Re: [PATCH v6 03/13] media: v4l2-fwnode: add initial connector parsing support

[Marco Felsch <m.felsch@pengutronix.de>]

Hi Laurent,

On 19-08-15 15:48, Laurent Pinchart wrote:
> Hi Marco,
> 
> On Fri, Aug 09, 2019 at 02:16:06PM +0200, Marco Felsch wrote:
> > On 19-05-16 19:51, Laurent Pinchart wrote:
> > > On Tue, May 14, 2019 at 03:20:04PM -0300, Mauro Carvalho Chehab wrote:
> > >> Em Mon, 6 May 2019 12:10:41 +0200 Hans Verkuil escreveu:
> > >>> On 4/15/19 2:44 PM, Marco Felsch wrote:
> > >>>> The patch adds the initial connector parsing code, so we can move from a
> > >>>> driver specific parsing code to a generic one. Currently only the
> > >>>> generic fields and the analog-connector specific fields are parsed. Parsing
> > >>>> the other connector specific fields can be added by a simple callbacks.
> > >>>> 
> > >>>> Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
> > >>>> Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
> > >>>> ---
> > >>>> [1] https://patchwork.kernel.org/cover/10794703/
> > >>>> 
> > >>>> v6:
> > >>>> - use 'unsigned int' count var
> > >>>> - fix comment and style issues
> > >>>> - place '/* fall through */' to correct places
> > >>>> - fix error handling and cleanup by releasing fwnode
> > >>>> - drop vga and dvi parsing support as those connectors are rarely used
> > >>>>   these days
> > >>>> 
> > >>>> v5:
> > >>>> - s/strlcpy/strscpy/
> > >>>> 
> > >>>> v2-v4:
> > >>>> - nothing since the patch was squashed from series [1] into this
> > >>>>   series.
> > >>>> 
> > >>>>  drivers/media/v4l2-core/v4l2-fwnode.c | 111 ++++++++++++++++++++++++++
> > >>>>  include/media/v4l2-fwnode.h           |  16 ++++
> > >>>>  2 files changed, 127 insertions(+)
> > >>>> 
> > >>>> diff --git a/drivers/media/v4l2-core/v4l2-fwnode.c b/drivers/media/v4l2-core/v4l2-fwnode.c
> > >>>> index 20571846e636..f1cca95c8fef 100644
> > >>>> --- a/drivers/media/v4l2-core/v4l2-fwnode.c
> > >>>> +++ b/drivers/media/v4l2-core/v4l2-fwnode.c
> > >>>> @@ -592,6 +592,117 @@ void v4l2_fwnode_put_link(struct v4l2_fwnode_link *link)
> > >>>>  }
> > >>>>  EXPORT_SYMBOL_GPL(v4l2_fwnode_put_link);
> > >>>>  
> > >>>> +static const struct v4l2_fwnode_connector_conv {
> > >>>> +	enum v4l2_connector_type type;
> > >>>> +	const char *name;
> > > 
> > > Maybe compatible instead of name ?
> > 
> > Okay, I can change that.
> > 
> > >>>> +} connectors[] = {
> > >>>> +	{
> > >>>> +		.type = V4L2_CON_COMPOSITE,
> > >>>> +		.name = "composite-video-connector",
> > >>>> +	}, {
> > >>>> +		.type = V4L2_CON_SVIDEO,
> > >>>> +		.name = "svideo-connector",
> > >>>> +	}, {
> > >>>> +		.type = V4L2_CON_HDMI,
> > >>>> +		.name = "hdmi-connector",
> > >>>> +	},
> > >>>> +};
> > >>>> +
> > >>>> +static enum v4l2_connector_type
> > >>>> +v4l2_fwnode_string_to_connector_type(const char *con_str)
> > >>>> +{
> > >>>> +	unsigned int i;
> > >>>> +
> > >>>> +	for (i = 0; i < ARRAY_SIZE(connectors); i++)
> > >>>> +		if (!strcmp(con_str, connectors[i].name))
> > >>>> +			return connectors[i].type;
> > >>>> +
> > >>>> +	/* no valid connector found */
> > > 
> > > The usual comment style in this file is to start with a capital letter
> > > and end sentences with a period. I would however drop this comment, it's
> > > not very useful. The other comments should be updated accordingly.
> > 
> > I will change my comments and drop this one.
> > 
> > >>>> +	return V4L2_CON_UNKNOWN;
> > >>>> +}
> > >>>> +
> > >>>> +static int
> > >>>> +v4l2_fwnode_connector_parse_analog(struct fwnode_handle *fwnode,
> > >>>> +				   struct v4l2_fwnode_connector *vc)
> > >>>> +{
> > >>>> +	u32 tvnorms;
> > >>>> +	int ret;
> > >>>> +
> > >>>> +	ret = fwnode_property_read_u32(fwnode, "tvnorms", &tvnorms);
> > >>>> +
> > >>>> +	/* tvnorms is optional */
> > >>>> +	vc->connector.analog.supported_tvnorms = ret ? V4L2_STD_ALL : tvnorms;
> > >>>> +
> > >>>> +	return 0;
> > >>>> +}
> > >>>> +
> > > 
> > > Please document all exported functions with kerneldoc.
> > 
> > It is documented within the header file. To be aligned with the other
> > functions I wouldn't change that.
> 
> It's not your fault, but this policy REALLY makes review painful and is
> EXTREMELY annoying.

