linux-kernel - Re: [PATCH 2/2] vfio: platform: Add generic DT reset support

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Date:   Wed, 21 Feb 2018 17:51:00 +0100
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Baptiste Reynal <b.reynal@...tualopensystems.com>,
        Alex Williamson <alex.williamson@...hat.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>, kvm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] vfio: platform: Add generic DT reset support

Hi Geert,

I have a suggestion to avoid having to use the IS_ERR_OR_NULL macro, see
below:

On Tue, 2018-02-13 at 17:36 +0100, 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,
> and can be reset in a generic way.  Hence add support to reset such
> devices using the reset controller subsystem, provided the reset
> hierarchy is described correctly in DT using the "resets" property.
> 
> Devices that 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 if reset controller support is disabled.
> 
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
>  drivers/vfio/platform/vfio_platform_common.c  | 23 +++++++++++++++++++++--
>  drivers/vfio/platform/vfio_platform_private.h |  1 +
>  2 files changed, 22 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/vfio/platform/vfio_platform_common.c b/drivers/vfio/platform/vfio_platform_common.c
> index b60bb5326668498c..5d1e48f96e423508 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>
> @@ -112,7 +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;
> +	if (vdev->of_reset)
> +		return true;
> +
> +	if (!IS_ERR_OR_NULL(vdev->reset_control))
> +		return true;

I'd avoid storing error values in vdev->reset_control at all, so this
could be:

	if (vdev->reset_control)
		return true;

> +
> +	return false;
>  }
>  
>  static int vfio_platform_get_reset(struct vfio_platform_device *vdev)
> @@ -127,8 +134,15 @@ 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;
> +
> +	vdev->reset_control = __of_reset_control_get(vdev->device->of_node,
> +						     NULL, 0, false, false);
> +	if (!IS_ERR(vdev->reset_control))
> +		return 0;

if you assign to a local variable first here:

	struct reset_control *rstc;

	 ...

	rstc = of_reset_control_get_exclusive(vdev->device->of_node, NULL);
	if (!IS_ERR(rstc)) {
		vdev->reset_control = rstc;
		return 0;
	}

Also, please don't use __of_reset_control_get directly.

>  
> -	return vdev->of_reset ? 0 : -ENOENT;
> +	return PTR_ERR(vdev->reset_control);

	return PTR_ERR(rstc);

>  }
>  
>  static void vfio_platform_put_reset(struct vfio_platform_device *vdev)
> @@ -138,6 +152,8 @@ 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 +233,9 @@ 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 (!IS_ERR_OR_NULL(vdev->reset_control)) {
> +		dev_info(vdev->device, "reset\n");
> +		return reset_control_reset(vdev->reset_control);

	} 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;
>  
>  	/*

regards
Philipp