From: Roger Quadros <rogerq@ti.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: <balbi@kernel.org>, <Dylan.Howey@tennantco.com>,
<linux-usb@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
"# v4 . 13+" <stable@vger.kernel.org>
Subject: Re: [PATCH v2][RESEND] usb: gadget: core: Fix ->udc_set_speed() speed handling
Date: Thu, 2 Nov 2017 10:53:08 +0200 [thread overview]
Message-ID: <46a6dae0-b9f1-9d7b-d6c7-8f3c8f59ca6e@ti.com> (raw)
In-Reply-To: <Pine.LNX.4.44L0.1711011133220.1770-100000@iolanthe.rowland.org>
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
Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
next prev parent reply other threads:[~2017-11-02 8:53 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-31 13:01 [PATCH] usb: dwc3: gadget: Fix .udc_set_speed() Roger Quadros
2017-10-31 13:24 ` Felipe Balbi
2017-10-31 13:27 ` Roger Quadros
2017-10-31 13:47 ` [PATCH v2] " Roger Quadros
2017-10-31 13:54 ` Roger Quadros
2017-10-31 13:56 ` [PATCH v2][RESEND] usb: gadget: core: Fix ->udc_set_speed() speed handling Roger Quadros
2017-11-01 14:24 ` Alan Stern
2017-11-01 15:11 ` Roger Quadros
2017-11-01 15:45 ` Alan Stern
2017-11-02 8:53 ` Roger Quadros [this message]
2017-11-02 14:14 ` Alan Stern
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