linux-kernel - Re: [PATCH] usb: dwc2: gadget: initialize max

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Message-ID: <35819bf8-7653-da00-fb56-8ffd56fa3944@synopsys.com>
Date:   Mon, 6 Dec 2021 05:21:29 +0000
From:   Minas Harutyunyan <Minas.Harutyunyan@...opsys.com>
To:     John Keeping <john@...anate.com>,
        Minas Harutyunyan <Minas.Harutyunyan@...opsys.com>
CC:     "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Argishti Aleksanyan <argishti.aleksanyan@...opsys.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: dwc2: gadget: initialize max_speed from params

On 12/3/2021 3:36 PM, John Keeping wrote:
> Hi Minas,
> 
> On Fri, Dec 03, 2021 at 05:49:36AM +0000, Minas Harutyunyan wrote:
>> On 12/2/2021 9:17 PM, John Keeping wrote:
>>> DWC2 may be paired with a full-speed PHY which is not capable of
>>> high-speed operation.  Report this correctly to the gadget core by
>>> setting max_speed from the core parameters.
>>>
>>> Prior to commit 5324bad66f09f ("usb: dwc2: gadget: implement
>>> udc_set_speed()") this didn't cause the hardware to be configured
>>> incorrectly, although the speed may have been reported incorrectly.  But
>>> after that commit params.speed is updated based on a value passed in by
>>> the gadget core which may set it to a faster speed than is supported by
>>> the hardware.  Initialising the max_speed parameter ensures the speed
>>> passed to dwc2_gadget_set_speed() will be one supported by the hardware.
>>>
>>> Fixes: 5324bad66f09f ("usb: dwc2: gadget: implement udc_set_speed()")
>>> Signed-off-by: John Keeping <john@...anate.com>

Acked-by: Minas Harutyunyan <Minas.Harutyunyan@...opsys.com>

>>> ---
>>>    drivers/usb/dwc2/gadget.c | 13 ++++++++++++-
>>>    1 file changed, 12 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/usb/dwc2/gadget.c b/drivers/usb/dwc2/gadget.c
>>> index b884a83b26a6e..2bc03f41c70ad 100644
>>> --- a/drivers/usb/dwc2/gadget.c
>>> +++ b/drivers/usb/dwc2/gadget.c
>>> @@ -4974,7 +4974,18 @@ int dwc2_gadget_init(struct dwc2_hsotg *hsotg)
>>>    		hsotg->params.g_np_tx_fifo_size);
>>>    	dev_dbg(dev, "RXFIFO size: %d\n", hsotg->params.g_rx_fifo_size);
>>>    
>>> -	hsotg->gadget.max_speed = USB_SPEED_HIGH;
>>> +	switch (hsotg->params.speed) {
>>> +	case DWC2_SPEED_PARAM_LOW:
>>> +		hsotg->gadget.max_speed = USB_SPEED_LOW;
>>> +		break;
>>> +	case DWC2_SPEED_PARAM_FULL:
>>> +		hsotg->gadget.max_speed = USB_SPEED_FULL;
>>> +		break;
>>> +	default:
>>> +		hsotg->gadget.max_speed = USB_SPEED_HIGH;
>>> +		break;
>>> +	}
>>> +
>>>    	hsotg->gadget.ops = &dwc2_hsotg_gadget_ops;
>>>    	hsotg->gadget.name = dev_name(dev);
>>>    	hsotg->gadget.otg_caps = &hsotg->params.otg_caps;
>>>
>>
>> Just setting gadget's max_speed doesn't resolve described issue. After
>> setting gadget's max_speed in your patch, it doesn't used in driver at
>> all. Per me, you need also fix dwc2_gadget_set_speed() function by
>> checking requested speed with max_speed: if requested speed higher than
>> max_speed then set speed to max_speed.
> 
> Setting the max_speed here restricts what the gadget core will pass in
> to the .udc_set_speed hook, see usb_gadget_udc_set_speed():
> 
> 	s = min(speed, udc->gadget->max_speed);
> 	udc->gadget->ops->udc_set_speed(udc->gadget, s);
> 
> We can't add a check in dwc2_gadget_set_speed() because the original
> capability may have been lost, for example if a high-speed capable
> device is configured for full-speed operation then hsotg->params.speed
> is set to full-speed and there's nothing that says the device is capable
> of high-speed when setting the speed back again.
> 
> I believe this patch is sufficient because of the guarantees by the
> gadget core that we will never be called with a speed that is faster
> than we support.
> 
> 
> Regards,
> John
>