[PATCH] vfio: platform: Fix using devices in PM Domains

[PATCH] vfio: platform: Fix using devices in PM Domains

[Geert Uytterhoeven]

If a device is part of a PM Domain (e.g. power and/or clock domain), its
power state is managed using Runtime PM.  Without Runtime PM, the device
may not be powered up, causing subtle failures, crashes, or system
lock-ups when the device is accessed by the guest.

Fix this by adding Runtime PM support, powering the device when the VFIO
device is opened by the guest.

Note that while more fine-grained power management could be implemented
on the guest side, if exported, this would be inherently unsafe, as
abusing it may kill the whole system.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
 drivers/vfio/platform/vfio_platform_common.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/vfio/platform/vfio_platform_common.c b/drivers/vfio/platform/vfio_platform_common.c
index 3c13327b2777f8ec..9d46fce2446daebe 100644
--- a/drivers/vfio/platform/vfio_platform_common.c
+++ b/drivers/vfio/platform/vfio_platform_common.c
@@ -17,6 +17,7 @@
 #include <linux/iommu.h>
 #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>
@@ -255,6 +256,8 @@ static void vfio_platform_release(void *device_data)
 		const char *extra_dbg = NULL;
 		int ret;
 
+		pm_runtime_put(vdev->device);
+
 		ret = vfio_platform_call_reset(vdev, &extra_dbg);
 		if (ret && vdev->reset_required) {
 			dev_warn(vdev->device, "reset driver is required and reset call failed in release (%d) %s\n",
@@ -297,6 +300,10 @@ static int vfio_platform_open(void *device_data)
 				 ret, extra_dbg ? extra_dbg : "");
 			goto err_rst;
 		}
+
+		ret = pm_runtime_get_sync(vdev->device);
+		if (ret < 0)
+			goto err_rst;
 	}
 
 	vdev->refcnt++;
@@ -712,6 +719,7 @@ int vfio_platform_probe_common(struct vfio_platform_device *vdev,
 
 	mutex_init(&vdev->igate);
 
+	pm_runtime_enable(vdev->device);
 	return 0;
 
 put_iommu:
@@ -729,6 +737,7 @@ struct vfio_platform_device *vfio_platform_remove_common(struct device *dev)
 	vdev = vfio_del_group_dev(dev);
 
 	if (vdev) {
+		pm_runtime_disable(vdev->device);
 		vfio_platform_put_reset(vdev);
 		vfio_iommu_group_put(dev->iommu_group, dev);
 	}
-- 
2.7.4

[PATCH v3 0/2] vfio: platform: Improve reset support

[Geert Uytterhoeven]

	Hi all,

This patch series improves reset support for vfio-platform:
  - The first patch fixes a bug I ran into while working on this.
  - The second patch implements generic DT reset controller support, for
    devices that are connected to an SoC-internal reset controller and
    can be reset in a generic way.  This avoids having to write/change a
    vfio-specific reset driver for each and every device to be
    passed-through to a guest.

Changes compared to v2:
  - Add Reviewed-by,
  - Merge similar checks in vfio_platform_has_reset().

Changes compared to v1:
  - Add Reviewed-by,
  - Don't store error values in vdev->reset_control,
  - Use of_reset_control_get_exclusive() instead of
    __of_reset_control_get(),
  - Improve description.

This has been tested on R-Car H3/Salvator-XS by exporting a GPIO module
to a QEMU+KWM guest: the GPIO module is reset before QEMU opens the vfio
device, and reset again after QEMU has released it, as can be witnessed
by the LEDs connected to the GPIOs.

Thanks!

Geert Uytterhoeven (2):
  vfio: platform: Fix reset module leak in error path
  vfio: platform: Add generic DT reset support

 drivers/vfio/platform/vfio_platform_common.c  | 35 +++++++++++++++++++++------
 drivers/vfio/platform/vfio_platform_private.h |  1 +
 2 files changed, 29 insertions(+), 7 deletions(-)

-- 
2.7.4

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds

[PATCH v3 1/2] vfio: platform: Fix reset module leak in error path

[Geert Uytterhoeven]

If the IOMMU group setup fails, the reset module is not released.

Fixes: b5add544d677d363 ("vfio, platform: make reset driver a requirement by default")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
---
v3:
  - Add Reviewed-by,

v2:
  - Add Reviewed-by.
---
 drivers/vfio/platform/vfio_platform_common.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/vfio/platform/vfio_platform_common.c b/drivers/vfio/platform/vfio_platform_common.c
index 35469af87f88678e..b60bb5326668498c 100644
--- a/drivers/vfio/platform/vfio_platform_common.c
+++ b/drivers/vfio/platform/vfio_platform_common.c
@@ -680,18 +680,23 @@ int vfio_platform_probe_common(struct vfio_platform_device *vdev,
 	group = vfio_iommu_group_get(dev);
 	if (!group) {
 		pr_err("VFIO: No IOMMU group for device %s\n", vdev->name);
-		return -EINVAL;
+		ret = -EINVAL;
+		goto put_reset;
 	}
 
 	ret = vfio_add_group_dev(dev, &vfio_platform_ops, vdev);
-	if (ret) {
-		vfio_iommu_group_put(group, dev);
-		return ret;
-	}
+	if (ret)
+		goto put_iommu;
 
 	mutex_init(&vdev->igate);
 
 	return 0;
+
+put_iommu:
+	vfio_iommu_group_put(group, dev);
+put_reset:
+	vfio_platform_put_reset(vdev);
+	return ret;
 }
 EXPORT_SYMBOL_GPL(vfio_platform_probe_common);
 
-- 
2.7.4

Re: [PATCH v3 1/2] vfio: platform: Fix reset module leak in error path

[Auger Eric]

Hi Geert,
On 11/04/18 11:15, Geert Uytterhoeven wrote:
> If the IOMMU group setup fails, the reset module is not released.
> 
> Fixes: b5add544d677d363 ("vfio, platform: make reset driver a requirement by default")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> Reviewed-by: Eric Auger <eric.auger@redhat.com>
> Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Eric Auger <eric.auger@redhat.com>

Thanks

Eric
> ---
> v3:
>   - Add Reviewed-by,
> 
> v2:
>   - Add Reviewed-by.
> ---
>  drivers/vfio/platform/vfio_platform_common.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/vfio/platform/vfio_platform_common.c b/drivers/vfio/platform/vfio_platform_common.c
> index 35469af87f88678e..b60bb5326668498c 100644
> --- a/drivers/vfio/platform/vfio_platform_common.c
> +++ b/drivers/vfio/platform/vfio_platform_common.c
> @@ -680,18 +680,23 @@ int vfio_platform_probe_common(struct vfio_platform_device *vdev,
>  	group = vfio_iommu_group_get(dev);
>  	if (!group) {
>  		pr_err("VFIO: No IOMMU group for device %s\n", vdev->name);
> -		return -EINVAL;
> +		ret = -EINVAL;
> +		goto put_reset;
>  	}
>  
>  	ret = vfio_add_group_dev(dev, &vfio_platform_ops, vdev);
> -	if (ret) {
> -		vfio_iommu_group_put(group, dev);
> -		return ret;
> -	}
> +	if (ret)
> +		goto put_iommu;
>  
>  	mutex_init(&vdev->igate);
>  
>  	return 0;
> +
> +put_iommu:
> +	vfio_iommu_group_put(group, dev);
> +put_reset:
> +	vfio_platform_put_reset(vdev);
> +	return ret;
>  }
>  EXPORT_SYMBOL_GPL(vfio_platform_probe_common);
>  
> 

Re: [PATCH v3 1/2] vfio: platform: Fix reset module leak in error path

[Alex Williamson]

On Wed, 11 Apr 2018 11:15:48 +0200
Geert Uytterhoeven <geert+renesas@glider.be> wrote:

> If the IOMMU group setup fails, the reset module is not released.
> 
> Fixes: b5add544d677d363 ("vfio, platform: make reset driver a requirement by default")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> Reviewed-by: Eric Auger <eric.auger@redhat.com>
> Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
> ---
> v3:
>   - Add Reviewed-by,
> 
> v2:
>   - Add Reviewed-by.
> ---
>  drivers/vfio/platform/vfio_platform_common.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)

Applied to next branch for v4.18 with Eric's ack.  Thanks,

Alex

[PATCH v3 2/2] vfio: platform: Add generic DT reset support

[Geert Uytterhoeven]

Vfio-platform requires 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,
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>
---
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 b60bb5326668498c..ef9b9e3220ebe939 100644
--- a/drivers/vfio/platform/vfio_platform_common.c
+++ b/drivers/vfio/platform/vfio_platform_common.c
@@ -17,6 +17,7 @@
 #include <linux/iommu.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
+#include <linux/reset.h>
 #include <linux/slab.h>
 #include <linux/types.h>
 #include <linux/uaccess.h>
@@ -112,11 +113,13 @@ 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;
 
@@ -127,8 +130,16 @@ 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 = of_reset_control_get_exclusive(vdev->device->of_node, 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)
@@ -138,6 +149,8 @@ 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)
@@ -217,6 +230,9 @@ 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;
 
 	/*
-- 
2.7.4

Re: [PATCH v3 2/2] vfio: platform: Add generic DT reset support

[Simon Horman]

On Wed, Apr 11, 2018 at 11:15:49AM +0200, Geert Uytterhoeven wrote:
> Vfio-platform requires 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,
> 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>

Re: [PATCH v3 2/2] vfio: platform: Add generic DT reset support

[Auger Eric]

Hi Geert, Philipp,

On 11/04/18 11:15, Geert Uytterhoeven wrote:
> Vfio-platform requires 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,
> 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>
> ---
> 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 b60bb5326668498c..ef9b9e3220ebe939 100644
> --- a/drivers/vfio/platform/vfio_platform_common.c
> +++ b/drivers/vfio/platform/vfio_platform_common.c
> @@ -17,6 +17,7 @@
>  #include <linux/iommu.h>
>  #include <linux/module.h>
>  #include <linux/mutex.h>
> +#include <linux/reset.h>
>  #include <linux/slab.h>
>  #include <linux/types.h>
>  #include <linux/uaccess.h>
> @@ -112,11 +113,13 @@ 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;
>  
> @@ -127,8 +130,16 @@ 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 = of_reset_control_get_exclusive(vdev->device->of_node, NULL);

Shouldn't we prefer the top level reset_control_get_exclusive()?

