Re: [PATCH 2/2] usb: dwc3: host: Disable USB3 ports if maximum-speed doesn't permit USB3 - Greg Kroah-Hartman

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Sam Edwards <cfsworks@gmail.com>
Cc: Mathias Nyman <mathias.nyman@intel.com>,
	Thinh Nguyen <Thinh.Nguyen@synopsys.com>,
	Heiko Stuebner <heiko@sntech.de>,
	linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] usb: dwc3: host: Disable USB3 ports if maximum-speed doesn't permit USB3
Date: Fri, 15 Dec 2023 13:44:17 +0100	[thread overview]
Message-ID: <2023121506-persecute-lining-45bf@gregkh> (raw)
In-Reply-To: <20231208210458.912776-3-CFSworks@gmail.com>

On Fri, Dec 08, 2023 at 02:04:58PM -0700, Sam Edwards wrote:
> The DWC3 core can be configured (during IP instantiation, and/or via
> configuration signals) not to have any USB3 ports. Some SoCs, however,
> may have USB3 interfaces enabled that do not have USB3 PHYs driving
> them. This can be due to a few circumstances, including:
> a) The hardware designer didn't include USB3 PHYs and neglected to
>    disable the DWC3 core's USB ports (I know of no instance where this
>    has actually happened, however, and it seems pretty unlikely).
> b) The USB3 PHYs are present but powered off. Perhaps a driver to enable
>    the PHYs has not yet been written or merged, or USB3 capability is
>    unneeded in the system and the system designer would like to conserve
>    power.
> c) The USB3 PHYs are muxed to a different controller. This can happen if
>    the PHYs support non-USB protocols and one of these alternate
>    functions is needed instead.
> 
> In these circumstances, if the DWC3 does not receive clear link status
> indication on an enabled USB3 port, the DWC3 may not allow even USB2
> to function: in host mode, the DWC3 generates an endless barrage of
> PORT_CSC status on the accompanying USB2 port, and the xHCI driver is
> unable to bring the USB2 port to a functioning state.
> 
> Fix this by first checking if the maximum-speed property in the DT
> permits USB3. If not, pass the new `disable-usb3;` property to the
> virtual xHCI device, causing the xHCI driver not to enable the USB3
> ports. This allows USB2 to function even with USB3 PHYs
> missing/misbehaving, and may be useful even when the USB3 PHYs are
> well-behaved: a DT author may know that USB3 support is intact, but
> disconnected (not exposed off-board) and choose to lower the
> maximum-speed property to avoid an unusable USB3 rhub showing up in
> sysfs/lsusb where it may mislead end-users.
> 
> Signed-off-by: Sam Edwards <CFSworks@gmail.com>
> ---
>  drivers/usb/dwc3/host.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)

Where is patch 1/2 of this series?

confused,

greg k-h