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From:   Heiko Stuebner <heiko@sntech.de>
To:     Mathias Nyman <mathias.nyman@intel.com>,
        Thinh Nguyen <Thinh.Nguyen@synopsys.com>,
        Sam Edwards <cfsworks@gmail.com>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        Sam Edwards <CFSworks@gmail.com>
Subject: Re: [PATCH 1/2] xhci: Introduce "disable-usb3" DT property/quirk
Date:   Tue, 12 Dec 2023 20:31:45 +0100
Message-ID: <4854020.GXAFRqVoOG@phil>
In-Reply-To: <20231208210458.912776-2-CFSworks@gmail.com>
References: <20231208210458.912776-1-CFSworks@gmail.com>
 <20231208210458.912776-2-CFSworks@gmail.com>
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Am Freitag, 8. Dezember 2023, 22:04:57 CET schrieb Sam Edwards:
> Some systems may have xHCI controllers that enumerate USB 3.0 ports, but
> these ports nevertheless cannot be used. Perhaps enabling them triggers a
> hardware bug, or perhaps they simply aren't connected and it would be
> confusing to the user to see an unusable USB 3.0 rhub show up -- whatever
> the case may be, it's reasonable to want to disable these ports.
> 
> Add a DT property (and associated quirk) to the xHCI driver that skips
> over (i.e. ignores and doesn't initialize) any USB 3.0 ports discovered
> during driver initialization.
> 
> Signed-off-by: Sam Edwards <CFSworks@gmail.com>

I'm very much unsure, where the line goes between hw-quirk and
dt-is-not-a-configuration-space - in this specific instance.

DT is meant to describe the actual hardware present and not how
any operating system supports it.

So having that usb3phy present in the kernel - even if only in
a more limited form as you describe would be my preference.


But for a short-term thing, the usb3-phy in the binding is optional, so
so you could "just" deduce the no-usb3 state in your code from its
absence from the dt-node?


Heiko


>  Documentation/devicetree/bindings/usb/usb-xhci.yaml | 4 ++++
>  drivers/usb/host/xhci-mem.c                         | 4 ++++
>  drivers/usb/host/xhci-plat.c                        | 3 +++
>  drivers/usb/host/xhci.h                             | 1 +
>  4 files changed, 12 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/usb/usb-xhci.yaml b/Documentation/devicetree/bindings/usb/usb-xhci.yaml
> index 180a261c3e8f..8a64e747260a 100644
> --- a/Documentation/devicetree/bindings/usb/usb-xhci.yaml
> +++ b/Documentation/devicetree/bindings/usb/usb-xhci.yaml
> @@ -25,6 +25,10 @@ properties:
>      description: Set if the controller has broken port disable mechanism
>      type: boolean
>  
> +  disable-usb3:
> +    description: Ignore (don't initialize, don't use) USB3 ports
> +    type: boolean
> +
>    imod-interval-ns:
>      description: Interrupt moderation interval
>      default: 5000
> diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
> index 0a37f0d511cf..bf8fcab626e4 100644
> --- a/drivers/usb/host/xhci-mem.c
> +++ b/drivers/usb/host/xhci-mem.c
> @@ -1968,6 +1968,10 @@ static void xhci_add_in_port(struct xhci_hcd *xhci, unsigned int num_ports,
>  	minor_revision = XHCI_EXT_PORT_MINOR(temp);
>  
>  	if (major_revision == 0x03) {
> +		/* Ignore USB3 ports entirely if USB3 support is disabled. */
> +		if (xhci->quirks & XHCI_DISABLE_USB3)
> +			return;
> +
>  		rhub = &xhci->usb3_rhub;
>  		/*
>  		 * Some hosts incorrectly use sub-minor version for minor
> diff --git a/drivers/usb/host/xhci-plat.c b/drivers/usb/host/xhci-plat.c
> index b93161374293..75285fb5bbbc 100644
> --- a/drivers/usb/host/xhci-plat.c
> +++ b/drivers/usb/host/xhci-plat.c
> @@ -249,6 +249,9 @@ int xhci_plat_probe(struct platform_device *pdev, struct device *sysdev, const s
>  		if (device_property_read_bool(tmpdev, "quirk-broken-port-ped"))
>  			xhci->quirks |= XHCI_BROKEN_PORT_PED;
>  
> +		if (device_property_read_bool(tmpdev, "disable-usb3"))
> +			xhci->quirks |= XHCI_DISABLE_USB3;
> +
>  		device_property_read_u32(tmpdev, "imod-interval-ns",
>  					 &xhci->imod_interval);
>  	}
> diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
> index 5df370482521..c53fbeea478f 100644
> --- a/drivers/usb/host/xhci.h
> +++ b/drivers/usb/host/xhci.h
> @@ -1906,6 +1906,7 @@ struct xhci_hcd {
>  #define XHCI_RESET_TO_DEFAULT	BIT_ULL(44)
>  #define XHCI_ZHAOXIN_TRB_FETCH	BIT_ULL(45)
>  #define XHCI_ZHAOXIN_HOST	BIT_ULL(46)
> +#define XHCI_DISABLE_USB3	BIT_ULL(47)
>  
>  	unsigned int		num_active_eps;
>  	unsigned int		limit_active_eps;
>