linux-kernel - Re: [PATCH 06/20] lib: Add video format information library

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Message-ID: <6b4d5c3bd1a6f58ce21bc79518e72ec00a1eed97.camel@bootlin.com>
Date:   Wed, 17 Apr 2019 16:03:08 +0200
From:   Paul Kocialkowski <paul.kocialkowski@...tlin.com>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     Daniel Vetter <daniel.vetter@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Sean Paul <seanpaul@...omium.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org
Subject: Re: [PATCH 06/20] lib: Add video format information library

Hi,

On Wed, 2019-04-17 at 14:48 +0200, Maxime Ripard wrote:
> Hi,
> 
> On Wed, Apr 17, 2019 at 02:34:54PM +0200, Paul Kocialkowski wrote:
> > > +struct image_format_info {
> > > +	union {
> > > +		/**
> > > +		 * @drm_fmt:
> > > +		 *
> > > +		 * DRM 4CC format identifier (DRM_FORMAT_*)
> > > +		 */
> > > +		u32 drm_fmt;
> > 
> > Could we call this one format_drm for consistency with the one below?
> 
> The deprecated "format" field will go away at some point, so I'm not
> sure the consistency is an argument there.

Fair enough then. My point was mostly about format vs fmt, so one
option could be to use "compat_fmt" or such, but do whatever you feel
is right, I don't care too much about it.

> > > +/**
> > > + * image_format_info_min_pitch - computes the minimum required pitch in bytes
> > > + * @info: pixel format info
> > > + * @plane: plane index
> > > + * @buffer_width: buffer width in pixels
> > > + *
> > > + * Returns:
> > > + * The minimum required pitch in bytes for a buffer by taking into consideration
> > > + * the pixel format information and the buffer width.
> > > + */
> > > +static inline
> > > +uint64_t image_format_info_min_pitch(const struct image_format_info *info,
> > > +				     int plane, unsigned int buffer_width)
> > > +{
> > > +	if (!info || plane < 0 || plane >= info->num_planes)
> > > +		return 0;
> > > +
> > > +	return DIV_ROUND_UP_ULL((u64)buffer_width * info->char_per_block[plane],
> > > +			    image_format_info_block_width(info, plane) *
> > > +			    image_format_info_block_height(info, plane));
> > 
> > I'm not sure I understand how this works: char_per_block is 0 for
> > almost all formats and this doesn't take in account the cpp. Am I
> > missing something here?
> 
> I guess it doesn't. That's the DRM function here, without any
> modification, but from a quick look at the current users of that
> function, there's nobody that uses the value directly.
> 
> So you might be right there.
>
> > Also, this might be a good occasion to discuss what meaning we want to
> > give "stride" and "pitch": should one be in bytes and the other in bit,
> > etc? I keep forgetting what each API expects.
> 
> pitch is documented as bytes, and the function computing the stride I
> added did too. I'll remove the stride one.

Okay, it seems that I was just confused for no particular reason and
stride, pitch, bytesperline and linesize are all just synonyms. So feel
free to pick whichever you see fit :) 

Cheers,

Paul

-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com