I'm with you..

> > >>>> +int v4l2_fwnode_parse_connector(struct fwnode_handle *__fwnode,
> > >>>> +				struct v4l2_fwnode_connector *connector)
> > >>>> +{
> > >>>> +	struct fwnode_handle *fwnode;
> > >>>> +	struct fwnode_endpoint __ep;
> > >>>> +	const char *c_type_str, *label;
> > >>>> +	int ret;
> > >>>> +
> > >>>> +	memset(connector, 0, sizeof(*connector));
> > >>>> +
> > >>>> +	fwnode = fwnode_graph_get_remote_port_parent(__fwnode);
> > > 
> > > I would rename the argument __fwnode to fwnode, and rename the fwnode
> > > variable to remote (or similar) to make this clearer.
> > 
> > Okay.
> > 
> > >>>> +	if (!fwnode)
> > >>>> +		return -EINVAL;
> > > 
> > > Is EINVAL the right error here ? Wouldn't it be useful for the caller to
> > > differentiate between unconnected connector nodes and invalid ones ?
> > 
> > Yes it would. Should I return ENOLINK instead?
> 
> Good idea.

Good because I used it in my v7 :-)

> > >>>> +
> > >>>> +	/* parse all common properties first */
> > >>>> +	/* connector-type is stored within the compatible string */
> > >>>> +	ret = fwnode_property_read_string(fwnode, "compatible", &c_type_str);
> > > 
> > > Prefixing or postfixing names with types is usually frowned upon. You
> > > could rename this to type_name for instance.
> > 
> > Okay.
> > 
> > >>>> +	if (ret) {
> > >>>> +		fwnode_handle_put(fwnode);
> > >>>> +		return -EINVAL;
> > >>>> +	}
> > >>>> +
> > >>>> +	connector->type = v4l2_fwnode_string_to_connector_type(c_type_str);
> > >>>> +
> > >>>> +	fwnode_graph_parse_endpoint(__fwnode, &__ep);
> > >>>> +	connector->remote_port = __ep.port;
> > >>>> +	connector->remote_id = __ep.id;
> > >>>> +
> > >>>> +	ret = fwnode_property_read_string(fwnode, "label", &label);
> > >>>> +	if (!ret) {
> > >>>> +		/* ensure label doesn't exceed V4L2_CONNECTOR_MAX_LABEL size */
> > >>>> +		strscpy(connector->label, label, V4L2_CONNECTOR_MAX_LABEL);
> > >>>> +	} else {
> > >>>> +		/*
> > >>>> +		 * labels are optional, if none is given create one:
> > >>>> +		 * <connector-type-string>@port<endpoint_port>/ep<endpoint_id>
> > >>>> +		 */
> > >>>> +		snprintf(connector->label, V4L2_CONNECTOR_MAX_LABEL,
> > >>>> +			 "%s@port%u/ep%u", c_type_str, connector->remote_port,
> > >>>> +			 connector->remote_id);
> > > 
> > > Should we really try to create labels when none is available ? If so
> > > this needs much more careful thoughts, we need to think about what the
> > > label will be used for, and create a good naming scheme accordingly. If
> > > the label will be displayed to the end-user I don't think the above name
> > > would be very useful, it would be best to leave it empty and let
> > > applications create a name based on the connector type and other
> > > information they have at their disposal.
> > 
> > Hm.. I don't have a strong opinion on that. If the others are with you I
> > will leave it empty.
> > 
> > >>>> +	}
> > >>>> +
> > >>>> +	/* now parse the connector specific properties */
> > >>>> +	switch (connector->type) {
> > >>>> +	case V4L2_CON_COMPOSITE:
> > >>>> +		/* fall through */
> > > 
> > > I don't think you need a fall-through comment when the two cases are
> > > adjacent with no line in-between.
> > 
> > Hm.. I don't know the compiler behaviour. According the official
> > gcc documentation [1] I would not leave that.
> 
> Not leave the fall-through comment, and thus remove it ? :-) I really
> think it's not needed (otherwise imagine how the big switch-case in
> v4l2-ctrls.c would look like for instance).

