From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alex Williamson Subject: Re: [PATCH/RFC v4 2/2] vfio: platform: Add generic reset controller support Date: Wed, 19 Sep 2018 12:19:37 -0600 Message-ID: <20180919121937.4c7fac9c@t450s.home> References: <20180917163955.19023-1-geert+renesas@glider.be> <20180917163955.19023-3-geert+renesas@glider.be> <9dc74e23-2f57-7db3-6fb6-4f75ed61575f@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <9dc74e23-2f57-7db3-6fb6-4f75ed61575f@redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: Auger Eric Cc: Geert Uytterhoeven , Geert Uytterhoeven , Philipp Zabel , KVM list , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , Linux-Renesas , Linux Kernel Mailing List List-Id: devicetree@vger.kernel.org On Wed, 19 Sep 2018 17:31:43 +0200 Auger Eric wrote: > 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 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 > >>> Reviewed-by: Philipp Zabel > >>> Reviewed-by: Simon Horman > > > >>> --- 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? Yeah, I don't see that one errno vs another really matters in the grand scheme of things. I also don't see that propagating this particular errno adds much value, but it is good general practice, so seems ok to me unless there are other concerns. Thanks, Alex