Some of the IO devices like I2C or SPI require reset at runtime to
recover from an error condition without changing the power state of
the system. Added check for ACPI handle and a call to method '__RST'
if supported. Devices using device tree method are unaffected by this.

Signed-off-by: Krishna Yarlagadda <kyarlagadda@nvidia.com>
---
 drivers/reset/core.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/reset/core.c b/drivers/reset/core.c
index 61e6888..e4fb533 100644
--- a/drivers/reset/core.c
+++ b/drivers/reset/core.c
@@ -12,6 +12,7 @@
 #include <linux/kref.h>
 #include <linux/module.h>
 #include <linux/of.h>
+#include <linux/acpi.h>
 #include <linux/reset.h>
 #include <linux/reset-controller.h>
 #include <linux/slab.h>
@@ -1107,6 +1108,11 @@ int __device_reset(struct device *dev, bool optional)
 	struct reset_control *rstc;
 	int ret;
 
+	acpi_handle handle = ACPI_HANDLE(dev);
+
+	if (handle)
+		return acpi_evaluate_object(handle, "_RST", NULL, NULL);
+
 	rstc = __reset_control_get(dev, NULL, 0, 0, optional, true);
 	if (IS_ERR(rstc))
 		return PTR_ERR(rstc);
-- 
2.7.4

Hi Krishna,

On Fr, 2022-02-04 at 16:04 +0530, Krishna Yarlagadda wrote:
> Some of the IO devices like I2C or SPI require reset at runtime to
> recover from an error condition without changing the power state of
> the system. Added check for ACPI handle and a call to method '__RST'
> if supported. Devices using device tree method are unaffected by
> this.
> 
> Signed-off-by: Krishna Yarlagadda <kyarlagadda@nvidia.com>
> ---
>  drivers/reset/core.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/reset/core.c b/drivers/reset/core.c
> index 61e6888..e4fb533 100644
> --- a/drivers/reset/core.c
> +++ b/drivers/reset/core.c
> @@ -12,6 +12,7 @@
>  #include <linux/kref.h>
>  #include <linux/module.h>
>  #include <linux/of.h>
> +#include <linux/acpi.h>
>  #include <linux/reset.h>
>  #include <linux/reset-controller.h>
>  #include <linux/slab.h>
> @@ -1107,6 +1108,11 @@ int __device_reset(struct device *dev, bool optional)

Could you add a sentence to the kerneldoc description above this, for
example "For ACPI devices this calls the _RST method"?

>         struct reset_control *rstc;
>         int ret;
>  
> +       acpi_handle handle = ACPI_HANDLE(dev);
> +
> +       if (handle)

What does acpi_evaluate_object() do if the _RST method is not present?
I think we have to check

		if (!acpi_has_method(handle, "_RST"))
			return optional ? 0 : -ENOENT;

here.

> +               return acpi_evaluate_object(handle, "_RST", NULL, NULL);

acpi_evaluate_object() returns acpi_status, so that should probably be
something like:

		status = acpi_evaluate_object(handle, "_RST", NULL, NULL);
		if (ACPI_FAILURE(status))
			return -EIO;

> +
>         rstc = __reset_control_get(dev, NULL, 0, 0, optional, true);
>         if (IS_ERR(rstc))
>                 return PTR_ERR(rstc);

regards
Philipp