linux-kernel - Re: [PATCH v2 3/3] usb: typec: tcpm: Get Sink VDO from fwnode

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Date:   Sun, 31 Jan 2021 21:44:41 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Kyle Tso <kyletso@...gle.com>
Cc:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Hans de Goede <hdegoede@...hat.com>, robh+dt@...nel.org,
        Badhri Jagan Sridharan <badhri@...gle.com>,
        USB <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, devicetree@...r.kernel.org
Subject: Re: [PATCH v2 3/3] usb: typec: tcpm: Get Sink VDO from fwnode

On 1/31/21 9:11 PM, Kyle Tso wrote:
> On Mon, Feb 1, 2021 at 12:02 AM Guenter Roeck <linux@...ck-us.net> wrote:
>>
>> On 1/31/21 7:18 AM, Kyle Tso wrote:
>>> Commit a079973f462a ("usb: typec: tcpm: Remove tcpc_config
>>> configuration mechanism") removed the tcpc_config which includes the
>>> Sink VDO and it is not yet added back with fwnode. Add it now.
>>>
>>> Signed-off-by: Kyle Tso <kyletso@...gle.com>
>>> ---
>>> Changes since v1:
>>> - updated the commit message
>>>
>>>  drivers/usb/typec/tcpm/tcpm.c | 12 ++++++++++++
>>>  1 file changed, 12 insertions(+)
>>>
>>> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
>>> index 403a483645dd..84c8a52f8af1 100644
>>> --- a/drivers/usb/typec/tcpm/tcpm.c
>>> +++ b/drivers/usb/typec/tcpm/tcpm.c
>>> @@ -5677,6 +5677,18 @@ static int tcpm_fw_get_caps(struct tcpm_port *port,
>>>                       port->new_source_frs_current = frs_current;
>>>       }
>>>
>>> +     ret = fwnode_property_read_u32_array(fwnode, "sink-vdos", NULL, 0);
>>
>> fwnode_property_count_u32(), maybe ?
>>
> That's the same and looks like fwnode_property_count_u32 is better to read.
> I will revise it in the next version.
> 
>>> +     if (ret <= 0 && ret != -EINVAL) {
>>> +             return -EINVAL;
>>
>> Why return any error except -EINVAL (including return values of 0) as -EINVAL,
>> and -EINVAL as no error ?
>>
> sink-vdos is not a mandatory property which means -EINVAL is acceptable.
> 
> If the return < 0 and the value is not -EINVAL, it means that the
> error is other than "not present" in the device tree.
> If the return == 0, it means that the sink-vdos is present in the
> device tree but no value inside it.

I think that should return -ENODATA. Not sure if/when it would actually return 0.

> Both of the above situations are not acceptable.
> 

Personally I would prefer that a bit more explicit in the code, ie
handle errors first and drop the else statement below. But maybe
that is just me.

>>> +     } else if (ret > 0) {
>>> +             port->nr_snk_vdo = min(ret, VDO_MAX_OBJECTS);
>>> +             ret = fwnode_property_read_u32_array(fwnode, "sink-vdos",
>>> +                                                  port->snk_vdo,
>>> +                                                  port->nr_snk_vdo);
>>> +             if (ret < 0)
>>> +                     return -EINVAL;
>>
>> static analyzer code used to complain about overriding error codes.
>> Not sure if that is still true. Either case, why not return the
>> original error ?
>>
> Returning the original error codes is good. I just followed the return
> value of other error handling in this function.
> will revise it in the next version.
> 
Never mind, with the rest of the code being similar I guess that either
static analyzers gave up complaining or they already have a field day
anyway.

Thanks,
Guenter

> Thanks,
> Kyle
> 
> 
> 
>> Thanks,
>> Guenter
>>
>>> +     }
>>> +
>>>       return 0;
>>>  }
>>>
>>>
>>