linux-kernel - Re: [PATCH] phy: work around 'phys' references to usb-nop-xceiv devices

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Date:   Fri, 12 Jan 2018 13:54:32 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        Florian Fainelli <f.fainelli@...il.com>,
        John Youn <johnyoun@...opsys.com>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "moderated list:BROADCOM BCM2835 ARM ARCHITECTURE" 
        <linux-rpi-kernel@...ts.infradead.org>,
        stable <stable@...r.kernel.org>,
        Stefan Wahren <stefan.wahren@...e.com>,
        Felipe Balbi <balbi@...nel.org>, Eric Anholt <eric@...olt.net>,
        Andrzej Pietrasiewicz <andrzej.p@...sung.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] phy: work around 'phys' references to usb-nop-xceiv devices

On Fri, Jan 12, 2018 at 4:12 AM, Arnd Bergmann <arnd@...db.de> wrote:
> Stefan Wahren reports a problem with a warning fix that was merged
> for v4.15: we had lots of device nodes with a 'phys' property pointing
> to a device node that is not compliant with the binding documented in
> Documentation/devicetree/bindings/phy/phy-bindings.txt
>
> This generally works because USB HCD drivers that support both the generic
> phy subsystem and the older usb-phy subsystem ignore most errors from
> phy_get() and related calls and then use the usb-phy driver instead.
>
> However, it turns out that making the usb-nop-xceiv device compatible with
> the generic-phy binding changes the phy_get() return code from -EINVAL to
> -EPROBE_DEFER, and the dwc2 usb controller driver for bcm2835 now returns
> -EPROBE_DEFER from its probe function rather than ignoring the failure,
> breaking all USB support on raspberry-pi when CONFIG_GENERIC_PHY is
> enabled. The same code is used in the dwc3 driver and the usb_add_hcd()
> function, so a reasonable assumption would be that many other platforms
> are affected as well.
>
> I have reviewed all the related patches and concluded that "usb-nop-xceiv"
> is the only USB phy that is affected by the change, and since it is by far
> the most commonly referenced phy, all the other USB phy drivers appear
> to be used in ways that are are either safe in DT (they don't use the
> 'phys' property), or in the driver (they already ignore -EPROBE_DEFER
> from generic-phy when usb-phy is available).
>
> To work around the problem, this adds a special case to _of_phy_get()
> so we ignore any PHY node that is compatible with "usb-nop-xceiv",
> as we know that this can never load no matter how much we defer. In the
> future, we might implement a generic-phy driver for "usb-nop-xceiv"
> and then remove this workaround.
>
> Since we generally want older kernels to also want to work with the
> fixed devicetree files, it would be good to backport the patch into
> stable kernels as well (3.13+ are possibly affected), even though they
> don't contain any of the patches that may have caused regressions.
>
> Fixes: 014d6da6cb25 ARM: dts: bcm283x: Fix DTC warnings about missing phy-cells
> Fixes: c5bbf358b790 arm: dts: nspire: Add missing #phy-cells to usb-nop-xceiv
> Fixes: 44e5dced2ef6 arm: dts: marvell: Add missing #phy-cells to usb-nop-xceiv
> Fixes: f568f6f554b8 ARM: dts: omap: Add missing #phy-cells to usb-nop-xceiv
> Fixes: d745d5f277bf ARM: dts: imx51-zii-rdu1: Add missing #phy-cells to usb-nop-xceiv
> Fixes: 915fbe59cbf2 ARM: dts: imx: Add missing #phy-cells to usb-nop-xceiv
> Link: https://marc.info/?l=linux-usb&m=151518314314753&w=2
> Link: https://patchwork.kernel.org/patch/10158145/
> Cc: stable@...r.kernel.org
> Cc: Stefan Wahren <stefan.wahren@...e.com>
> Cc: Felipe Balbi <balbi@...nel.org>
> Cc: Eric Anholt <eric@...olt.net>
> Tested-by: Hans Verkuil <hans.verkuil@...co.com>
> Acked-by: Kishon Vijay Abraham I <kishon@...com>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> Hans tested the earlier version of this patch, I'd like one more
> confirmation from Hans or Stefan (or anyone else) that this version
> addresses the regression as well before this gets merged.
>
> Greg, can you pick this up into usb-linus for v4.15 once the fix
> has been confirmed, or should I merge it through arm-soc?
> ---
>  drivers/phy/phy-core.c | 4 ++++
>  1 file changed, 4 insertions(+)

Thanks for fixing this.

Acked-by: Rob Herring <robh@...nel.org>

Rob