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

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Date:   Wed, 11 Apr 2018 10:43:14 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Philipp Zabel <p.zabel@...gutronix.de>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Baptiste Reynal <b.reynal@...tualopensystems.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        KVM list <kvm@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] vfio: platform: Add generic DT reset controller support

Hi Philipp,

On Wed, Apr 11, 2018 at 10:22 AM, Philipp Zabel <p.zabel@...gutronix.de> wrote:
> 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>

Thanks!

>> --- 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.

Not really. The single caller (vfio_platform_probe_common()) already returns
-EINVAL if no IOMMU group is found, so this should be handled fine.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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