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

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Message-ID: <aa02104b-d80d-8b12-4403-b5cedc23f03a@ti.com>
Date:   Tue, 9 Jan 2018 00:02:54 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     Eric Anholt <eric@...olt.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        Rob Herring <robh+dt@...nel.org>, <linux-usb@...r.kernel.org>,
        <stable@...r.kernel.org>, Stefan Wahren <stefan.wahren@...e.com>,
        Felipe Balbi <balbi@...nel.org>,
        Andrzej Pietrasiewicz <andrzej.p@...sung.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] phy: work around 'phys' references to usb-phy devices

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?
> ---
>  drivers/phy/phy-core.c | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> 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.

Thanks
Kishon