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Subject[PATCH/RFC v4 2/2] vfio: platform: Add generic reset controller support
Date
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@glider.be>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
---
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
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