linux-kernel - Re: [PATCH v5 4/4] usb: typec: ucsi: Always set number of alternate modes

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Date: Mon, 24 Jun 2024 16:52:53 +0100
From: Jon Hunter <jonathanh@...dia.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Jameson Thies <jthies@...gle.com>, heikki.krogerus@...ux.intel.com,
 linux-usb@...r.kernel.org, pmalani@...omium.org, bleung@...gle.com,
 abhishekpandit@...omium.org, andersson@...nel.org,
 fabrice.gasnier@...s.st.com, gregkh@...uxfoundation.org,
 hdegoede@...hat.com, neil.armstrong@...aro.org, rajaram.regupathy@...el.com,
 saranya.gopal@...el.com, linux-kernel@...r.kernel.org,
 Benson Leung <bleung@...omium.org>,
 "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v5 4/4] usb: typec: ucsi: Always set number of alternate
 modes


On 24/06/2024 15:33, Dmitry Baryshkov wrote:
> On Mon, 24 Jun 2024 at 16:42, Jon Hunter <jonathanh@...dia.com> wrote:
>>
>>
>> On 24/06/2024 13:51, Jon Hunter wrote:
>>> Hi Jameson,
>>>
>>> On 10/05/2024 21:12, Jameson Thies wrote:
>>>> Providing the number of known alternate modes allows user space to
>>>> determine when device registration has completed. Always register a
>>>> number of known alternate modes for the partner and cable plug, even
>>>> when the number of supported alternate modes is 0.
>>>>
>>>> Reviewed-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
>>>> Reviewed-by: Benson Leung <bleung@...omium.org>
>>>> Signed-off-by: Jameson Thies <jthies@...gle.com>
>>>> ---
>>>> Changes in V5:
>>>> - None.
>>>>
>>>> Changes in V4:
>>>> - None.
>>>>
>>>> Changes in V3:
>>>> - None.
>>>>
>>>> Changes in V2:
>>>> - None.
>>>>
>>>>    drivers/usb/typec/ucsi/ucsi.c | 14 +++++++++++---
>>>>    1 file changed, 11 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/drivers/usb/typec/ucsi/ucsi.c
>>>> b/drivers/usb/typec/ucsi/ucsi.c
>>>> index bb6e57064513d..52a14bfe4107e 100644
>>>> --- a/drivers/usb/typec/ucsi/ucsi.c
>>>> +++ b/drivers/usb/typec/ucsi/ucsi.c
>>>> @@ -812,10 +812,11 @@ static int ucsi_check_altmodes(struct
>>>> ucsi_connector *con)
>>>>        /* Ignoring the errors in this case. */
>>>>        if (con->partner_altmode[0]) {
>>>>            num_partner_am = ucsi_get_num_altmode(con->partner_altmode);
>>>> -        if (num_partner_am > 0)
>>>> -            typec_partner_set_num_altmodes(con->partner,
>>>> num_partner_am);
>>>> +        typec_partner_set_num_altmodes(con->partner, num_partner_am);
>>>>            ucsi_altmode_update_active(con);
>>>>            return 0;
>>>> +    } else {
>>>> +        typec_partner_set_num_altmodes(con->partner, 0);
>>>>        }
>>>>        return ret;
>>>> @@ -1138,7 +1139,7 @@ static int ucsi_check_connection(struct
>>>> ucsi_connector *con)
>>>>    static int ucsi_check_cable(struct ucsi_connector *con)
>>>>    {
>>>>        u64 command;
>>>> -    int ret;
>>>> +    int ret, num_plug_am;
>>>>        if (con->cable)
>>>>            return 0;
>>>> @@ -1172,6 +1173,13 @@ static int ucsi_check_cable(struct
>>>> ucsi_connector *con)
>>>>                return ret;
>>>>        }
>>>> +    if (con->plug_altmode[0]) {
>>>> +        num_plug_am = ucsi_get_num_altmode(con->plug_altmode);
>>>> +        typec_plug_set_num_altmodes(con->plug, num_plug_am);
>>>> +    } else {
>>>> +        typec_plug_set_num_altmodes(con->plug, 0);
>>>> +    }
>>>> +
>>>>        return 0;
>>>>    }

Looking at this some more, the plug is only registered in
ucsi_check_cable() if UCSI_CAP_ALT_MODE_DETAILS is specified
for the Type C controller. The Cypress CCG explicitly clears
this flag.

The following will only call typec_plug_set_num_altmodes()
if the call to ucsi_register_plug() is successful ...

diff --git a/drivers/usb/typec/ucsi/ucsi.c b/drivers/usb/typec/ucsi/ucsi.c
index 134ef4e17d85..e268af88a7d2 100644
--- a/drivers/usb/typec/ucsi/ucsi.c
+++ b/drivers/usb/typec/ucsi/ucsi.c
@@ -1176,13 +1176,13 @@ static int ucsi_check_cable(struct ucsi_connector *con)
                 ret = ucsi_register_altmodes(con, UCSI_RECIPIENT_SOP_P);
                 if (ret < 0)
                         return ret;
-       }
  
-       if (con->plug_altmode[0]) {
-               num_plug_am = ucsi_get_num_altmode(con->plug_altmode);
-               typec_plug_set_num_altmodes(con->plug, num_plug_am);
-       } else {
-               typec_plug_set_num_altmodes(con->plug, 0);
+               if (con->plug_altmode[0]) {
+                       num_plug_am = ucsi_get_num_altmode(con->plug_altmode);
+                       typec_plug_set_num_altmodes(con->plug, num_plug_am);
+               } else {
+                       typec_plug_set_num_altmodes(con->plug, 0);
+               }
         }
  
         return 0;

>> It is crashing because 'con->plug' is not initialised when
>> typec_plug_set_num_altmodes() is called. Do we need to add a check to
>> see if 'con->plug' is valid in ucsi_check_cable()?
> 
> Yes. Either of  con->calbe and con->plug can be NULL.

Thanks for confirming.

Jon

-- 
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