Hi Eric,

On Wed, Sep 19, 2018 at 2:36 PM Auger Eric [off-list ref] wrote:

On 9/17/18 6:39 PM, Geert Uytterhoeven wrote:

quoted

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 <redacted>

quoted

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

quoted

@@ -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?

Otherwise looks good to me with the new "dedicated" reset semantics.

Thanks!

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