linux-kernel - Re: [PATCH v3] media: v4l2-ctrl: add a helper function to modify the menu

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Message-Id: <201209131353.34497.hansverk@cisco.com>
Date:	Thu, 13 Sep 2012 13:53:34 +0200
From:	Hans Verkuil <hansverk@...co.com>
To:	Prabhakar Lad <prabhakar.lad@...com>
Cc:	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	LMML <linux-media@...r.kernel.org>,
	dlos <davinci-linux-open-source@...ux.davincidsp.com>,
	linux-kernel@...r.kernel.org,
	Manjunath Hadli <manjunath.hadli@...com>,
	linux-doc@...r.kernel.org, Hans Verkuil <hans.verkuil@...co.com>,
	"Sakari Ailus" <sakari.ailus@....fi>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	Hans de Goede <hdegoede@...hat.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	"Guennadi Liakhovetski" <g.liakhovetski@....de>,
	Rob Landley <rob@...dley.net>
Subject: Re: [PATCH v3] media: v4l2-ctrl: add a helper function to modify the menu

On Thu 13 September 2012 13:43:36 Prabhakar Lad wrote:
> Hi Laurent,
> 
> Thanks for the review.
> 
> On Thursday 13 September 2012 06:45 AM, Laurent Pinchart wrote:
> > Hi Prabhakar,
> > 
> > Thanks for the patch.
> > 
> > On Tuesday 11 September 2012 19:53:38 Prabhakar Lad wrote:
> >> From: Lad, Prabhakar <prabhakar.lad@...com>
> >>
> >> Add a helper function to modify the menu, max and default value
> >> to set.
> >>
> >> Signed-off-by: Lad, Prabhakar <prabhakar.lad@...com>
> >> Signed-off-by: Manjunath Hadli <manjunath.hadli@...com>
> >> Cc: Hans Verkuil <hans.verkuil@...co.com>
> >> Cc: Sakari Ailus <sakari.ailus@....fi>
> >> Cc: Sylwester Nawrocki <s.nawrocki@...sung.com>
> >> Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> >> Cc: Mauro Carvalho Chehab <mchehab@...radead.org>
> >> Cc: Hans de Goede <hdegoede@...hat.com>
> >> Cc: Kyungmin Park <kyungmin.park@...sung.com>
> >> Cc: Guennadi Liakhovetski <g.liakhovetski@....de>
> >> Cc: Rob Landley <rob@...dley.net>
> >> ---
> >> Changes for v3:
> >> 1: Fixed style/grammer issues as pointed by Hans.
> >>    Thanks Hans for providing the description.
> >>
> >> Changes for v2:
> >> 1: Fixed review comments from Hans, to have return type as
> >>    void, add WARN_ON() for fail conditions, allow this fucntion
> >>    to modify the menu of custom controls.
> >>
> >>  Documentation/video4linux/v4l2-controls.txt |   29 ++++++++++++++++++++++++
> >>  drivers/media/v4l2-core/v4l2-ctrls.c        |   17 +++++++++++++++
> >>  include/media/v4l2-ctrls.h                  |   11 ++++++++++
> >>  3 files changed, 57 insertions(+), 0 deletions(-)
> >>
> >> diff --git a/Documentation/video4linux/v4l2-controls.txt
> >> b/Documentation/video4linux/v4l2-controls.txt index 43da22b..01d0a82 100644
> >> --- a/Documentation/video4linux/v4l2-controls.txt
> >> +++ b/Documentation/video4linux/v4l2-controls.txt
> >> @@ -367,6 +367,35 @@ it to 0 means that all menu items are supported.
> >>  You set this mask either through the v4l2_ctrl_config struct for a custom
> >>  control, or by calling v4l2_ctrl_new_std_menu().
> >>
> >> +There are situations where menu items may be device specific. In such cases
> >> the
> >> +framework provides a helper function to change the menu:
> >> +
> >> +void v4l2_ctrl_modify_menu(struct v4l2_ctrl *ctrl, const char * const
> >> *qmenu,
> >> +	s32 max, u32 menu_skip_mask, s32 def);
> > 
> > Sorry if this is a stupid question, but wouldn't it be better to add a 
> > function to create a custom menu instead of modifying it afterwards ?
> > 
> Create a custom menu? eventually everything boils down to modifying the
> menu itself.

Laurent, the reason we went for modifying a standard control is that that
ensures that the control name and type is all standardized. The only thing
that can be changed later is the menu contents.

Regards,

	Hans

> 
> Regards,
> --Prabhakar Lad
> 
> >> +
> >> +A good example is the test pattern control for capture/display/sensors
> >> devices
> >> +that have the capability to generate test patterns. These test patterns are
> >> +hardware specific, so the contents of the menu will vary from device to
> >> device.
> >> +
> >> +This helper function is used to modify the menu, max, mask and the default
> >> +value of the control.
> >> +
> >> +Example:
> >> +
> >> +	static const char * const test_pattern[] = {
> >> +		"Disabled",
> >> +		"Vertical Bars",
> >> +		"Solid Black",
> >> +		"Solid White",
> >> +		NULL,
> >> +	};
> >> +	struct v4l2_ctrl *test_pattern_ctrl =
> >> +		v4l2_ctrl_new_std_menu(&foo->ctrl_handler, &foo_ctrl_ops,
> >> +			V4L2_CID_TEST_PATTERN, V4L2_TEST_PATTERN_DISABLED, 0,
> >> +			V4L2_TEST_PATTERN_DISABLED);
> >> +
> >> +	v4l2_ctrl_modify_menu(test_pattern_ctrl, test_pattern, 3, 0,
> >> +		V4L2_TEST_PATTERN_DISABLED);
> >>
> >>  Custom Controls
> >>  ===============
> > 
> 
> 
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