To make sure about the exclusive/shared terminology, does
get_reset_control_get_exclusive() check we have an exclusive wire
between this device and the reset controller?

Thanks

Eric
> +	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)
> @@ -138,6 +149,8 @@ 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)
> @@ -217,6 +230,9 @@ 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;
>  
>  	/*
> 

Re: [PATCH v3 2/2] vfio: platform: Add generic DT reset support

[Geert Uytterhoeven]

Hi Eric,

On Thu, Apr 12, 2018 at 12:31 PM, Auger Eric <eric.auger@redhat.com> wrote:
> On 11/04/18 11:15, Geert Uytterhoeven wrote:
>> Vfio-platform requires 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,
>> 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>

>> --- a/drivers/vfio/platform/vfio_platform_common.c
>> +++ b/drivers/vfio/platform/vfio_platform_common.c

>> @@ -127,8 +130,16 @@ 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 = of_reset_control_get_exclusive(vdev->device->of_node, NULL);
>
> Shouldn't we prefer the top level reset_control_get_exclusive()?

I guess that should work, too.

> To make sure about the exclusive/shared terminology, does
> get_reset_control_get_exclusive() check we have an exclusive wire
> between this device and the reset controller?

AFAIU, the "exclusive" means that only a single user can obtain access to
the reset, and it does not guarantee that we have an exclusive wire between
the device and the reset controller.

The latter depends on the SoC's reset topology. If a reset wire is shared
by multiple devices (e.g. resets shared by PWM or Display Unit devices on
R-Car SoCs), exporting a subset of these devices to a guest is a bad idea,
indeed.

I guess the same thing can happen with the ACPI "_RST" method?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH v3 2/2] vfio: platform: Add generic DT reset support

[Auger Eric]

Hi Geert,
On 12/04/18 13:32, Geert Uytterhoeven wrote:
> Hi Eric,
> 
> On Thu, Apr 12, 2018 at 12:31 PM, Auger Eric <eric.auger@redhat.com> wrote:
>> On 11/04/18 11:15, Geert Uytterhoeven wrote:
>>> Vfio-platform requires 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,
>>> 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>
> 
>>> --- a/drivers/vfio/platform/vfio_platform_common.c
>>> +++ b/drivers/vfio/platform/vfio_platform_common.c
> 
>>> @@ -127,8 +130,16 @@ 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 = of_reset_control_get_exclusive(vdev->device->of_node, NULL);
>>
>> Shouldn't we prefer the top level reset_control_get_exclusive()?
> 
> I guess that should work, too.
> 
>> To make sure about the exclusive/shared terminology, does
>> get_reset_control_get_exclusive() check we have an exclusive wire
>> between this device and the reset controller?
> 
> AFAIU, the "exclusive" means that only a single user can obtain access to
> the reset, and it does not guarantee that we have an exclusive wire between
> the device and the reset controller.
> 
> The latter depends on the SoC's reset topology. If a reset wire is shared
> by multiple devices (e.g. resets shared by PWM or Display Unit devices on
> R-Car SoCs), exporting a subset of these devices to a guest is a bad idea,
> indeed.

So who's going to check this assigned device will not trigger a reset of
other non assigned devices sharing the same reset controller?

> 
> I guess the same thing can happen with the ACPI "_RST" method?

ACPI spec _RST chapter says about _RST object:

"This object executes a reset on the associated device
 or devices. If included in a device context, the
reset must not affect any other ACPI-described de
vices; if included in a power resource for reset
(_PRR, Section 7.3.26) the reset must affect all ACPI-described devices
that reference it. When this object is described in
a device context, it executes a function level reset that only affects
the device it is associated with; neither parent nor children should be
affected by the execution of this reset. Executing this must only result
in this device resetting without the device appearing as if it
has been removed from the bus altogether, to prevent OSPM re-enumeration
of devices on hot-pluggable buses (e.g. USB)."

Adding Sinan in copy for clarification.

Thanks

Eric
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 

Re: [PATCH v3 2/2] vfio: platform: Add generic DT reset support

[Sinan Kaya]

On 4/12/2018 7:49 AM, Auger Eric wrote:
> Hi Geert,
> On 12/04/18 13:32, Geert Uytterhoeven wrote:
>> Hi Eric,
>>
>> On Thu, Apr 12, 2018 at 12:31 PM, Auger Eric <eric.auger@redhat.com> wrote:
>>> On 11/04/18 11:15, Geert Uytterhoeven wrote:
>>>> Vfio-platform requires 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,
>>>> 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>
>>
>>>> --- a/drivers/vfio/platform/vfio_platform_common.c
>>>> +++ b/drivers/vfio/platform/vfio_platform_common.c
>>
>>>> @@ -127,8 +130,16 @@ 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 = of_reset_control_get_exclusive(vdev->device->of_node, NULL);
>>>
>>> Shouldn't we prefer the top level reset_control_get_exclusive()?
>>
>> I guess that should work, too.
>>
>>> To make sure about the exclusive/shared terminology, does
>>> get_reset_control_get_exclusive() check we have an exclusive wire
>>> between this device and the reset controller?
>>
>> AFAIU, the "exclusive" means that only a single user can obtain access to
>> the reset, and it does not guarantee that we have an exclusive wire between
>> the device and the reset controller.
>>
>> The latter depends on the SoC's reset topology. If a reset wire is shared
>> by multiple devices (e.g. resets shared by PWM or Display Unit devices on
>> R-Car SoCs), exporting a subset of these devices to a guest is a bad idea,
>> indeed.
> 
> So who's going to check this assigned device will not trigger a reset of
> other non assigned devices sharing the same reset controller?

I like the direction in general. I was hoping that you'd call it of_reset_control
rather than reset_control.

Is there anything in the OF spec about what to expect from DT's reset?

> 
>>
>> I guess the same thing can happen with the ACPI "_RST" method?
> 
> ACPI spec _RST chapter says about _RST object:
> 
> "This object executes a reset on the associated device
>  or devices. If included in a device context, the
> reset must not affect any other ACPI-described de
> vices; if included in a power resource for reset
> (_PRR, Section 7.3.26) the reset must affect all ACPI-described devices
> that reference it. When this object is described in
> a device context, it executes a function level reset that only affects
> the device it is associated with; neither parent nor children should be
> affected by the execution of this reset. Executing this must only result
> in this device resetting without the device appearing as if it
> has been removed from the bus altogether, to prevent OSPM re-enumeration
> of devices on hot-pluggable buses (e.g. USB)."

ACPI spec is clear. We are doing a device specific reset aka function level
reset here. It does not impact other devices in the system. 

In fact, ACPI does not have a clock controller concept. All clock/reset details
are hidden from the OS.

> 
> Adding Sinan in copy for clarification.
> 
> Thanks
> 
> Eric
>>
>> Gr{oetje,eeting}s,
>>
>>                         Geert
>>
> 


-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.

Re: [PATCH v3 2/2] vfio: platform: Add generic DT reset support

[Geert Uytterhoeven]

Hi Sinan,

On Thu, Apr 12, 2018 at 2:36 PM, Sinan Kaya <okaya@codeaurora.org> wrote:
> On 4/12/2018 7:49 AM, Auger Eric wrote:
>> On 12/04/18 13:32, Geert Uytterhoeven wrote:
>>> On Thu, Apr 12, 2018 at 12:31 PM, Auger Eric <eric.auger@redhat.com> wrote:
>>>> On 11/04/18 11:15, Geert Uytterhoeven wrote:
>>>>> Vfio-platform requires 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,
>>>>> 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>
>>>
>>>>> --- a/drivers/vfio/platform/vfio_platform_common.c
>>>>> +++ b/drivers/vfio/platform/vfio_platform_common.c
>>>
>>>>> @@ -127,8 +130,16 @@ 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 = of_reset_control_get_exclusive(vdev->device->of_node, NULL);
>>>>
>>>> Shouldn't we prefer the top level reset_control_get_exclusive()?
>>>
>>> I guess that should work, too.
>>>
>>>> To make sure about the exclusive/shared terminology, does
>>>> get_reset_control_get_exclusive() check we have an exclusive wire
>>>> between this device and the reset controller?
>>>
>>> AFAIU, the "exclusive" means that only a single user can obtain access to
>>> the reset, and it does not guarantee that we have an exclusive wire between
>>> the device and the reset controller.
>>>
>>> The latter depends on the SoC's reset topology. If a reset wire is shared
>>> by multiple devices (e.g. resets shared by PWM or Display Unit devices on
>>> R-Car SoCs), exporting a subset of these devices to a guest is a bad idea,
>>> indeed.
>>
>> So who's going to check this assigned device will not trigger a reset of
>> other non assigned devices sharing the same reset controller?
>
> I like the direction in general. I was hoping that you'd call it of_reset_control
> rather than reset_control.