Yes you're right. I dopped that in my v7.

> 
> > [1] https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html
> > 
> > >>>> +	case V4L2_CON_SVIDEO:
> > >>>> +		ret = v4l2_fwnode_connector_parse_analog(fwnode, connector);
> > >>>> +		break;
> > >>>> +	case V4L2_CON_HDMI:
> > >>>> +		pr_warn("Connector specific parsing is currently not supported for %s\n",
> > >>>> +			c_type_str);  
> > >>> 
> > >>> Why warn? Just drop this.
> > >> 
> > >> good point. I would prefer to have some warning here, in order to warn a
> > >> developer that might be using it that this part of the code would require 
> > >> some change.
> > >> 
> > >> perhaps pr_warn_once()?
> > >>
> > >>>> +		ret = 0;
> > >>>> +		break;
> > > 
> > > If it's not supported we should warn and return an error. Otherwise we
> > > should be silent and return success. Combining a warning with success
> > > isn't a good idea, this is either a normal case or an error, not both.
> > 
> > The generic part still applies and is valid. That was the reason why I
> > did return success.
> 
> But the HDMI-specific part won't work, so the code will likely not
> operate correctly. I'd rather make it an error to for developers using
> HDMI connectors to fix it.

Hm.. Since you and Hans have your concerns about it I can change that
behaviour.

Regards,
  Marco

> > >>>> +	case V4L2_CON_UNKNOWN:
> > >>>> +		/* fall through */
> > >>>> +	default:
> > >>>> +		pr_err("Unknown connector type\n");
> > >>>> +		ret = -EINVAL;
> > >>>> +	};
> > >>>> +
> > >>>> +	fwnode_handle_put(fwnode);
> > >>>> +
> > >>>> +	return ret;
> > >>>> +}
> > >>>> +EXPORT_SYMBOL_GPL(v4l2_fwnode_parse_connector);
> > >>>> +
> > >>>>  static int
> > >>>>  v4l2_async_notifier_fwnode_parse_endpoint(struct device *dev,
> > >>>>  					  struct v4l2_async_notifier *notifier,
> > >>>> diff --git a/include/media/v4l2-fwnode.h b/include/media/v4l2-fwnode.h
> > >>>> index f4df1b95c5ef..e072f2915ddb 100644
> > >>>> --- a/include/media/v4l2-fwnode.h
> > >>>> +++ b/include/media/v4l2-fwnode.h
> > >>>> @@ -269,6 +269,22 @@ int v4l2_fwnode_parse_link(struct fwnode_handle *fwnode,
> > >>>>   */
> > >>>>  void v4l2_fwnode_put_link(struct v4l2_fwnode_link *link);
> > >>>>  
> > > 
> > > And I see here that the function is documented. One more reason to move
> > > kerneldoc to the .c files...
> > 
> > Please check my comment above.
> 
> I know, it's not your fault, I was complaining about the state of the
> universe in general :-)
> 
> > >>>> +/**
> > >>>> + * v4l2_fwnode_parse_connector() - parse the connector on endpoint
> > >>>> + * @fwnode: pointer to the endpoint's fwnode handle where the connector is
> > >>>> + *          connected to
> > > 
> > > This is very unclear, I would interpret that as the remote endpoint, not
> > > the local endpoint. Could you please try to clarify the documentation ?
> > 
> > Hm.. I have no good idea how I should describe it..
> > 
> > """
> > The device (local) endpoint fwnode handle on which the connector is
> > connected to using the remote-enpoint property.
> > """
> > 
> > >>>> + * @connector: pointer to the V4L2 fwnode connector data structure
> > >>>> + *
> > >>>> + * Fill the connector data structure with the connector type, label and the
> > >>>> + * endpoint id and port where the connector belongs to. If no label is present
> > >>>> + * a unique one will be created. Labels with more than 40 characters are cut.
> > >>>> + *
> > >>>> + * Return: %0 on success or a negative error code on failure:
> > >>>> + *	   %-EINVAL on parsing failure
> > >>>> + */
> > >>>> +int v4l2_fwnode_parse_connector(struct fwnode_handle *fwnode,
> > >>>> +				struct v4l2_fwnode_connector *connector);
> > >>>> +
> > >>>>  /**
> > >>>>   * typedef parse_endpoint_func - Driver's callback function to be called on
> > >>>>   *	each V4L2 fwnode endpoint.
> 
> -- 
> Regards,
> 
> Laurent Pinchart
> 

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