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From:   Ayan Halder <Ayan.Halder@arm.com>
To:     Brian Starkey <Brian.Starkey@arm.com>
CC:     "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>,
        nd <nd@arm.com>,
        "james qian wang (Arm Technology China)" <james.qian.wang@arm.com>,
        Liviu Dudau <Liviu.Dudau@arm.com>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3] drm/crc-debugfs: Add notes about CRC<->commit
 interactions
Thread-Topic: [PATCH v3] drm/crc-debugfs: Add notes about CRC<->commit
 interactions
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Date:   Wed, 7 Aug 2019 13:01:54 +0000
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On Tue, Aug 06, 2019 at 01:46:22PM +0100, Brian Starkey wrote:
> CRC generation can be impacted by commits coming from userspace, and
> enabling CRC generation may itself trigger a commit. Add notes about
> this to the kerneldoc.
>=20
> Changes since v1:
>  - Clarified that anything that would disable CRCs counts as a full
>    modeset, and so userspace needs to reconfigure after full modesets
>=20
> Changes since v2:
>  - Add these notes
>  - Rebase onto drm-misc-next (trivial conflict in comment)
>=20
> Signed-off-by: Brian Starkey <brian.starkey@arm.com>
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>  drivers/gpu/drm/drm_debugfs_crc.c | 9 +++++++++
>  include/drm/drm_crtc.h            | 4 ++++
>  2 files changed, 13 insertions(+)
>=20
> diff --git a/drivers/gpu/drm/drm_debugfs_crc.c b/drivers/gpu/drm/drm_debu=
gfs_crc.c
> index 6604ed223160..be1b7ba92ffe 100644
> --- a/drivers/gpu/drm/drm_debugfs_crc.c
> +++ b/drivers/gpu/drm/drm_debugfs_crc.c
> @@ -69,6 +69,15 @@
>   * implement &drm_crtc_funcs.set_crc_source and &drm_crtc_funcs.verify_c=
rc_source.
>   * The debugfs files are automatically set up if those vfuncs are set. C=
RC samples
>   * need to be captured in the driver by calling drm_crtc_add_crc_entry()=
.
> + * Depending on the driver and HW requirements, &drm_crtc_funcs.set_crc_=
source
> + * may result in a commit (even a full modeset).
> + *
> + * CRC results must be reliable across non-full-modeset atomic commits, =
so if a
> + * commit via DRM_IOCTL_MODE_ATOMIC would disable or otherwise interfere=
 with
> + * CRC generation, then the driver must mark that commit as a full modes=
et
> + * (drm_atomic_crtc_needs_modeset() should return true). As a result, to=
 ensure
> + * consistent results, generic userspace must re-setup CRC generation af=
ter a
> + * legacy SETCRTC or an atomic commit with DRM_MODE_ATOMIC_ALLOW_MODESET=
.
>   */
> =20
>  static int crc_control_show(struct seq_file *m, void *data)
> diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
> index 128d8b210621..7d14c11bdc0a 100644
> --- a/include/drm/drm_crtc.h
> +++ b/include/drm/drm_crtc.h
> @@ -756,6 +756,9 @@ struct drm_crtc_funcs {
>  	 * provided from the configured source. Drivers must accept an "auto"
>  	 * source name that will select a default source for this CRTC.
>  	 *
> +	 * This may trigger an atomic modeset commit if necessary, to enable CR=
C
> +	 * generation.
> +	 *
>  	 * Note that "auto" can depend upon the current modeset configuration,
>  	 * e.g. it could pick an encoder or output specific CRC sampling point.
>  	 *
> @@ -767,6 +770,7 @@ struct drm_crtc_funcs {
>  	 * 0 on success or a negative error code on failure.
>  	 */
>  	int (*set_crc_source)(struct drm_crtc *crtc, const char *source);
> +
>  	/**
>  	 * @verify_crc_source:
>  	 *
> --=20
> 2.17.1
>=20

Pushed to drm-misc-next.
Commit id :- 178e5f3a5bc1d67d1248a74c0abab41040abe7c4

-Ayan
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