You mean vfio_platform_device.of_reset_control?
If we switch to reset_control_get_exclusive(), that doesn't make much sense...

> Is there anything in the OF spec about what to expect from DT's reset?

Documentation/devicetree/bindings/reset/reset.txt says:

"A word on where to place reset signal consumers in device tree: It is possible
 in hardware for a reset signal to affect multiple logically separate HW blocks
 at once. In this case, it would be unwise to represent this reset signal in
 the DT node of each affected HW block, since if activated, an unrelated block
 may be reset. Instead, reset signals should be represented in the DT node
 where it makes most sense to control it; this may be a bus node if all
 children of the bus are affected by the reset signal, or an individual HW
 block node for dedicated reset signals. The intent of this binding is to give
 appropriate software access to the reset signals in order to manage the HW,
 rather than to slavishly enumerate the reset signal that affects each HW
 block."

So according to the bindings, a specific reset should apply to a single
device only.

A quick check shows there are several violators:

$ for i in $(git grep -lw resets -- "*dts*"); do grep -w resets $i |
sort | uniq -c | sed -e "s@^@$i:@g"; done | grep -v ":      1 "
arch/arm/boot/dts/aspeed-g4.dtsi:     14 resets = <&syscon ASPEED_RESET_I2C>;
arch/arm/boot/dts/aspeed-g5.dtsi:     14 resets = <&syscon ASPEED_RESET_I2C>;
arch/arm/boot/dts/atlas7.dtsi:      2 resets = <&car 29>;
arch/arm/boot/dts/gemini.dtsi:      2 resets = <&syscon GEMINI_RESET_IDE>;
arch/arm/boot/dts/meson8.dtsi:      2 resets = <&reset RESET_USB_OTG>;
arch/arm/boot/dts/meson8b.dtsi:      2 resets = <&reset RESET_USB_OTG>;
arch/arm/boot/dts/r8a7743.dtsi:      7 resets = <&cpg 523>;
arch/arm/boot/dts/r8a7743.dtsi:      2 resets = <&cpg 703>;
arch/arm/boot/dts/r8a7743.dtsi:      2 resets = <&cpg 704>;
arch/arm/boot/dts/r8a7745.dtsi:      7 resets = <&cpg 523>;
arch/arm/boot/dts/r8a7745.dtsi:      2 resets = <&cpg 703>;
arch/arm/boot/dts/r8a7745.dtsi:      2 resets = <&cpg 704>;
arch/arm/boot/dts/r8a7790.dtsi:      3 resets = <&cpg 703>;
arch/arm/boot/dts/r8a7790.dtsi:      2 resets = <&cpg 704>;
arch/arm/boot/dts/r8a7791.dtsi:      2 resets = <&cpg 703>;
arch/arm/boot/dts/r8a7791.dtsi:      2 resets = <&cpg 704>;
arch/arm/boot/dts/r8a7794.dtsi:      2 resets = <&cpg 703>;
arch/arm/boot/dts/r8a7794.dtsi:      2 resets = <&cpg 704>;
arch/arm/boot/dts/stih410.dtsi:      2 resets = <&powerdown
STIH407_USB2_PORT0_POWERDOWN>,
arch/arm/boot/dts/stih410.dtsi:      2 resets = <&powerdown
STIH407_USB2_PORT1_POWERDOWN>,
arch/arm/boot/dts/stih410.dtsi:      2 resets = <&softreset
STIH407_PICOPHY_SOFTRESET>,
arch/arm/boot/dts/stih418.dtsi:      2 resets = <&powerdown
STIH407_USB2_PORT0_POWERDOWN>,
arch/arm/boot/dts/stih418.dtsi:      2 resets = <&powerdown
STIH407_USB2_PORT1_POWERDOWN>,
arch/arm/boot/dts/stih418.dtsi:      2 resets = <&softreset
STIH407_PICOPHY_SOFTRESET>,
arch/arm/boot/dts/sun9i-a80.dtsi:      2 resets = <&de_clocks RST_FE0>;
arch/arm/boot/dts/sun9i-a80.dtsi:      2 resets = <&usb_clocks RST_USB0_HCI>;
arch/arm/boot/dts/sun9i-a80.dtsi:      2 resets = <&usb_clocks RST_USB2_HCI>;
arch/arm/boot/dts/sunxi-h3-h5.dtsi:      2 resets = <&ccu
RST_BUS_EHCI0>, <&ccu RST_BUS_OHCI0>;
arch/arm/boot/dts/sunxi-h3-h5.dtsi:      2 resets = <&ccu
RST_BUS_EHCI1>, <&ccu RST_BUS_OHCI1>;
arch/arm/boot/dts/sunxi-h3-h5.dtsi:      2 resets = <&ccu
RST_BUS_EHCI2>, <&ccu RST_BUS_OHCI2>;
arch/arm/boot/dts/sunxi-h3-h5.dtsi:      2 resets = <&ccu
RST_BUS_EHCI3>, <&ccu RST_BUS_OHCI3>;
arch/arm64/boot/dts/amlogic/meson-gxbb.dtsi:      2 resets = <&reset
RESET_USB_OTG>;
arch/arm64/boot/dts/nvidia/tegra186.dtsi:      2 resets = <&bpmp
TEGRA186_RESET_DSI>;
arch/arm64/boot/dts/renesas/r8a7795.dtsi:      3 resets = <&cpg 328>;
arch/arm64/boot/dts/renesas/r8a7795.dtsi:      7 resets = <&cpg 523>;
arch/arm64/boot/dts/renesas/r8a7795.dtsi:      3 resets = <&cpg 700>;
arch/arm64/boot/dts/renesas/r8a7795.dtsi:      3 resets = <&cpg 701>;
arch/arm64/boot/dts/renesas/r8a7795.dtsi:      3 resets = <&cpg 702>;
arch/arm64/boot/dts/renesas/r8a7795.dtsi:      3 resets = <&cpg 703>;
arch/arm64/boot/dts/renesas/r8a7796.dtsi:      3 resets = <&cpg 328>;
arch/arm64/boot/dts/renesas/r8a7796.dtsi:      7 resets = <&cpg 523>;
arch/arm64/boot/dts/renesas/r8a7796.dtsi:      3 resets = <&cpg 702>;
arch/arm64/boot/dts/renesas/r8a7796.dtsi:      3 resets = <&cpg 703>;
arch/arm64/boot/dts/renesas/r8a77965.dtsi:      3 resets = <&cpg 328>;
arch/arm64/boot/dts/renesas/r8a77965.dtsi:      7 resets = <&cpg 523>;
arch/arm64/boot/dts/renesas/r8a77965.dtsi:      2 resets = <&cpg 702>;
arch/arm64/boot/dts/renesas/r8a77965.dtsi:      4 resets = <&cpg 703>;
arch/arm64/boot/dts/renesas/r8a77995.dtsi:      4 resets = <&cpg 523>;
arch/arm64/boot/dts/renesas/r8a77995.dtsi:      3 resets = <&cpg 703>;
$

Perhaps we should start grouping devices sharing a reset signal in a
"simple-bus" node?

Phillip: any comments?

> ACPI spec is clear. We are doing a device specific reset aka function level
> reset here. It does not impact other devices in the system.

Assumed all ACPI implementations comply, of course.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH v3 2/2] vfio: platform: Add generic DT reset support

[Philipp Zabel]

On Thu, 2018-04-12 at 15:12 +0200, Geert Uytterhoeven wrote:
> Hi Sinan,
> 
> On Thu, Apr 12, 2018 at 2:36 PM, Sinan Kaya <okaya@codeaurora.org> wrote:
> > On 4/12/2018 7:49 AM, Auger Eric wrote:
> > > On 12/04/18 13:32, Geert Uytterhoeven wrote:
> > > > On Thu, Apr 12, 2018 at 12:31 PM, Auger Eric <eric.auger@redhat.com> wrote:
> > > > > On 11/04/18 11:15, Geert Uytterhoeven wrote:
> > > > > > Vfio-platform requires 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,
> > > > > > 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>
> > > > > > --- a/drivers/vfio/platform/vfio_platform_common.c
> > > > > > +++ b/drivers/vfio/platform/vfio_platform_common.c
> > > > > > @@ -127,8 +130,16 @@ 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 = of_reset_control_get_exclusive(vdev->device->of_node, NULL);
> > > > > 
> > > > > Shouldn't we prefer the top level reset_control_get_exclusive()?
> > > > 
> > > > I guess that should work, too.
> > > > 
> > > > > To make sure about the exclusive/shared terminology, does
> > > > > get_reset_control_get_exclusive() check we have an exclusive wire
> > > > > between this device and the reset controller?
> > > > 
> > > > AFAIU, the "exclusive" means that only a single user can obtain access to
> > > > the reset, and it does not guarantee that we have an exclusive wire between
> > > > the device and the reset controller.
> > > > 
> > > > The latter depends on the SoC's reset topology. If a reset wire is shared
> > > > by multiple devices (e.g. resets shared by PWM or Display Unit devices on
> > > > R-Car SoCs), exporting a subset of these devices to a guest is a bad idea,
> > > > indeed.
> > > 
> > > So who's going to check this assigned device will not trigger a reset of
> > > other non assigned devices sharing the same reset controller?

