[PATCH/RFC v4 2/2] vfio: platform: Add generic reset controller support

[Geert Uytterhoeven <geert+renesas@xxxxxxxxx>]

Vfio-platform requires dedicated reset support, provided either by ACPI,
or, on DT platforms, by a device-specific reset driver matching against
the device's compatible value.

On many SoCs, devices are connected to an SoC-internal reset controller.
If the reset hierarchy is described in DT using "resets" properties, or
in lookup tables in platform code, such devices can be reset in a
generic way through the reset controller subsystem.  Hence add support
for this, avoiding the need to write device-specific reset drivers for
each single device on affected SoCs.

Devices that do require a more complex reset procedure can still provide
a device-specific reset driver, as that takes precedence.

Note that this functionality depends on CONFIG_RESET_CONTROLLER=y, and
becomes a no-op (as in: "No reset function found for device") if reset
controller support is disabled.

Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
Reviewed-by: Philipp Zabel <p.zabel@xxxxxxxxxxxxxx>
Reviewed-by: Simon Horman <horms+renesas@xxxxxxxxxxxx>
---
v4:
  - Add Reviewed-by,
  - Use new RFC reset_control_get_dedicated() instead of
    of_reset_control_get_exclusive(), to (a) make it more generic, and
    (b) make sure the reset returned is really a dedicated reset, and
    does not affect other devices,

v3:
  - Add Reviewed-by,
  - Merge similar checks in vfio_platform_has_reset(),

v2:
  - Don't store error values in vdev->reset_control,
  - Use of_reset_control_get_exclusive() instead of
    __of_reset_control_get(),
  - Improve description.

---
 drivers/vfio/platform/vfio_platform_common.c  | 20 +++++++++++++++++--
 drivers/vfio/platform/vfio_platform_private.h |  1 +
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/drivers/vfio/platform/vfio_platform_common.c b/drivers/vfio/platform/vfio_platform_common.c
index c0cd824be2b767be..eb77fe87f3663e3e 100644
--- a/drivers/vfio/platform/vfio_platform_common.c
+++ b/drivers/vfio/platform/vfio_platform_common.c
@@ -18,6 +18,7 @@
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/pm_runtime.h>
+#include <linux/reset.h>
 #include <linux/slab.h>
 #include <linux/types.h>
 #include <linux/uaccess.h>
@@ -113,11 +114,13 @@ static bool vfio_platform_has_reset(struct vfio_platform_device *vdev)
 	if (VFIO_PLATFORM_IS_ACPI(vdev))
 		return vfio_platform_acpi_has_reset(vdev);
 
-	return vdev->of_reset ? true : false;
+	return vdev->of_reset || vdev->reset_control;
 }
 
 static int vfio_platform_get_reset(struct vfio_platform_device *vdev)
 {
+	struct reset_control *rstc;
+
 	if (VFIO_PLATFORM_IS_ACPI(vdev))
 		return vfio_platform_acpi_has_reset(vdev) ? 0 : -ENOENT;
 
@@ -128,8 +131,16 @@ static int vfio_platform_get_reset(struct vfio_platform_device *vdev)
 		vdev->of_reset = vfio_platform_lookup_reset(vdev->compat,
 							&vdev->reset_module);
 	}
+	if (vdev->of_reset)
+		return 0;
+
+	rstc = reset_control_get_dedicated(vdev->device, NULL);
+	if (!IS_ERR(rstc)) {
+		vdev->reset_control = rstc;
+		return 0;
+	}
 
-	return vdev->of_reset ? 0 : -ENOENT;
+	return PTR_ERR(rstc);
 }
 
 static void vfio_platform_put_reset(struct vfio_platform_device *vdev)
@@ -139,6 +150,8 @@ static void vfio_platform_put_reset(struct vfio_platform_device *vdev)
 
 	if (vdev->of_reset)
 		module_put(vdev->reset_module);
+
+	reset_control_put(vdev->reset_control);
 }
 
 static int vfio_platform_regions_init(struct vfio_platform_device *vdev)
@@ -218,6 +231,9 @@ static int vfio_platform_call_reset(struct vfio_platform_device *vdev,
 	} else if (vdev->of_reset) {
 		dev_info(vdev->device, "reset\n");
 		return vdev->of_reset(vdev);
+	} else if (vdev->reset_control) {
+		dev_info(vdev->device, "reset\n");
+		return reset_control_reset(vdev->reset_control);
 	}
 
 	dev_warn(vdev->device, "no reset function found!\n");
diff --git a/drivers/vfio/platform/vfio_platform_private.h b/drivers/vfio/platform/vfio_platform_private.h
index 85ffe5d9d1abd94e..a56e80ae5986540b 100644
--- a/drivers/vfio/platform/vfio_platform_private.h
+++ b/drivers/vfio/platform/vfio_platform_private.h
@@ -60,6 +60,7 @@ struct vfio_platform_device {
 	const char			*compat;
 	const char			*acpihid;
 	struct module			*reset_module;
+	struct reset_control		*reset_control;
 	struct device			*device;
 
 	/*
-- 
2.17.1