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Subject: Re: [RFC PATCH] USB:XHCI:Modify XHCI driver for USB2.0 controller
To:     Longfang Liu <liulongfang@huawei.com>, gregkh@linuxfoundation.org,
        mathias.nyman@intel.com
Cc:     linux-usb@vger.kernel.org, yisen.zhuang@huawei.com,
        linux-kernel@vger.kernel.org
References: <1614327697-1021-1-git-send-email-liulongfang@huawei.com>
From:   Mathias Nyman <mathias.nyman@linux.intel.com>
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Message-ID: <127e3e5c-f485-64dd-235c-1971d6cd9a4a@linux.intel.com>
Date:   Fri, 26 Feb 2021 11:22:17 +0200
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In-Reply-To: <1614327697-1021-1-git-send-email-liulongfang@huawei.com>
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Precedence: bulk

On 26.2.2021 10.21, Longfang Liu wrote:
> Our current XHCI hardware controller has been customized to only
> support USB 2.0 ports. When using the current xhci driver, an xhci
> controller device and an ehci controller device will be created
> automatically. We want the driver to create only one ehci controller.
> After modifying the driver as follows, an error will occur.
> Is there any other modification method?

The xhci driver relies on the existence of both a main and a shared hcd.
One hcd for handing USB 2 (and slower) and the other for USB 3 devices.

As one example xhci_run(hcd) needs to be called for both hcds, first call
sets up things, second one calls xhci_start() that makes the controller run.

It's probably possible to modify the driver to support xHCI hosts with only
USB 2 ports, but requires a lot more work.

> 
> Signed-off-by: Longfang Liu <liulongfang@huawei.com>
> ---
>  drivers/usb/host/xhci-pci.c | 15 ++-------------
>  1 file changed, 2 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/usb/host/xhci-pci.c b/drivers/usb/host/xhci-pci.c
> index ef513c2..7296aad 100644
> --- a/drivers/usb/host/xhci-pci.c
> +++ b/drivers/usb/host/xhci-pci.c
> @@ -364,26 +364,15 @@ static int xhci_pci_probe(struct pci_dev *dev, const struct pci_device_id *id)
>  	/* USB 2.0 roothub is stored in the PCI device now. */
>  	hcd = dev_get_drvdata(&dev->dev);
>  	xhci = hcd_to_xhci(hcd);
> -	xhci->shared_hcd = usb_create_shared_hcd(&xhci_pci_hc_driver, &dev->dev,
> -						 pci_name(dev), hcd);
> -	if (!xhci->shared_hcd) {
> -		retval = -ENOMEM;
> -		goto dealloc_usb2_hcd;
> -	}
> -
> +	xhci->shared_hcd = NULL;
>  	retval = xhci_ext_cap_init(xhci);
>  	if (retval)
>  		goto put_usb3_hcd;
>  
> -	retval = usb_add_hcd(xhci->shared_hcd, dev->irq,
> +	retval = usb_add_hcd(xhci->main_hcd, dev->irq,
>  			IRQF_SHARED);
>  	if (retval)
>  		goto put_usb3_hcd;
> -	/* Roothub already marked as USB 3.0 speed */
> -
> -	if (!(xhci->quirks & XHCI_BROKEN_STREAMS) &&
> -			HCC_MAX_PSA(xhci->hcc_params) >= 4)
> -		xhci->shared_hcd->can_do_streams = 1;
>  
>  	/* USB-2 and USB-3 roothubs initialized, allow runtime pm suspend */
>  	pm_runtime_put_noidle(&dev->dev);
> 

Something like the above could of course not be accepted upstream. We can't break existing
functionality to support one modified xHCI.

Thanks
Mathias