linux-kernel - Re: [PATCH v2 2/2] vfio: platform: Add generic DT reset controller support

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Message-ID: <1523434945.4739.1.camel@pengutronix.de>
Date:   Wed, 11 Apr 2018 10:22:25 +0200
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 v2 2/2] vfio: platform: Add generic DT reset controller
 support

On Tue, 2018-04-10 at 17:53 +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@...der.be>

Reviewed-by: Philipp Zabel <p.zabel@...gutronix.de>

> ---
> 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  | 26 ++++++++++++++++++++++++--
>  drivers/vfio/platform/vfio_platform_private.h |  1 +
>  2 files changed, 25 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/vfio/platform/vfio_platform_common.c b/drivers/vfio/platform/vfio_platform_common.c
> index b60bb5326668498c..3c13327b2777f8ec 100644
> --- a/drivers/vfio/platform/vfio_platform_common.c
> +++ b/drivers/vfio/platform/vfio_platform_common.c
[...]
> @@ -127,8 +136,16 @@ 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 vdev->device->of_node == NULL, this will return -EINVAL ...

> +	if (!IS_ERR(rstc)) {
> +		vdev->reset_control = rstc;
> +		return 0;
> +	}
>  
> -	return vdev->of_reset ? 0 : -ENOENT;
> +	return PTR_ERR(rstc);

... instead of -ENOENT, if that makes any difference.

regards
Philipp