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SubjectRe: [PATCH/RFC v4 2/2] vfio: platform: Add generic reset controller support
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Hi Geert,

On 9/19/18 2:54 PM, Geert Uytterhoeven wrote:
> Hi Eric,
>
> On Wed, Sep 19, 2018 at 2:36 PM Auger Eric <eric.auger@redhat.com> wrote:
>> On 9/17/18 6:39 PM, Geert Uytterhoeven wrote:
>>> Vfio-platform requires dedicated reset support, provided either by ACPI,
>>> or, on DT platforms, by a device-specific reset driver matching against
>>> the device's compatible value.
>>>
>>> On many SoCs, devices are connected to an SoC-internal reset controller.
>>> If the reset hierarchy is described in DT using "resets" properties, or
>>> in lookup tables in platform code, such devices can be reset in a
>>> generic way through the reset controller subsystem. Hence add support
>>> for this, avoiding the need to write device-specific reset drivers for
>>> each single device on affected SoCs.
>>>
>>> Devices that do require a more complex reset procedure can still provide
>>> a device-specific reset driver, as that takes precedence.
>>>
>>> Note that this functionality depends on CONFIG_RESET_CONTROLLER=y, and
>>> becomes a no-op (as in: "No reset function found for device") if reset
>>> controller support is disabled.
>>>
>>> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
>>> Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
>>> Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
>
>>> --- a/drivers/vfio/platform/vfio_platform_common.c
>>> +++ b/drivers/vfio/platform/vfio_platform_common.c
>
>>> @@ -128,8 +131,16 @@ static int vfio_platform_get_reset(struct vfio_platform_device *vdev)
>>> vdev->of_reset = vfio_platform_lookup_reset(vdev->compat,
>>> &vdev->reset_module);
>>> }
>>> + if (vdev->of_reset)
>>> + return 0;
>>> +
>>> + rstc = reset_control_get_dedicated(vdev->device, NULL);
>>> + if (!IS_ERR(rstc)) {
>>> + vdev->reset_control = rstc;
>>> + return 0;
>>> + }
>>>
>>> - return vdev->of_reset ? 0 : -ENOENT;
>>> + return PTR_ERR(rstc);
>> This changes the returned value as seen by the user (probe returned
>> valud). Can we keep -ENOENT in case of no reset controller found?
>
> On success, it still returns 0.
> On failure, it forwards the error from reset_control_get_dedicated(), which
> is IMHO better than replacing it by -ENOENT: we try to propagate error
> codes as much as possible. It could e.g. return -EPROBE_DEFER.
>
> Is there anything that relies on the function returning -ENOENT?
None I am aware of actually. I was afraid about compatibility break but
here we would change an errno by another one so maybe that's not a big
deal at that stage of vfio_platform usage?

Thanks

Eric
>
>> Otherwise looks good to me with the new "dedicated" reset semantics.
>
> Thanks!
>
> Gr{oetje,eeting}s,
>
> Geert
>

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