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From: Mats Karrman <>
To: Heikki Krogerus <>
Subject: [RFC,1/7] usb: typec: Generalize mux mode names
Date: Fri, 11 May 2018 21:28:04 +0200	[thread overview]
Message-ID: <> (raw)

On 2018-05-11 13:14, Heikki Krogerus wrote:

> On Fri, May 11, 2018 at 11:05:55AM +0200, Mats Karrman wrote:
>> On 2018-05-10 19:49, Heikki Krogerus wrote:
>>> On Thu, May 10, 2018 at 10:04:21AM +0200, Mats Karrman wrote:
>>>> Hi,
>>>> On 05/09/2018 02:49 PM, Heikki Krogerus wrote:
>>>>> On Tue, May 08, 2018 at 09:10:13PM +0200, Mats Karrman wrote:
>>>>>> Hi,
>>>>>> On 05/08/2018 04:25 PM, Heikki Krogerus wrote:
>>>>>>> Hi,
>>>>>>> On Mon, May 07, 2018 at 11:19:40PM +0200, Mats Karrman wrote:
>>>>>>>>>> Even so, when the mux driver "set" function is called, it will just get the
>>>>>>>>>> mode argument but since the mode (TYPEC_STATE_...) is overlapping for different
>>>>>>>>>> AMs if I understand your proposal correctly, the mux also needs to know what AM
>>>>>>>>>> is active.
>>>>>>>>>> Does this imply that the mux set function signature need to change?
>>>>>>>>> My plan was actually to propose we get rid of the current mux handling
>>>>>>>>> (just leave the orientation switch) in favour of the notifications I'm
>>>>>>>>> introducing with the type-c bus for the alternate modes. The current
>>>>>>>>> mux handling is definitely not enough, and does not work in every
>>>>>>>>> scenario, like also you pointed out.
>>>>>>>> So, the mux need to subscribe to each svid:mode pair it is interested in using
>>>>>>>> typec_altmode_register_notifier() and then use those callbacks to switch the correct
>>>>>>>> signals to the connector. And a driver for an off-the-shelf mux device could have
>>>>>>>> the translation between svid:mode pairs and mux device specific control specified by
>>>>>>>> of/acpi properties. Right?
>>>>>>> Yes. That is the plan. Would it work for you?
>>>>>> I think so. I'll give it a go. When about do you think you'll post the next version
>>>>>> of your RFC? Or do you have an updated series available somewhere public?
>>>>> I'll try to put together and post the next version tomorrow.
>>>>> My original plan was actually to use just the notifications with the
>>>>> muxes, but one thing to consider with the notifications is that in
>>>>> practice we have to increment the ref count for the alt mode devices
>>>>> when ever something registers a notifier.
>>>>> To me that does not feel ideal. The dependency should go the other way
>>>>> around in case of the muxes. That is why I liked the separate API and
>>>>> handling for the muxes felt better, as it will do just that. The mux
>>>>> is then a "service" that the port driver can as for, and if it gets a
>>>>> handle to a mux, the mux will have its ref count incremented.
>>>>> So I think fixing the mux API would perhaps be better after all.
>>>>> Thoughts?
>>>> So, we're back to a mux API similar to the current one, where:
>>>> - the port driver and the mux driver are connected through "graph"
>>>> - alt mode driver finds its port mux using the typec class mux api
>>>> - the mux mode setting function arguments now include both svid and mode
>>>> I like that.
>>>> One thought that popped up again is if we, somewhere down the line,
>>>> will see some super device that support many different alternate modes
>>>> on the same port and therefore will need to have multiple mux devices?
>>>> However I think the mux api could be extended (later on) to support some
>>>> aggregate mux device that manages multiple physical devices.
>>> If we simply had always a mux for every alternate mode, that would not
>>> be a problem. So the port would have its own mux, and every supported
>>> alternate mode also had its own. I think that removes the need to deal
>>> with the svid:mode when using the muxes, as they are already tied to a
>>> specific alternate modes, right? With a single mux device, for example
>>> pi3usb30532, the driver just needs to register a mux for the port and
>>> separate mux for DP, but I don't think that's a huge problem.
>> Hmm... As an hypothetical example I have written a driver for another mux
>> from TI and according to its data sheet:
>> """
>> The HD3SS460 is a generic analog differential
>> passive switch that can work for any high speed
>> interface applications as long as it is biased at a
>> common mode voltage range of 0-2V and has
>> differential signaling with differential amplitude up to
>> 1800mVpp....
>> """
>> What I am thinking is that it e.g. would be possible to use this/a mux with USBSS +
>> 2ch DP + 2ch something else (HDMI?, ThunderBolt?, ???). The problem here is
>> that it is a general mux device so the driver writer does not know what types of
>> muxes to register. I guess it could also be configured using properties but that
>> would be very complicated.
> Why? All the mux driver needs to get from device properties is the
> SVID and the mode.

Sigh... Again, if the same mux handles signals for more than one alternate mode
the driver won't know what alternate mode is intended if it only receives the
connector state which use overlapping numbers for different alternate modes.

> Is there a problem providing both svid and sub-mode in the mux set call? The
>> partner drivers should all know what svid they implement.
> By sub-mode, what do you mean? The SVID specific connector state value
> you already get with the mux ->set callback. The mode index number is
> not very useful (with DP for example it will always be 1).
> In any case, the mux driver will still need to interpret the SVID
> specific connector states, so what would it change if we supplied also
> the SVID and mode on top of that with the ->set callback?


> Thanks,
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             reply	other threads:[~2018-05-11 19:28 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-11 19:28 Mats Karrman [this message]
  -- strict thread matches above, loose matches on Subject: below --
2018-05-21 13:04 [RFC,1/7] usb: typec: Generalize mux mode names Heikki Krogerus
2018-05-18  5:26 Mats Karrman
2018-05-17 11:50 Heikki Krogerus
2018-05-16 21:11 Mats Karrman
2018-05-16 11:43 Heikki Krogerus
2018-05-15 21:24 Mats Karrman
2018-05-15  7:30 Heikki Krogerus
2018-05-09 12:49 Heikki Krogerus
2018-05-08 19:10 Mats Karrman
2018-05-08 14:25 Heikki Krogerus
2018-05-07 21:19 Mats Karrman
2018-05-07 13:39 Heikki Krogerus
2018-05-04 16:57 Mats Karrman
2018-05-04 14:56 Heikki Krogerus
2018-05-02 13:13 Mats Karrman
2018-05-02  8:25 Heikki Krogerus
2018-05-02  8:23 Heikki Krogerus
2018-05-01 22:21 Mats Karrman

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