If the reset control is requested as exclusive, any other driver
requesting the same reset control will fail (or this reset_control_get
will fail, whichever comes last).

> > I like the direction in general. I was hoping that you'd call it of_reset_control
> > rather than reset_control.
> 
> You mean vfio_platform_device.of_reset_control?
> If we switch to reset_control_get_exclusive(), that doesn't make much sense...
> 
> > Is there anything in the OF spec about what to expect from DT's reset?
> 
> Documentation/devicetree/bindings/reset/reset.txt says:
> 
> "A word on where to place reset signal consumers in device tree: It is possible
>  in hardware for a reset signal to affect multiple logically separate HW blocks
>  at once. In this case, it would be unwise to represent this reset signal in
>  the DT node of each affected HW block, since if activated, an unrelated block
>  may be reset. Instead, reset signals should be represented in the DT node
>  where it makes most sense to control it; this may be a bus node if all
>  children of the bus are affected by the reset signal, or an individual HW
>  block node for dedicated reset signals. The intent of this binding is to give
>  appropriate software access to the reset signals in order to manage the HW,
>  rather than to slavishly enumerate the reset signal that affects each HW
>  block."

This was written in 2012, and unfortunately the DT binding documentation
does not inform hardware development, and has not been updated since.

There's generally two kinds of reset uses:
- either to bring a device into a known state at a given point in time,
  which is often done using a timed assert/deassert sequence,
- or just to park a device while not in active use (must deassert any
  time before use, may or may not assert any time after use)

For the former case, the above paragraph makes a lot of sense, because
when it is necessary to reset a device that shares the reset line with
another, either choice between disturbing the other device, or not
being able to reset when necessary, is a bad one. The reset controller
framework supports those use cases via the reset_control_get_exclusive
function variants.

But for the latter case, there is absolutely no need to forbid sharing
reset lines among multiple devices, as deassertion/assertion can just be
handled reference counted, like clocks or power management. The reset
controller framework supports those use cases via the
reset_control_get_shared function variants.

The case we are talking about here is the first one.

> So according to the bindings, a specific reset should apply to a single
> device only.

Indeed sharing reset lines between peripherals has become unexpectedly
common, making it impractical to forbid shared resets in the device
tree.

> A quick check shows there are several violators:
> 
> $ for i in $(git grep -lw resets -- "*dts*"); do grep -w resets $i |
> sort | uniq -c | sed -e "s@^@$i:@g"; done | grep -v ":      1 "
> arch/arm/boot/dts/aspeed-g4.dtsi:     14 resets = <&syscon ASPEED_RESET_I2C>;
> arch/arm/boot/dts/aspeed-g5.dtsi:     14 resets = <&syscon ASPEED_RESET_I2C>;
> arch/arm/boot/dts/atlas7.dtsi:      2 resets = <&car 29>;
> arch/arm/boot/dts/gemini.dtsi:      2 resets = <&syscon GEMINI_RESET_IDE>;
> arch/arm/boot/dts/meson8.dtsi:      2 resets = <&reset RESET_USB_OTG>;
> arch/arm/boot/dts/meson8b.dtsi:      2 resets = <&reset RESET_USB_OTG>;
> arch/arm/boot/dts/r8a7743.dtsi:      7 resets = <&cpg 523>;
> arch/arm/boot/dts/r8a7743.dtsi:      2 resets = <&cpg 703>;
> arch/arm/boot/dts/r8a7743.dtsi:      2 resets = <&cpg 704>;
> arch/arm/boot/dts/r8a7745.dtsi:      7 resets = <&cpg 523>;
> arch/arm/boot/dts/r8a7745.dtsi:      2 resets = <&cpg 703>;
> arch/arm/boot/dts/r8a7745.dtsi:      2 resets = <&cpg 704>;
> arch/arm/boot/dts/r8a7790.dtsi:      3 resets = <&cpg 703>;
> arch/arm/boot/dts/r8a7790.dtsi:      2 resets = <&cpg 704>;
> arch/arm/boot/dts/r8a7791.dtsi:      2 resets = <&cpg 703>;
> arch/arm/boot/dts/r8a7791.dtsi:      2 resets = <&cpg 704>;
> arch/arm/boot/dts/r8a7794.dtsi:      2 resets = <&cpg 703>;
> arch/arm/boot/dts/r8a7794.dtsi:      2 resets = <&cpg 704>;
> arch/arm/boot/dts/stih410.dtsi:      2 resets = <&powerdown
> STIH407_USB2_PORT0_POWERDOWN>,
> arch/arm/boot/dts/stih410.dtsi:      2 resets = <&powerdown
> STIH407_USB2_PORT1_POWERDOWN>,
> arch/arm/boot/dts/stih410.dtsi:      2 resets = <&softreset
> STIH407_PICOPHY_SOFTRESET>,
> arch/arm/boot/dts/stih418.dtsi:      2 resets = <&powerdown
> STIH407_USB2_PORT0_POWERDOWN>,
> arch/arm/boot/dts/stih418.dtsi:      2 resets = <&powerdown
> STIH407_USB2_PORT1_POWERDOWN>,
> arch/arm/boot/dts/stih418.dtsi:      2 resets = <&softreset
> STIH407_PICOPHY_SOFTRESET>,
> arch/arm/boot/dts/sun9i-a80.dtsi:      2 resets = <&de_clocks RST_FE0>;
> arch/arm/boot/dts/sun9i-a80.dtsi:      2 resets = <&usb_clocks RST_USB0_HCI>;
> arch/arm/boot/dts/sun9i-a80.dtsi:      2 resets = <&usb_clocks RST_USB2_HCI>;
> arch/arm/boot/dts/sunxi-h3-h5.dtsi:      2 resets = <&ccu
> RST_BUS_EHCI0>, <&ccu RST_BUS_OHCI0>;
> arch/arm/boot/dts/sunxi-h3-h5.dtsi:      2 resets = <&ccu
> RST_BUS_EHCI1>, <&ccu RST_BUS_OHCI1>;
> arch/arm/boot/dts/sunxi-h3-h5.dtsi:      2 resets = <&ccu
> RST_BUS_EHCI2>, <&ccu RST_BUS_OHCI2>;
> arch/arm/boot/dts/sunxi-h3-h5.dtsi:      2 resets = <&ccu
> RST_BUS_EHCI3>, <&ccu RST_BUS_OHCI3>;
> arch/arm64/boot/dts/amlogic/meson-gxbb.dtsi:      2 resets = <&reset
> RESET_USB_OTG>;
> arch/arm64/boot/dts/nvidia/tegra186.dtsi:      2 resets = <&bpmp
> TEGRA186_RESET_DSI>;
> arch/arm64/boot/dts/renesas/r8a7795.dtsi:      3 resets = <&cpg 328>;
> arch/arm64/boot/dts/renesas/r8a7795.dtsi:      7 resets = <&cpg 523>;
> arch/arm64/boot/dts/renesas/r8a7795.dtsi:      3 resets = <&cpg 700>;
> arch/arm64/boot/dts/renesas/r8a7795.dtsi:      3 resets = <&cpg 701>;
> arch/arm64/boot/dts/renesas/r8a7795.dtsi:      3 resets = <&cpg 702>;
> arch/arm64/boot/dts/renesas/r8a7795.dtsi:      3 resets = <&cpg 703>;
> arch/arm64/boot/dts/renesas/r8a7796.dtsi:      3 resets = <&cpg 328>;
> arch/arm64/boot/dts/renesas/r8a7796.dtsi:      7 resets = <&cpg 523>;
> arch/arm64/boot/dts/renesas/r8a7796.dtsi:      3 resets = <&cpg 702>;
> arch/arm64/boot/dts/renesas/r8a7796.dtsi:      3 resets = <&cpg 703>;
> arch/arm64/boot/dts/renesas/r8a77965.dtsi:      3 resets = <&cpg 328>;
> arch/arm64/boot/dts/renesas/r8a77965.dtsi:      7 resets = <&cpg 523>;
> arch/arm64/boot/dts/renesas/r8a77965.dtsi:      2 resets = <&cpg 702>;
> arch/arm64/boot/dts/renesas/r8a77965.dtsi:      4 resets = <&cpg 703>;
> arch/arm64/boot/dts/renesas/r8a77995.dtsi:      4 resets = <&cpg 523>;
> arch/arm64/boot/dts/renesas/r8a77995.dtsi:      3 resets = <&cpg 703>;
> $
> 
> Perhaps we should start grouping devices sharing a reset signal in a
> "simple-bus" node?
> 
> Phillip: any comments?

For some of those it may be possible, but that is basically just a work-
around for reality not matching expectations. There may be other cases
where devices sharing a reset line are not even in the same parent node
because they are controlled via a different bus. In general, I don't
think it is feasible or desirable to force grouping of devices that
share the same reset line into a common parent node.

