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

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Message-ID: <CAK8P3a0F4sK=ou8HXmSktq+0S22juYaCaY48RStDKwk8QGgviQ@mail.gmail.com>
Date:   Wed, 10 Jan 2018 21:57:17 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Kishon Vijay Abraham I <kishon@...com>
Cc:     Eric Anholt <eric@...olt.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        DTML <devicetree@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Rob Herring <robh+dt@...nel.org>, linux-usb@...r.kernel.org,
        "# 3.4.x" <stable@...r.kernel.org>,
        Stefan Wahren <stefan.wahren@...e.com>,
        Felipe Balbi <balbi@...nel.org>,
        Andrzej Pietrasiewicz <andrzej.p@...sung.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] phy: work around 'phys' references to usb-phy devices

On Mon, Jan 8, 2018 at 7:32 PM, Kishon Vijay Abraham I <kishon@...com> wrote:
> Hi Arnd,
>
> On Monday 08 January 2018 06:31 PM, Arnd Bergmann 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, usb_add_hcd() (along with the respective functions in dwc2 and
>> dwc3) propagate the EPROBE_DEFER return code so we can try again whenever
>> the driver gets loaded. In case the driver is written for the usb-phy
>> subsystem (like usb-generic-phy aka usb-nop-xceiv), we will never load
>> a generic-phy driver for it, and keep failing here.
>>
>> There is only a small number of remaining usb-phy drivers that support
>> device tree, so this adds a workaround by providing a full list of the
>> potentially affected drivers, and always failing the probe with -ENODEV
>> here, which is the same behavior that we used to get with incorrect
>> device tree files. 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).
>> Reverting back to the DTS sources that work would in theory fix USB
>> support for now, but in the long run we'd run into the same problem
>> again when the drivers get ported from usb-phy to generic-phy.
>>
>> Fixes: 014d6da6cb25 ("ARM: dts: bcm283x: Fix DTC warnings about missing phy-cells")
>> Link: https://marc.info/?l=linux-usb&m=151518314314753&w=2
>> Cc: stable@...r.kernel.org
>> Cc: Stefan Wahren <stefan.wahren@...e.com>
>> Cc: Felipe Balbi <balbi@...nel.org>
>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>> ---
>> This obviously needs to be tested, I wrote this up as a reply to
>> Stefan's bug report. I'm fairly sure that I covered all usb-phy
>> driver strings here. My goal is to have a fix merged into 4.15
>> rather than reverting all the DT fixes.
>
> Shouldn't the fix be in phy consumer drivers to not return error if it's able
> to find the phy either using usb-phy or generic phy?

Stefan has posted a patch to that effect now, but I fear that might be
a little fragile, in particular this short before the release with the
regression
in place.

The main problem is that we'd have to change the generic
usb_add_hcd() function in addition to dwc2 and dwc3 to ignore
-EPROBE_DEFER from phy_get() whenever usb_get_phy_dev()
has already succeeded.

If there is any HCD that relies on usb_add_hcd() to get both the
usb_phy and the phy structures, and it may need to defer probing
when the latter one isn't ready yet, that fix would break another
driver.

>> diff --git a/drivers/phy/phy-core.c b/drivers/phy/phy-core.c
>> index b4964b067aec..bb4dd2a2de2d 100644
>> --- a/drivers/phy/phy-core.c
>> +++ b/drivers/phy/phy-core.c
>> @@ -387,6 +387,24 @@ int phy_calibrate(struct phy *phy)
>>  }
>>  EXPORT_SYMBOL_GPL(phy_calibrate);
>>
>> +static struct of_device_id __maybe_unused legacy_usbphy[] = {
>> +     { .compatible = "fsl,imx23-usbphy" },
>> +     { .compatible = "fsl,imx6q-usbphy" },
>> +     { .compatible = "fsl,imx6sl-usbphy" },
>> +     { .compatible = "fsl,imx6sx-usbphy" },
>> +     { .compatible = "fsl,imx6ul-usbphy" },
>> +     { .compatible = "fsl,vf610-usbphy" },
>> +     { .compatible = "nvidia,tegra20-usb-phy" },
>> +     { .compatible = "nvidia,tegra30-usb-phy" },
>> +     { .compatible = "nxp,isp1301" },
>> +     { .compatible = "ti,am335x-usb-ctrl-module" },
>> +     { .compatible = "ti,am335x-usb-phy" },
>> +     { .compatible = "ti,keystone-usbphy" },
>> +     { .compatible = "ti,twl6030-usb" },
>> +     { .compatible = "usb-nop-xceiv" },
>> +     {},
>
> "ti,am335x-usb-ctrl-module" and "ti,twl6030-usb" are not phys.

Ok, I see.

       Arnd