On 01/11/17 17:45, Alan Stern wrote:
> On Wed, 1 Nov 2017, Roger Quadros wrote:
>
>>> Roger, would you like to send in a follow-up patch that removes the now
>>> unnecessary code from dummy_udc_set_speed() in dummy_hcd.c?
>>>
>>
>> Sure. I have a question though.
>>
>> In dummy_udc_set_speed() we should just set gadget.speed to whatever is passed in speed.
>> This will be the maximum supported speed by the gadget function driver.
>
> Following your patch, it will be the maximum speed supported by the
> gadget function driver or the maximum speed supported by the UDC
> driver, whichever is lower. That's the whole point of your patch,
> right?
Yes.
>
>> However, is it possible that the gadget will be connected at a lower speed than that?
>
> Yes, it is possible to connect at a speed lower than the function
> driver's maximum speed. The connection speed for dummy-hcd is
> controlled by a pair of module parameters: is_super_speed and
> is_high_speed.
>
>> I see gadget.speed being updated in dummy_hub_control() GetPortStatus: case, but not
>> in case of USB_SPEED_HIGH and USB_SPEED_LOW.
>
> Here's what the code does, in outline form:
>
> switch (dum_hcd->dum->gadget.speed) {
> case USB_SPEED_HIGH:
> ...
> break;
> case USB_SPEED_LOW:
> ...
> break;
> default:
> dum_hcd->dum->gadget.speed = USB_SPEED_FULL;
> break;
> }
>
> In other words, if gadget.speed isn't USB_SPEED_HIGH or USB_SPEED_LOW,
> set it to USB_SPEED_FULL. And this is all under the case where the
> connection is USB-2, not USB-3 or higher.
>
> How is this related to the requested change to dummy_udc_set_speed()?
With or without the requested change to dummy_udc_set_speed() there will
never be a case when gadget.speed isn't already USB_SPEED_FULL
if connection is USB-2 and gadget.speed is not USB_SPEED_HIGH or USB_SPEED_LOW.
So in the above code snippet, default: portion is redundant.
But that can be fixed in a separate patch.
--
cheers,
-roger
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