linux-kernel - Re: [PATCH] usb:typec:tcpm:support double Rp to Vbus cable as sink

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Message-ID: <56e26444-f289-d017-6225-24658e81ab84@allwinnertech.com>
Date:   Wed, 20 Sep 2023 18:45:47 +0800
From:   Michael Wu <michael@...winnertech.com>
To:     Guenter Roeck <linux@...ck-us.net>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb:typec:tcpm:support double Rp to Vbus cable as sink

On 2023/9/18 22:22, Guenter Roeck wrote:
> On 9/18/23 03:31, Heikki Krogerus wrote:
>> On Thu, Sep 14, 2023 at 08:31:54AM +0800, Michael Wu wrote:
>>> The USB Type-C Cable and Connector Specification defines the wire
>>> connections for the USB Type-C to USB 2.0 Standard-A cable assembly
>>> (Release 2.2, Chapter 3.5.2).
>>> The Notes says that Pin A5 (CC) of the USB Type-C plug shall be 
>>> connected
>>> to Vbus through a resister Rp.
>>> However, there is a large amount of such double Rp connected to Vbus
>>> non-standard cables which produced by UGREEN circulating on the 
>>> market, and
>>> it can affects the normal operations of the state machine easily,
>>> especially to CC1 and CC2 be pulled up at the same time.
>>> In fact, we can regard those cables as sink to avoid abnormal state.
>>>
>>> Message as follow:
>>> [   58.900212] VBUS on
>>> [   59.265433] CC1: 0 -> 3, CC2: 0 -> 3 [state TOGGLING, polarity 0, 
>>> connected]
>>> [   62.623308] CC1: 3 -> 0, CC2: 3 -> 0 [state TOGGLING, polarity 0, 
>>> disconnected]
>>> [   62.625006] VBUS off
>>> [   62.625012] VBUS VSAFE0V
>>>
>>> Signed-off-by: Michael Wu <michael@...winnertech.com>
>>> ---
>>>   drivers/usb/typec/tcpm/tcpm.c | 3 ++-
>>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/usb/typec/tcpm/tcpm.c 
>>> b/drivers/usb/typec/tcpm/tcpm.c
>>> index d962f67c95ae6..beb7143128667 100644
>>> --- a/drivers/usb/typec/tcpm/tcpm.c
>>> +++ b/drivers/usb/typec/tcpm/tcpm.c
>>> @@ -519,7 +519,8 @@ static const char * const pd_rev[] = {
>>>   #define tcpm_port_is_sink(port) \
>>>       ((tcpm_cc_is_sink((port)->cc1) && 
>>> !tcpm_cc_is_sink((port)->cc2)) || \
>>> -     (tcpm_cc_is_sink((port)->cc2) && !tcpm_cc_is_sink((port)->cc1)))
>>> +     (tcpm_cc_is_sink((port)->cc2) && !tcpm_cc_is_sink((port)->cc1)) 
>>> || \
>>> +     (tcpm_cc_is_sink((port)->cc1) && tcpm_cc_is_sink((port)->cc2)))
>>>   #define tcpm_cc_is_source(cc) ((cc) == TYPEC_CC_RD)
>>>   #define tcpm_cc_is_audio(cc) ((cc) == TYPEC_CC_RA)
>>
>> This look OK to me, but I would still like to wait for comments from
>> Guenter - just in case.
>>
> 
> Look at the conditions. Reordered, we end up with
>      (tcpm_cc_is_sink((port)->cc1) && !tcpm_cc_is_sink((port)->cc2)) ||
>      (tcpm_cc_is_sink((port)->cc1) && tcpm_cc_is_sink((port)->cc2))
> which simplifies to
>      tcpm_cc_is_sink((port)->cc1)
> making the complete expression
>      tcpm_cc_is_sink((port)->cc1) ||
>      (tcpm_cc_is_sink((port)->cc2) && !tcpm_cc_is_sink((port)->cc1))
> which simplifies further to
>      tcpm_cc_is_sink((port)->cc1) || tcpm_cc_is_sink((port)->cc2)
> 
> The simplified expression doesn't conflict with other detections, so I am
> ok with it. It might be worthwhile adding a comment to the code, though,
> explaining the reason
> Guenter
> 
>> thanks,
>>
Dear Guenter,

I have modified it according to your opinion, and resend it as patch 
v2[1]. Please review.

[1] 
https://lore.kernel.org/all/20230920063030.66312-1-michael@allwinnertech.com/

-- 
Regards,
Michael Wu