of thing".

> +		if (ret)
> +			break;
> +	}
> +	mutex_unlock(&board_lock);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(spi_for_each_controller);
> +
>  static int __init spi_init(void)
>  {
>  	int	status;
> diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
> index 79513f5941cc..8fcf3faf9739 100644
> --- a/include/linux/spi/spi.h
> +++ b/include/linux/spi/spi.h
> @@ -934,6 +934,8 @@ static inline int acpi_spi_count_resources(struct acpi_device *adev)
>  }
>  #endif
>  
> +int spi_for_each_controller(int (*fn)(struct spi_controller *, void *), void *data);
> +
>  /*
>   * SPI resource management while processing a SPI message
>   */
> -- 
> 2.25.1
> 

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Re: [PATCH] spi: Add spi_for_each_controller() helper

[Mark Brown]

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On Mon, May 18, 2026 at 03:10:26PM +0800, Chao Huang wrote:
> > Do you have an actual user for this or is this just purely theoretical
> > at this point? It'd make a lot more sense to add this along with a
> > user.

> Yes, I do have an actual user for this helper in my project.

> The goal is to provide a new SPI controller API that allows users to
> access SPI controllers by bus number and chip select (CS). The
> `spi_for_each_controller()` helper is used to iterate over all registered
> controllers, find the target controller by bus number, and then operate
> on it.

OK, I would hold off on this patch and sumbit it along with the user -
it's not really something that's clearly useful without that user.

> > When unregistering controllers we do start the teardown process before
> > we pull the device off the controller list, and drop the lock while
> > doing so. That's probably fine for a lot of uses.
> >

> Regarding the controller unregistration case you mentioned — do you mean
> the `spi_unregister_controller()` function?

Yes.

> In my `fn` callback, I call `spi_controller_get()` to safely grab a
> reference to the controller, and later call `spi_controller_put()` at an
> appropriate time (e.g., after the operation is done). This should
> prevent the controller from being freed while it is still in use, even
> if unregistration happens concurrently.

The controller itself will be there but we do things like stopping the
queue before we destroy the controller.

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Re: [PATCH] spi: Add spi_for_each_controller() helper

[Mark Brown]

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On Thu, May 14, 2026 at 02:13:08PM +0800, 958028483@qq.com wrote:
> From: huangchao <huangchao@kylinos.cn>

> Signed-off-by: huangchao <huangchao@kylinos.cn>

Your email address and (non-)name don't match your signoff at all so I
can't really verify that you're the same person, could you please bring
the two in line somehow so I can verify that there's a valid signoff?

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[PATCH] spi: Add spi_for_each_controller() helper

[958028483]

From: huangchao <huangchao@kylinos.cn>

Add a new helper function to iterate over all SPI controllers.
This provides a convenient way for SPI core code and drivers
to perform operations on all registered controllers.

The implementation follows existing SPI subsystem patterns:
- Uses spi_controller_list with board_lock protection
- Directly operates on spi_controller objects
- Breaks iteration on callback error
- Follows kernel naming conventions (spi_for_each_*)

This helper is useful for scenarios like statistics gathering,
configuration updates, or debugging operations that need to
process all SPI controllers in the system.

Signed-off-by: huangchao <huangchao@kylinos.cn>
---
 drivers/spi/spi.c       | 17 +++++++++++++++++
 include/linux/spi/spi.h |  2 ++
 2 files changed, 19 insertions(+)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 104279858f56..7cd07b390a4b 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -5116,6 +5116,23 @@ static struct notifier_block spi_acpi_notifier = {
 extern struct notifier_block spi_acpi_notifier;
 #endif
 
+int spi_for_each_controller(int (*fn)(struct spi_controller *, void *), void *data)
+{
+	struct spi_controller *ctlr;
+	int ret = 0;
+
+	mutex_lock(&board_lock);
+	list_for_each_entry(ctlr, &spi_controller_list, list) {
+		ret = fn(ctlr, data);
+		if (ret)
+			break;
+	}
+	mutex_unlock(&board_lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(spi_for_each_controller);
+
 static int __init spi_init(void)
 {
 	int	status;
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 79513f5941cc..8fcf3faf9739 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -934,6 +934,8 @@ static inline int acpi_spi_count_resources(struct acpi_device *adev)
 }
 #endif
 
+int spi_for_each_controller(int (*fn)(struct spi_controller *, void *), void *data);
+
 /*
  * SPI resource management while processing a SPI message
  */
-- 
2.25.1