lkml.org 
[lkml]   [2019]   [Aug]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v10 5/6] usb:cdns3 Add Cadence USB3 DRD Driver
From
Date


On 13/08/2019 10:30, Chunfeng Yun wrote:
> On Mon, 2019-08-12 at 16:04 +0300, Roger Quadros wrote:
>>
>> On 12/08/2019 15:46, Felipe Balbi wrote:
>>>
>>> Hi,
>>>
>>> Roger Quadros <rogerq@ti.com> writes:
>>>>> The sysfs file we expose from the class for the role switches is
>>>>> primarily meant for supporting proprietary protocols that require us
>>>>> to basically override the connector USB data role. The default role
>>>>> should always be selected in the drivers.
>>>>
>>>> OK. Let's take this example
>>>> - Port is dual-role port micro AB.
>>>> - microAB to type-A adapter is connected which pulls ID low. port transitions
>>>> to "host" role by the controller driver.
>>>> - proprietary protocol want to switch role to device role so writes "device" to
>>>> mode switch sysfs. port transitions to "device" role.
>>>>
>>>> Now, how does controller driver know to fall back to HW based role switching?
>>>
>>> Use a 'disconnect' or 'suspend' event to go reset it? But that should,
>>> probably, be done at kernel space, no?
>>>
>>
>> Yes that could be one option.
>> So after a disconnect, sysfs role should reflect actual hardware role. correct?
>
> Maybe it's difficult to support both HW based role switch and SW based
> role switch by sysfs at the same if the HW's FSM rely on, such as, the
> state of Vbus pin or ID pin. Likes the upper example, when user writes
> "device" to mode switch sysfs, the driver should skip the HW state of ID
> pin, due to it's state is Low, or force it as High.
>

We do need a clear way of indicating that SW wants to override so HW
state is ignored.

> Another option way is that introduces a property in DTS to indicate the
> way the driver want to use (HW based or SW based, usb_role_switch
> doesn't provide this information for the controller driver), but is not
> flexible enough.

That is not good enough for us. We need both HW and SW based role switching.

Can we introduce a new state (e.g. "auto") in usb_role_switch. This would
explicitly indicate the driver to do HW based switching.

This way we don't need to depend on connect/disconnect events and can
do role switch tests even without cable/device connected.

--
cheers,
-roger
Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki

\
 
 \ /
  Last update: 2019-08-13 09:49    [W:0.065 / U:19.364 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site