Date:   Thu, 28 Apr 2022 16:04:48 +0200
From:   Dorota Czaplejewicz <dorota.czaplejewicz@...i.sm>
To:     Jacopo Mondi <jacopo@...ndi.org>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...i.sm
Subject: Re: [PATCHv2 2/2] media api: Try to make enum usage clearer

Hi,

On Thu, 28 Apr 2022 15:11:46 +0200
Jacopo Mondi <jacopo@...ndi.org> wrote:

> Hi Dorota
> 
> On Thu, Apr 28, 2022 at 10:52:19AM +0200, Dorota Czaplejewicz wrote:
> > Fixed: typo "format" -> "frame size" in enum-frame-size
> > Added: no holes in the enumeration
> > Added: enumerations per what?
> > Added: who fills in what in calls
> > Changed: "zero" -> "0"
> > Changed: "given" -> "specified"  
> 
> Empty line here
> 
> > Signed-off-by: Dorota Czaplejewicz <dorota.czaplejewicz@...i.sm>
> > ---
> >  .../v4l/vidioc-subdev-enum-frame-size.rst     | 44 ++++++++++++-------
> >  1 file changed, 28 insertions(+), 16 deletions(-)
> >
> > diff --git a/Documentation/userspace-api/media/v4l/vidioc-subdev-enum-frame-size.rst b/Documentation/userspace-api/media/v4l/vidioc-subdev-enum-frame-size.rst
> > index c25a9896df0e..2c6fd291dc44 100644
> > --- a/Documentation/userspace-api/media/v4l/vidioc-subdev-enum-frame-size.rst
> > +++ b/Documentation/userspace-api/media/v4l/vidioc-subdev-enum-frame-size.rst
> > @@ -31,18 +31,29 @@ Arguments
> >  Description
> >  ===========
> >
> > -This ioctl allows applications to enumerate all frame sizes supported by
> > -a sub-device on the given pad for the given media bus format. Supported
> > -formats can be retrieved with the
> > +This ioctl allows applications to access the enumeration of frame sizes supported by  
> 
> over 80 cols
> 
> > +a sub-device on the specified pad for the specified media bus format.
> > +Supported formats can be retrieved with the  
> 
> This seems quite an arbitrary change. What's wrong with the existing
> phrase ?
> 
"Given" is vague and does not really say who gives and who is given.
Is it the kernel or the application? It kept confusing me.
I tried to turn it into a "selected", which has more "application" vibes,
but I was asked to change it to "specified".
IMO this could benefit from an active voice, but I didn't want to rewrite it completely.

About "access the enumeration" - this serves to show the data structure up front.
In my original patch it was "array", which hopefully implies some things:
that it's continuous and indexed.
I was asked to get rid of "array" though.

Thanks,
Dorota
> >  :ref:`VIDIOC_SUBDEV_ENUM_MBUS_CODE`
> >  ioctl.
> >
> > -To enumerate frame sizes applications initialize the ``pad``, ``which``
> > -, ``code`` and ``index`` fields of the struct
> > -:c:type:`v4l2_subdev_mbus_code_enum` and
> > -call the :ref:`VIDIOC_SUBDEV_ENUM_FRAME_SIZE` ioctl with a pointer to the
> > -structure. Drivers fill the minimum and maximum frame sizes or return an
> > -EINVAL error code if one of the input parameters is invalid.
> > +The enumerations are defined by the driver, and indexed using the ``index`` field
> > +of the struct :c:type:`v4l2_subdev_mbus_code_enum`.
> > +Each pair of ``pad`` and ``code`` correspond to a separate enumeration.
> > +Each enumeeration starts with the ``index`` of 0, and  
> 
> s/enumeeration/enumeration/
> 
> > +the lowest invalid index marks the end of the enumeration.
> > +
> > +Therefore, to enumerate frame sizes allowed on the specified pad
> > +and using the specified mbus format, initialize the
> > +``pad``, ``which``, and ``code`` fields to desired values,
> > +and set ``index`` to 0.
> > +Then call the :ref:`VIDIOC_SUBDEV_ENUM_FRAME_SIZE` ioctl with a pointer to the
> > +structure.
> > +
> > +A successful call will return with minimum and maximum frame sizes filled in.
> > +Repeat with increasing ``index`` until ``EINVAL`` is received.
> > +``EINVAL`` means that either no more entries are available in the enumeration,
> > +or that an input parameter was invalid.
> >
> >  Sub-devices that only support discrete frame sizes (such as most
> >  sensors) will return one or more frame sizes with identical minimum and
> > @@ -72,26 +83,27 @@ information about try formats.
> >
> >      * - __u32
> >        - ``index``
> > -      - Number of the format in the enumeration, set by the application.
> > +      - Index of the frame size in the enumeration  
> 
> Rougue line break
> 
> > +    belonging to the given pad and format. Filled in by the application.
> >      * - __u32
> >        - ``pad``
> > -      - Pad number as reported by the media controller API.
> > +      - Pad number as reported by the media controller API. Filled in by the application.  
> 
> over 80 cols
> 
> >      * - __u32
> >        - ``code``
> >        - The media bus format code, as defined in
> > -	:ref:`v4l2-mbus-format`.
> > +	:ref:`v4l2-mbus-format`. Filled in by the application.
> >      * - __u32
> >        - ``min_width``
> > -      - Minimum frame width, in pixels.
> > +      - Minimum frame width, in pixels. Filled in by the driver.
> >      * - __u32
> >        - ``max_width``
> > -      - Maximum frame width, in pixels.
> > +      - Maximum frame width, in pixels. Filled in by the driver.
> >      * - __u32
> >        - ``min_height``
> > -      - Minimum frame height, in pixels.
> > +      - Minimum frame height, in pixels. Filled in by the driver.
> >      * - __u32
> >        - ``max_height``
> > -      - Maximum frame height, in pixels.
> > +      - Maximum frame height, in pixels. Filled in by the driver.
> >      * - __u32
> >        - ``which``
> >        - Frame sizes to be enumerated, from enum  
> 
> Even more than 1/2, I am a bit failing to see what is missing in the
> existing doc. If it feels better to others who will have a look, I for sure
> won't oppose this change though :)
> 
> > --
> > 2.35.1
> >  
> 
> 


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