My suggestion would be to relax the language in the reset.txt DT
bindings doc.

regards
Philipp

Re: [PATCH v3 2/2] vfio: platform: Add generic DT reset support

[Geert Uytterhoeven]

Hi Philipp,

On Thu, Apr 12, 2018 at 4:10 PM, Philipp Zabel <p.zabel@pengutronix.de> wrote:
> On Thu, 2018-04-12 at 15:12 +0200, Geert Uytterhoeven wrote:
>> On Thu, Apr 12, 2018 at 2:36 PM, Sinan Kaya <okaya@codeaurora.org> wrote:
>> > On 4/12/2018 7:49 AM, Auger Eric wrote:
>> > > On 12/04/18 13:32, Geert Uytterhoeven wrote:
>> > > > On Thu, Apr 12, 2018 at 12:31 PM, Auger Eric <eric.auger@redhat.com> wrote:
>> > > > > On 11/04/18 11:15, Geert Uytterhoeven wrote:
>> > > > > > Vfio-platform requires 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,
>> > > > > > 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>
>> > > > > > --- a/drivers/vfio/platform/vfio_platform_common.c
>> > > > > > +++ b/drivers/vfio/platform/vfio_platform_common.c
>> > > > > > @@ -127,8 +130,16 @@ 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 = of_reset_control_get_exclusive(vdev->device->of_node, NULL);
>> > > > >
>> > > > > Shouldn't we prefer the top level reset_control_get_exclusive()?
>> > > >
>> > > > I guess that should work, too.
>> > > >
>> > > > > To make sure about the exclusive/shared terminology, does
>> > > > > get_reset_control_get_exclusive() check we have an exclusive wire
>> > > > > between this device and the reset controller?
>> > > >
>> > > > AFAIU, the "exclusive" means that only a single user can obtain access to
>> > > > the reset, and it does not guarantee that we have an exclusive wire between
>> > > > the device and the reset controller.
>> > > >
>> > > > The latter depends on the SoC's reset topology. If a reset wire is shared
>> > > > by multiple devices (e.g. resets shared by PWM or Display Unit devices on
>> > > > R-Car SoCs), exporting a subset of these devices to a guest is a bad idea,
>> > > > indeed.
>> > >
>> > > So who's going to check this assigned device will not trigger a reset of
>> > > other non assigned devices sharing the same reset controller?
>
> If the reset control is requested as exclusive, any other driver
> requesting the same reset control will fail (or this reset_control_get
> will fail, whichever comes last).
>
>> > I like the direction in general. I was hoping that you'd call it of_reset_control
>> > rather than reset_control.
>>
>> You mean vfio_platform_device.of_reset_control?
>> If we switch to reset_control_get_exclusive(), that doesn't make much sense...
>>
>> > Is there anything in the OF spec about what to expect from DT's reset?
>>
>> Documentation/devicetree/bindings/reset/reset.txt says:
>>
>> "A word on where to place reset signal consumers in device tree: It is possible
>>  in hardware for a reset signal to affect multiple logically separate HW blocks
>>  at once. In this case, it would be unwise to represent this reset signal in
>>  the DT node of each affected HW block, since if activated, an unrelated block
>>  may be reset. Instead, reset signals should be represented in the DT node
>>  where it makes most sense to control it; this may be a bus node if all
>>  children of the bus are affected by the reset signal, or an individual HW
>>  block node for dedicated reset signals. The intent of this binding is to give
>>  appropriate software access to the reset signals in order to manage the HW,
>>  rather than to slavishly enumerate the reset signal that affects each HW
>>  block."
>
> This was written in 2012, and unfortunately the DT binding documentation
> does not inform hardware development, and has not been updated since.
>
> There's generally two kinds of reset uses:
> - either to bring a device into a known state at a given point in time,
>   which is often done using a timed assert/deassert sequence,
> - or just to park a device while not in active use (must deassert any
>   time before use, may or may not assert any time after use)
>
> For the former case, the above paragraph makes a lot of sense, because
> when it is necessary to reset a device that shares the reset line with
> another, either choice between disturbing the other device, or not
> being able to reset when necessary, is a bad one. The reset controller
> framework supports those use cases via the reset_control_get_exclusive
> function variants.
>
> But for the latter case, there is absolutely no need to forbid sharing
> reset lines among multiple devices, as deassertion/assertion can just be
> handled reference counted, like clocks or power management. The reset
> controller framework supports those use cases via the
> reset_control_get_shared function variants.
>
> The case we are talking about here is the first one.

Except that vfio-platform wants to reset the device before and after its
use by the guest, for isolation reasons, which does cause a major
disturbance in case of a shared reset.

>> So according to the bindings, a specific reset should apply to a single
>> device only.
>
> Indeed sharing reset lines between peripherals has become unexpectedly
> common, making it impractical to forbid shared resets in the device
> tree.
>
>> A quick check shows there are several violators:

[...]

>> Perhaps we should start grouping devices sharing a reset signal in a
>> "simple-bus" node?
>>
>> Phillip: any comments?
>
> For some of those it may be possible, but that is basically just a work-
> around for reality not matching expectations. There may be other cases
> where devices sharing a reset line are not even in the same parent node
> because they are controlled via a different bus. In general, I don't
> think it is feasible or desirable to force grouping of devices that
> share the same reset line into a common parent node.

At least for Renesas R-Car SoCs, I think this is feasible, as all affected
devices are currently grouped under the same /soc node.
I added subnodes for all devices sharing resets (one for pwm, 4 for USB2,
and one for USB3; display doesn't have resets yet), and it still boots ;-)

However, ehci_platform_probe() cannot get its (optional) resets anymore.
Probably the reset controller framework needs to be taught to look for
shared resets in the parent node, too?

> My suggestion would be to relax the language in the reset.txt DT
> bindings doc.

Which is fine to keep the status quo with the hardware designers, but makes
it less likely for non-whitelisted generic reset controller support to
become acceptable for the vfio people...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH v3 2/2] vfio: platform: Add generic DT reset support

[Auger Eric]

Hi Geert, Philipp,

On 12/04/18 18:02, Geert Uytterhoeven wrote:
> Hi Philipp,
> 
> On Thu, Apr 12, 2018 at 4:10 PM, Philipp Zabel <p.zabel@pengutronix.de> wrote:
>> On Thu, 2018-04-12 at 15:12 +0200, Geert Uytterhoeven wrote:
>>> On Thu, Apr 12, 2018 at 2:36 PM, Sinan Kaya <okaya@codeaurora.org> wrote:
>>>> On 4/12/2018 7:49 AM, Auger Eric wrote:
>>>>> On 12/04/18 13:32, Geert Uytterhoeven wrote:
>>>>>> On Thu, Apr 12, 2018 at 12:31 PM, Auger Eric <eric.auger@redhat.com> wrote:
>>>>>>> On 11/04/18 11:15, Geert Uytterhoeven wrote:
>>>>>>>> Vfio-platform requires 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,
>>>>>>>> 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>
>>>>>>>> --- a/drivers/vfio/platform/vfio_platform_common.c
>>>>>>>> +++ b/drivers/vfio/platform/vfio_platform_common.c
>>>>>>>> @@ -127,8 +130,16 @@ 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 = of_reset_control_get_exclusive(vdev->device->of_node, NULL);
>>>>>>>
>>>>>>> Shouldn't we prefer the top level reset_control_get_exclusive()?
>>>>>>
>>>>>> I guess that should work, too.
>>>>>>
>>>>>>> To make sure about the exclusive/shared terminology, does
>>>>>>> get_reset_control_get_exclusive() check we have an exclusive wire
>>>>>>> between this device and the reset controller?
>>>>>>
>>>>>> AFAIU, the "exclusive" means that only a single user can obtain access to
>>>>>> the reset, and it does not guarantee that we have an exclusive wire between
>>>>>> the device and the reset controller.
>>>>>>
>>>>>> The latter depends on the SoC's reset topology. If a reset wire is shared
>>>>>> by multiple devices (e.g. resets shared by PWM or Display Unit devices on
>>>>>> R-Car SoCs), exporting a subset of these devices to a guest is a bad idea,
>>>>>> indeed.
>>>>>
>>>>> So who's going to check this assigned device will not trigger a reset of
>>>>> other non assigned devices sharing the same reset controller?
>>
>> If the reset control is requested as exclusive, any other driver
>> requesting the same reset control will fail (or this reset_control_get
>> will fail, whichever comes last).
>>
>>>> I like the direction in general. I was hoping that you'd call it of_reset_control
>>>> rather than reset_control.
>>>
>>> You mean vfio_platform_device.of_reset_control?
>>> If we switch to reset_control_get_exclusive(), that doesn't make much sense...
>>>
>>>> Is there anything in the OF spec about what to expect from DT's reset?
>>>
>>> Documentation/devicetree/bindings/reset/reset.txt says:
>>>
>>> "A word on where to place reset signal consumers in device tree: It is possible
>>>  in hardware for a reset signal to affect multiple logically separate HW blocks
>>>  at once. In this case, it would be unwise to represent this reset signal in
>>>  the DT node of each affected HW block, since if activated, an unrelated block
>>>  may be reset. Instead, reset signals should be represented in the DT node
>>>  where it makes most sense to control it; this may be a bus node if all
>>>  children of the bus are affected by the reset signal, or an individual HW
>>>  block node for dedicated reset signals. The intent of this binding is to give
>>>  appropriate software access to the reset signals in order to manage the HW,
>>>  rather than to slavishly enumerate the reset signal that affects each HW
>>>  block."
>>
>> This was written in 2012, and unfortunately the DT binding documentation
>> does not inform hardware development, and has not been updated since.
>>
>> There's generally two kinds of reset uses:
>> - either to bring a device into a known state at a given point in time,
>>   which is often done using a timed assert/deassert sequence,
>> - or just to park a device while not in active use (must deassert any
>>   time before use, may or may not assert any time after use)
>>
>> For the former case, the above paragraph makes a lot of sense, because
>> when it is necessary to reset a device that shares the reset line with
>> another, either choice between disturbing the other device, or not
>> being able to reset when necessary, is a bad one. The reset controller
>> framework supports those use cases via the reset_control_get_exclusive
>> function variants.
>>
>> But for the latter case, there is absolutely no need to forbid sharing
>> reset lines among multiple devices, as deassertion/assertion can just be
>> handled reference counted, like clocks or power management. The reset
>> controller framework supports those use cases via the
>> reset_control_get_shared function variants.
>>
>> The case we are talking about here is the first one.
> 
> Except that vfio-platform wants to reset the device before and after its
> use by the guest, for isolation reasons, which does cause a major
> disturbance in case of a shared reset.
Do we have any guarantee that drivers whose device are sharing the reset
signal will have got the reset control when the vfio-platform driver
calls reset_control_get_exclusive(). In such a case vfio-platform
reset_control_get_exclusive() will fail and this is what we want.
Otherwise it is unsafe, right. Doesn't this assumption look a little risky?

