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Subject: Re: [RFC PATCH] USB:XHCI:Modify XHCI driver for USB2.0 controller
To:     Mathias Nyman <mathias.nyman@linux.intel.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>
 <127e3e5c-f485-64dd-235c-1971d6cd9a4a@linux.intel.com>
From:   liulongfang <liulongfang@huawei.com>
Message-ID: <82be4215-8037-6aab-1d25-92bcca410af4@huawei.com>
Date:   Sat, 27 Feb 2021 11:34:25 +0800
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On 2021/2/26 17:22, Mathias Nyman wrote:
> 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
> .
> 
Thanks very much.
Longfang Liu