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

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Message-ID: <20190417124833.psdri6laune5y2ti@flea>
Date:   Wed, 17 Apr 2019 14:48:33 +0200
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Paul Kocialkowski <paul.kocialkowski@...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, 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.

> > +/**
> > + * 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.

Maxime

--
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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