Thanks

Eric
> 
>>> So according to the bindings, a specific reset should apply to a single
>>> device only.
>>
>> Indeed sharing reset lines between peripherals has become unexpectedly
>> common, making it impractical to forbid shared resets in the device
>> tree.
>>
>>> A quick check shows there are several violators:
> 
> [...]
> 
>>> Perhaps we should start grouping devices sharing a reset signal in a
>>> "simple-bus" node?
>>>
>>> Phillip: any comments?
>>
>> For some of those it may be possible, but that is basically just a work-
>> around for reality not matching expectations. There may be other cases
>> where devices sharing a reset line are not even in the same parent node
>> because they are controlled via a different bus. In general, I don't
>> think it is feasible or desirable to force grouping of devices that
>> share the same reset line into a common parent node.
> 
> At least for Renesas R-Car SoCs, I think this is feasible, as all affected
> devices are currently grouped under the same /soc node.
> I added subnodes for all devices sharing resets (one for pwm, 4 for USB2,
> and one for USB3; display doesn't have resets yet), and it still boots ;-)
> 
> However, ehci_platform_probe() cannot get its (optional) resets anymore.
> Probably the reset controller framework needs to be taught to look for
> shared resets in the parent node, too?
> 
>> My suggestion would be to relax the language in the reset.txt DT
>> bindings doc.
> 
> Which is fine to keep the status quo with the hardware designers, but makes
> it less likely for non-whitelisted generic reset controller support to
> become acceptable for the vfio people...
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 

Re: [PATCH v3 2/2] vfio: platform: Add generic DT reset support

[Geert Uytterhoeven]

Hi Eric,

On Fri, Apr 13, 2018 at 10:52 AM, Auger Eric <eric.auger@redhat.com> wrote:
> On 12/04/18 18:02, Geert Uytterhoeven wrote:
>> On Thu, Apr 12, 2018 at 4:10 PM, Philipp Zabel <p.zabel@pengutronix.de> wrote:
>>> On Thu, 2018-04-12 at 15:12 +0200, Geert Uytterhoeven wrote:
>>>> On Thu, Apr 12, 2018 at 2:36 PM, Sinan Kaya <okaya@codeaurora.org> wrote:
>>>>> On 4/12/2018 7:49 AM, Auger Eric wrote:
>>>>>> On 12/04/18 13:32, Geert Uytterhoeven wrote:
>>>>>>> On Thu, Apr 12, 2018 at 12:31 PM, Auger Eric <eric.auger@redhat.com> wrote:
>>>>>>>> On 11/04/18 11:15, Geert Uytterhoeven wrote:
>>>>>>>>> Vfio-platform requires 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,
>>>>>>>>> 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>
>>>>>>>>> --- a/drivers/vfio/platform/vfio_platform_common.c
>>>>>>>>> +++ b/drivers/vfio/platform/vfio_platform_common.c
>>>>>>>>> @@ -127,8 +130,16 @@ 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 = of_reset_control_get_exclusive(vdev->device->of_node, NULL);
>>>>>>>>
>>>>>>>> Shouldn't we prefer the top level reset_control_get_exclusive()?
>>>>>>>
>>>>>>> I guess that should work, too.
>>>>>>>
>>>>>>>> To make sure about the exclusive/shared terminology, does
>>>>>>>> get_reset_control_get_exclusive() check we have an exclusive wire
>>>>>>>> between this device and the reset controller?
>>>>>>>
>>>>>>> AFAIU, the "exclusive" means that only a single user can obtain access to
>>>>>>> the reset, and it does not guarantee that we have an exclusive wire between
>>>>>>> the device and the reset controller.
>>>>>>>
>>>>>>> The latter depends on the SoC's reset topology. If a reset wire is shared
>>>>>>> by multiple devices (e.g. resets shared by PWM or Display Unit devices on
>>>>>>> R-Car SoCs), exporting a subset of these devices to a guest is a bad idea,
>>>>>>> indeed.
>>>>>>
>>>>>> So who's going to check this assigned device will not trigger a reset of
>>>>>> other non assigned devices sharing the same reset controller?
>>>
>>> If the reset control is requested as exclusive, any other driver
>>> requesting the same reset control will fail (or this reset_control_get
>>> will fail, whichever comes last).
>>>
>>>>> I like the direction in general. I was hoping that you'd call it of_reset_control
>>>>> rather than reset_control.
>>>>
>>>> You mean vfio_platform_device.of_reset_control?
>>>> If we switch to reset_control_get_exclusive(), that doesn't make much sense...
>>>>
>>>>> Is there anything in the OF spec about what to expect from DT's reset?
>>>>
>>>> Documentation/devicetree/bindings/reset/reset.txt says:
>>>>
>>>> "A word on where to place reset signal consumers in device tree: It is possible
>>>>  in hardware for a reset signal to affect multiple logically separate HW blocks
>>>>  at once. In this case, it would be unwise to represent this reset signal in
>>>>  the DT node of each affected HW block, since if activated, an unrelated block
>>>>  may be reset. Instead, reset signals should be represented in the DT node
>>>>  where it makes most sense to control it; this may be a bus node if all
>>>>  children of the bus are affected by the reset signal, or an individual HW
>>>>  block node for dedicated reset signals. The intent of this binding is to give
>>>>  appropriate software access to the reset signals in order to manage the HW,
>>>>  rather than to slavishly enumerate the reset signal that affects each HW
>>>>  block."
>>>
>>> This was written in 2012, and unfortunately the DT binding documentation
>>> does not inform hardware development, and has not been updated since.
>>>
>>> There's generally two kinds of reset uses:
>>> - either to bring a device into a known state at a given point in time,
>>>   which is often done using a timed assert/deassert sequence,
>>> - or just to park a device while not in active use (must deassert any
>>>   time before use, may or may not assert any time after use)
>>>
>>> For the former case, the above paragraph makes a lot of sense, because
>>> when it is necessary to reset a device that shares the reset line with
>>> another, either choice between disturbing the other device, or not
>>> being able to reset when necessary, is a bad one. The reset controller
>>> framework supports those use cases via the reset_control_get_exclusive
>>> function variants.
>>>
>>> But for the latter case, there is absolutely no need to forbid sharing
>>> reset lines among multiple devices, as deassertion/assertion can just be
>>> handled reference counted, like clocks or power management. The reset
>>> controller framework supports those use cases via the
>>> reset_control_get_shared function variants.
>>>
>>> The case we are talking about here is the first one.
>>
>> Except that vfio-platform wants to reset the device before and after its
>> use by the guest, for isolation reasons, which does cause a major
>> disturbance in case of a shared reset.
>
> Do we have any guarantee that drivers whose device are sharing the reset
> signal will have got the reset control when the vfio-platform driver
> calls reset_control_get_exclusive(). In such a case vfio-platform
> reset_control_get_exclusive() will fail and this is what we want.
> Otherwise it is unsafe, right. Doesn't this assumption look a little risky?

