linux-kernel - Re: [PATCH v6 02/17] media: v4l2: async: Allow searching for asd of any type

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Date:   Wed, 26 Sep 2018 10:49:18 -0700
From:   Steve Longerbeam <steve_longerbeam@...tor.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>
CC:     Steve Longerbeam <slongerbeam@...il.com>,
        <linux-media@...r.kernel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Niklas Söderlund 
        <niklas.soderlund+renesas@...natech.se>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Sebastian Reichel <sre@...nel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 02/17] media: v4l2: async: Allow searching for asd of
 any type

Hi Mauro, Sakari,


On 09/26/2018 03:40 AM, Sakari Ailus wrote:
> Hi Mauro, Steve,
>
> On Wed, Sep 26, 2018 at 06:33:35AM -0300, Mauro Carvalho Chehab wrote:
>> Em Tue, 25 Sep 2018 18:05:36 -0700
>> Steve Longerbeam <steve_longerbeam@...tor.com> escreveu:
>>
>>> On 09/25/2018 03:20 PM, Mauro Carvalho Chehab wrote:
>>>> Em Tue, 25 Sep 2018 14:04:21 -0700
>>>> Steve Longerbeam <steve_longerbeam@...tor.com> escreveu:
>>>>   
>>>>>>      
>>>>>>> @@ -392,12 +406,11 @@ static int __v4l2_async_notifier_register(struct v4l2_async_notifier *notifier)
>>>>>>>     		case V4L2_ASYNC_MATCH_CUSTOM:
>>>>>>>     		case V4L2_ASYNC_MATCH_DEVNAME:
>>>>>>>     		case V4L2_ASYNC_MATCH_I2C:
>>>>>>> -			break;
>>>>>>>     		case V4L2_ASYNC_MATCH_FWNODE:
>>>>>>> -			if (v4l2_async_notifier_fwnode_has_async_subdev(
>>>>>>> -				    notifier, asd->match.fwnode, i)) {
>>>>>>> +			if (v4l2_async_notifier_has_async_subdev(
>>>>>>> +				    notifier, asd, i)) {
>>>>>>>     				dev_err(dev,
>>>>>>> -					"fwnode has already been registered or in notifier's subdev list\n");
>>>>>>> +					"asd has already been registered or in notifier's subdev list\n");
>>>>>> Please, never use "asd" on messages printed to the user. While someone
>>>>>> may understand it while reading the source code, for a poor use,
>>>>>> "asd" is just a random sequence of 3 characters.
>>>>> I will change the message to read:
>>>>>
>>>>> "subdev descriptor already listed in this or other notifiers".
>>>> Perfect!
>>> But the error message is removed in the subsequent patch
>>> "[PATCH 03/17] media: v4l2: async: Add v4l2_async_notifier_add_subdev".
>>>
>>> I could bring it back as a dev_dbg() in v4l2_async_notifier_asd_valid(), but
>>> this shouldn't be a dev_err() anymore since it is up to the media platform
>>> to decide whether an already existing subdev descriptor is an error.
>> Hmm... that's an interesting discussion... what cases do you think it
>> would be fine to try to register twice an asd notifier?

It should be a fairly common case that a sub-device has multiple fwnode
output ports. In that case it's possible multiple sub-devices downstream
from it will each encounter it when parsing the fwnode graph, and attempt
to add it to their notifiers asd_list multiple times. That isn't an 
error, any
attempt to add it after the first add should be ignored.

imx-media is an example, there is a CSI-2 transmitter with four fwnode
output ports for each CSI-2 virtual channel. Those channels each go to
one of four Camera Sensor Interface in the imx6 IPU. So each CSI will
encounter the CSI-2 transmitter when parsing its fwnode ports.


> Only the error message is removed; this case is still considered an error.
> I think it'd be better to keep this error message; it helps debugging.

Ok I will add it back, but it should be a dev_dbg().

Steve

>
>> Haven't write myself any piece of code using async framework, on a first
>> glance, trying to register twice sounds like an error to me.
>>
>> Sakari, what do you think?