No we don't: most drivers don't use reset_control at all.
I think on the Renesas SoCs only USB and Ethernet PHY (which is BTW external,
and thus not covered by the on-SoC reset controller) do.
A few more users may be added in the future.
But all module resets are described in DT.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH v3 2/2] vfio: platform: Add generic DT reset support

[Philipp Zabel]

Hi Geert,

On Thu, 2018-04-12 at 18:02 +0200, Geert Uytterhoeven wrote:
> Hi Philipp,
> 
> On Thu, Apr 12, 2018 at 4:10 PM, Philipp Zabel <p.zabel@pengutronix.de> wrote:
> > On Thu, 2018-04-12 at 15:12 +0200, Geert Uytterhoeven wrote:
> > > On Thu, Apr 12, 2018 at 2:36 PM, Sinan Kaya <okaya@codeaurora.org> wrote:
> > > > On 4/12/2018 7:49 AM, Auger Eric wrote:
> > > > > On 12/04/18 13:32, Geert Uytterhoeven wrote:
> > > > > > On Thu, Apr 12, 2018 at 12:31 PM, Auger Eric <eric.auger@redhat.com> wrote:
> > > > > > > On 11/04/18 11:15, Geert Uytterhoeven wrote:
> > > > > > > > Vfio-platform requires 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,
> > > > > > > > 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>
> > > > > > > > --- a/drivers/vfio/platform/vfio_platform_common.c
> > > > > > > > +++ b/drivers/vfio/platform/vfio_platform_common.c
> > > > > > > > @@ -127,8 +130,16 @@ 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 = of_reset_control_get_exclusive(vdev->device->of_node, NULL);
> > > > > > > 
> > > > > > > Shouldn't we prefer the top level reset_control_get_exclusive()?
> > > > > > 
> > > > > > I guess that should work, too.
> > > > > > 
> > > > > > > To make sure about the exclusive/shared terminology, does
> > > > > > > get_reset_control_get_exclusive() check we have an exclusive wire
> > > > > > > between this device and the reset controller?
> > > > > > 
> > > > > > AFAIU, the "exclusive" means that only a single user can obtain access to
> > > > > > the reset, and it does not guarantee that we have an exclusive wire between
> > > > > > the device and the reset controller.
> > > > > > 
> > > > > > The latter depends on the SoC's reset topology. If a reset wire is shared
> > > > > > by multiple devices (e.g. resets shared by PWM or Display Unit devices on
> > > > > > R-Car SoCs), exporting a subset of these devices to a guest is a bad idea,
> > > > > > indeed.
> > > > > 
> > > > > So who's going to check this assigned device will not trigger a reset of
> > > > > other non assigned devices sharing the same reset controller?
> > 
> > If the reset control is requested as exclusive, any other driver
> > requesting the same reset control will fail (or this reset_control_get
> > will fail, whichever comes last).
> > 
> > > > I like the direction in general. I was hoping that you'd call it of_reset_control
> > > > rather than reset_control.
> > > 
> > > You mean vfio_platform_device.of_reset_control?
> > > If we switch to reset_control_get_exclusive(), that doesn't make much sense...
> > > 
> > > > Is there anything in the OF spec about what to expect from DT's reset?
> > > 
> > > Documentation/devicetree/bindings/reset/reset.txt says:
> > > 
> > > "A word on where to place reset signal consumers in device tree: It is possible
> > >  in hardware for a reset signal to affect multiple logically separate HW blocks
> > >  at once. In this case, it would be unwise to represent this reset signal in
> > >  the DT node of each affected HW block, since if activated, an unrelated block
> > >  may be reset. Instead, reset signals should be represented in the DT node
> > >  where it makes most sense to control it; this may be a bus node if all
> > >  children of the bus are affected by the reset signal, or an individual HW
> > >  block node for dedicated reset signals. The intent of this binding is to give
> > >  appropriate software access to the reset signals in order to manage the HW,
> > >  rather than to slavishly enumerate the reset signal that affects each HW
> > >  block."
> > 
> > This was written in 2012, and unfortunately the DT binding documentation
> > does not inform hardware development, and has not been updated since.
> > 
> > There's generally two kinds of reset uses:
> > - either to bring a device into a known state at a given point in time,
> >   which is often done using a timed assert/deassert sequence,
> > - or just to park a device while not in active use (must deassert any
> >   time before use, may or may not assert any time after use)
> > 
> > For the former case, the above paragraph makes a lot of sense, because
> > when it is necessary to reset a device that shares the reset line with
> > another, either choice between disturbing the other device, or not
> > being able to reset when necessary, is a bad one. The reset controller
> > framework supports those use cases via the reset_control_get_exclusive
> > function variants.
> > 
> > But for the latter case, there is absolutely no need to forbid sharing
> > reset lines among multiple devices, as deassertion/assertion can just be
> > handled reference counted, like clocks or power management. The reset
> > controller framework supports those use cases via the
> > reset_control_get_shared function variants.
> > 
> > The case we are talking about here is the first one.
> 
> Except that vfio-platform wants to reset the device before and after its
> use by the guest, for isolation reasons, which does cause a major
> disturbance in case of a shared reset.

Right. So suddenly we are making devices / drivers that usually would
fall into the latter case add a requirement from the first case.

That also means it is impossible to use just one of the devices that
share a reset line for vfio individually, while the other ones are still
in use by the host. Currently the reset line is a shared resource
similar to the iommu for devices in the same iommu_group.

Is there any mechanism in vfio that would allow modeling other shared
resources apart from iommu?

[...]
> > For some of those it may be possible, but that is basically just a work-
> > around for reality not matching expectations. There may be other cases
> > where devices sharing a reset line are not even in the same parent node
> > because they are controlled via a different bus. In general, I don't
> > think it is feasible or desirable to force grouping of devices that
> > share the same reset line into a common parent node.
> 
> At least for Renesas R-Car SoCs, I think this is feasible, as all affected
> devices are currently grouped under the same /soc node.
> I added subnodes for all devices sharing resets (one for pwm, 4 for USB2,
> and one for USB3; display doesn't have resets yet), and it still boots ;-)

Is this grouping enough to make sure all of the pwm/usb2/usb3 devices
are only ever configured for vfio use together?

Assuming I have pwm[1-4] all sharing the same reset line, and I want
pwm2 to be used by a vfio guest, I first have to make sure that all of
pwm[1-4] are unbound, releasing their shared resets, before vfio-
platform can request the same reset line as exclusive.

Thinking about it, if the pwm drivers keep their requested reset control
around for the duration the device is bound, the reset controller
framework should already kind of handle this - while any of the shared
reset control handles is kept around, any exclusive request for the same
reset control will fail with -EBUSY (and the other way around).
But that requires all drivers to request the reset control during probe
and release it during remove.

> However, ehci_platform_probe() cannot get its (optional) resets anymore.
> Probably the reset controller framework needs to be taught to look for
> shared resets in the parent node, too?

Hm, a generic framework shouldn't do such a thing, the parent node could
be covered by a completely different binding.

> > My suggestion would be to relax the language in the reset.txt DT
> > bindings doc.
> 
> Which is fine to keep the status quo with the hardware designers, but makes
> it less likely for non-whitelisted generic reset controller support to
> become acceptable for the vfio people...

I still may be missing context, but I fail to see how

	pwm@0 {
		resets = <&shared_reset_control>;
	};

	pwm@1 {
		resets = <&shared_reset_control>;
	};

->

	pwms {
		resets = <&shared_reset_control>;

		pwm@0 {
		};

		pwm@1 {
		};
	};

makes any difference here, unless pwms gets bound to an actual driver
that is used for vfio?

regards
Philipp

Re: [PATCH v3 2/2] vfio: platform: Add generic DT reset support

[Auger Eric]

Hi Philipp,

On 13/04/18 11:22, Philipp Zabel wrote:
[..]
> That also means it is impossible to use just one of the devices that
> share a reset line for vfio individually, while the other ones are still
> in use by the host. Currently the reset line is a shared resource
> similar to the iommu for devices in the same iommu_group.
> 
> Is there any mechanism in vfio that would allow modeling other shared
> resources apart from iommu?

No we only check the VFIO group viability at IOMMU level.
> 
> [...]
>>> For some of those it may be possible, but that is basically just a work-
>>> around for reality not matching expectations. There may be other cases
>>> where devices sharing a reset line are not even in the same parent node
>>> because they are controlled via a different bus. In general, I don't
>>> think it is feasible or desirable to force grouping of devices that
>>> share the same reset line into a common parent node.
>>
>> At least for Renesas R-Car SoCs, I think this is feasible, as all affected
>> devices are currently grouped under the same /soc node.
>> I added subnodes for all devices sharing resets (one for pwm, 4 for USB2,
>> and one for USB3; display doesn't have resets yet), and it still boots ;-)
> 
> Is this grouping enough to make sure all of the pwm/usb2/usb3 devices
> are only ever configured for vfio use together?
> 
> Assuming I have pwm[1-4] all sharing the same reset line, and I want
> pwm2 to be used by a vfio guest, I first have to make sure that all of
> pwm[1-4] are unbound, releasing their shared resets, before vfio-
> platform can request the same reset line as exclusive.
> 
> Thinking about it, if the pwm drivers keep their requested reset control
> around for the duration the device is bound, the reset controller
> framework should already kind of handle this - while any of the shared
> reset control handles is kept around, any exclusive request for the same
> reset control will fail with -EBUSY (and the other way around).
> But that requires all drivers to request the reset control during probe
> and release it during remove.
> 
>> However, ehci_platform_probe() cannot get its (optional) resets anymore.
>> Probably the reset controller framework needs to be taught to look for
>> shared resets in the parent node, too?
> 
> Hm, a generic framework shouldn't do such a thing, the parent node could
> be covered by a completely different binding.
> 
>>> My suggestion would be to relax the language in the reset.txt DT
>>> bindings doc.
>>
>> Which is fine to keep the status quo with the hardware designers, but makes
>> it less likely for non-whitelisted generic reset controller support to
>> become acceptable for the vfio people...
> 
> I still may be missing context, but I fail to see how
> 
> 	pwm@0 {
> 		resets = <&shared_reset_control>;
> 	};
> 
> 	pwm@1 {
> 		resets = <&shared_reset_control>;
> 	};
> 
> ->
> 
> 	pwms {
> 		resets = <&shared_reset_control>;
> 
> 		pwm@0 {
> 		};
> 
> 		pwm@1 {
> 		};
> 	};
> 
> makes any difference here, unless pwms gets bound to an actual driver
> that is used for vfio?

I don't think we are ready to assign pwms with VFIO as Alex emphasized
VFIO was meant to be used with IOMMU and I guess those devices do not
belong to any iommu group.

Thanks

Eric
> 
> regards
> Philipp
> 

Re: [PATCH v3 2/2] vfio: platform: Add generic DT reset support

[Geert Uytterhoeven]

Hi Philipp,

On Fri, Apr 13, 2018 at 11:22 AM, Philipp Zabel <p.zabel@pengutronix.de> wrote:
> On Thu, 2018-04-12 at 18:02 +0200, Geert Uytterhoeven wrote:
>> On Thu, Apr 12, 2018 at 4:10 PM, Philipp Zabel <p.zabel@pengutronix.de> wrote:
>> > On Thu, 2018-04-12 at 15:12 +0200, Geert Uytterhoeven wrote:
>> > > On Thu, Apr 12, 2018 at 2:36 PM, Sinan Kaya <okaya@codeaurora.org> wrote:
>> > > > On 4/12/2018 7:49 AM, Auger Eric wrote:
>> > > > > On 12/04/18 13:32, Geert Uytterhoeven wrote:
>> > > > > > On Thu, Apr 12, 2018 at 12:31 PM, Auger Eric <eric.auger@redhat.com> wrote:
>> > > > > > > On 11/04/18 11:15, Geert Uytterhoeven wrote:
>> > > > > > > > Vfio-platform requires 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,
>> > > > > > > > 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>
>> > > > > > > > --- a/drivers/vfio/platform/vfio_platform_common.c
>> > > > > > > > +++ b/drivers/vfio/platform/vfio_platform_common.c
>> > > > > > > > @@ -127,8 +130,16 @@ 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 = of_reset_control_get_exclusive(vdev->device->of_node, NULL);
>> > > > > > >
>> > > > > > > Shouldn't we prefer the top level reset_control_get_exclusive()?
>> > > > > >
>> > > > > > I guess that should work, too.
>> > > > > >
>> > > > > > > To make sure about the exclusive/shared terminology, does
>> > > > > > > get_reset_control_get_exclusive() check we have an exclusive wire
>> > > > > > > between this device and the reset controller?
>> > > > > >
>> > > > > > AFAIU, the "exclusive" means that only a single user can obtain access to
>> > > > > > the reset, and it does not guarantee that we have an exclusive wire between
>> > > > > > the device and the reset controller.
>> > > > > >
>> > > > > > The latter depends on the SoC's reset topology. If a reset wire is shared
>> > > > > > by multiple devices (e.g. resets shared by PWM or Display Unit devices on
>> > > > > > R-Car SoCs), exporting a subset of these devices to a guest is a bad idea,
>> > > > > > indeed.
>> > > > >
>> > > > > So who's going to check this assigned device will not trigger a reset of
>> > > > > other non assigned devices sharing the same reset controller?
>> >
>> > If the reset control is requested as exclusive, any other driver
>> > requesting the same reset control will fail (or this reset_control_get
>> > will fail, whichever comes last).
>> >
>> > > > I like the direction in general. I was hoping that you'd call it of_reset_control
>> > > > rather than reset_control.
>> > >
>> > > You mean vfio_platform_device.of_reset_control?
>> > > If we switch to reset_control_get_exclusive(), that doesn't make much sense...
>> > >
>> > > > Is there anything in the OF spec about what to expect from DT's reset?
>> > >
>> > > Documentation/devicetree/bindings/reset/reset.txt says:
>> > >
>> > > "A word on where to place reset signal consumers in device tree: It is possible
>> > >  in hardware for a reset signal to affect multiple logically separate HW blocks
>> > >  at once. In this case, it would be unwise to represent this reset signal in
>> > >  the DT node of each affected HW block, since if activated, an unrelated block
>> > >  may be reset. Instead, reset signals should be represented in the DT node
>> > >  where it makes most sense to control it; this may be a bus node if all
>> > >  children of the bus are affected by the reset signal, or an individual HW
>> > >  block node for dedicated reset signals. The intent of this binding is to give
>> > >  appropriate software access to the reset signals in order to manage the HW,
>> > >  rather than to slavishly enumerate the reset signal that affects each HW
>> > >  block."
>> >
>> > This was written in 2012, and unfortunately the DT binding documentation
>> > does not inform hardware development, and has not been updated since.
>> >
>> > There's generally two kinds of reset uses:
>> > - either to bring a device into a known state at a given point in time,
>> >   which is often done using a timed assert/deassert sequence,
>> > - or just to park a device while not in active use (must deassert any
>> >   time before use, may or may not assert any time after use)
>> >
>> > For the former case, the above paragraph makes a lot of sense, because
>> > when it is necessary to reset a device that shares the reset line with
>> > another, either choice between disturbing the other device, or not
>> > being able to reset when necessary, is a bad one. The reset controller
>> > framework supports those use cases via the reset_control_get_exclusive
>> > function variants.
>> >
>> > But for the latter case, there is absolutely no need to forbid sharing
>> > reset lines among multiple devices, as deassertion/assertion can just be
>> > handled reference counted, like clocks or power management. The reset
>> > controller framework supports those use cases via the
>> > reset_control_get_shared function variants.
>> >
>> > The case we are talking about here is the first one.
>>
>> Except that vfio-platform wants to reset the device before and after its
>> use by the guest, for isolation reasons, which does cause a major
>> disturbance in case of a shared reset.
>
> Right. So suddenly we are making devices / drivers that usually would
> fall into the latter case add a requirement from the first case.
>
> That also means it is impossible to use just one of the devices that
> share a reset line for vfio individually, while the other ones are still
> in use by the host. Currently the reset line is a shared resource
> similar to the iommu for devices in the same iommu_group.

Correct.

> [...]
>> > For some of those it may be possible, but that is basically just a work-
>> > around for reality not matching expectations. There may be other cases
>> > where devices sharing a reset line are not even in the same parent node
>> > because they are controlled via a different bus. In general, I don't
>> > think it is feasible or desirable to force grouping of devices that
>> > share the same reset line into a common parent node.
>>
>> At least for Renesas R-Car SoCs, I think this is feasible, as all affected
>> devices are currently grouped under the same /soc node.
>> I added subnodes for all devices sharing resets (one for pwm, 4 for USB2,
>> and one for USB3; display doesn't have resets yet), and it still boots ;-)
>
> Is this grouping enough to make sure all of the pwm/usb2/usb3 devices
> are only ever configured for vfio use together?

Currently exporting to a guest using vfio-platform is done on a per-device
basis.

VFIO has to be taught to consider the parent reset, and export them as
a group.

> Assuming I have pwm[1-4] all sharing the same reset line, and I want
> pwm2 to be used by a vfio guest, I first have to make sure that all of
> pwm[1-4] are unbound, releasing their shared resets, before vfio-
> platform can request the same reset line as exclusive.

Right.

> Thinking about it, if the pwm drivers keep their requested reset control
> around for the duration the device is bound, the reset controller
> framework should already kind of handle this - while any of the shared
> reset control handles is kept around, any exclusive request for the same
> reset control will fail with -EBUSY (and the other way around).
> But that requires all drivers to request the reset control during probe
> and release it during remove.

All of that assumes the pwm driver uses resets, which it currently doesn't.

Note that pwm is a bad example, as you probably want to use
para-virtualization instead of vfio-platform.

>> However, ehci_platform_probe() cannot get its (optional) resets anymore.
>> Probably the reset controller framework needs to be taught to look for
>> shared resets in the parent node, too?
>
> Hm, a generic framework shouldn't do such a thing, the parent node could
> be covered by a completely different binding.

True. So grouping is not an option?
Else every single driver needs to be aware of it, and start looking for
parent resets if the device resets cannot be found?

>> > My suggestion would be to relax the language in the reset.txt DT
>> > bindings doc.
>>
>> Which is fine to keep the status quo with the hardware designers, but makes
>> it less likely for non-whitelisted generic reset controller support to
>> become acceptable for the vfio people...
>
> I still may be missing context, but I fail to see how
>
>         pwm@0 {
>                 resets = <&shared_reset_control>;
>         };
>
>         pwm@1 {
>                 resets = <&shared_reset_control>;
>         };
>
> ->
>
>         pwms {
>                 resets = <&shared_reset_control>;
>
>                 pwm@0 {
>                 };
>
>                 pwm@1 {
>                 };
>         };
>
> makes any difference here, unless pwms gets bound to an actual driver
> that is used for vfio?

I just suggested the grouping to comply with the current DT reset bindings,
i.e. to avoid adding the same resets property to multiple nodes.

Doing so has the side effect that even after my patch, a single pwm device
can still not be exported to a guest, as it doesn't have a resets property
anymore.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH] vfio: platform: Fix using devices in PM Domains

[Geert Uytterhoeven]

On Wed, Apr 11, 2018 at 11:15 AM, Geert Uytterhoeven
<geert+renesas@glider.be> wrote:
> If a device is part of a PM Domain (e.g. power and/or clock domain), its
> power state is managed using Runtime PM.  Without Runtime PM, the device
> may not be powered up, causing subtle failures, crashes, or system
> lock-ups when the device is accessed by the guest.
>
> Fix this by adding Runtime PM support, powering the device when the VFIO
> device is opened by the guest.
>
> Note that while more fine-grained power management could be implemented
> on the guest side, if exported, this would be inherently unsafe, as
> abusing it may kill the whole system.
>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

Please ignore, this was sent accidentally with another series.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds