Message-ID: <CA+hFU4zKxwB-WLw7LEGjSShG0LmpPGTcJRTCADU5V4unkfaZOQ@mail.gmail.com>
Date:   Tue, 21 Feb 2023 12:38:12 +0100
From:   Sebastian Wick <sebastian.wick@...hat.com>
To:     Dave Stevenson <dave.stevenson@...pberrypi.com>
Cc:     Hans Verkuil <hverkuil@...all.nl>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Emma Anholt <emma@...olt.net>, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, Maxime Ripard <maxime@...no.tech>
Subject: Re: [PATCH v2 3/9] drm/vc4: hdmi: Add Broadcast RGB property to allow
 override of RGB range

On Mon, Feb 20, 2023 at 4:24 PM Dave Stevenson
<dave.stevenson@...pberrypi.com> wrote:
>
> Hi Hans
>
> On Sat, 18 Feb 2023 at 11:33, Hans Verkuil <hverkuil@...all.nl> wrote:
> >
> > Hi Maxime, Dave,
> >
> > On 26/01/2023 14:46, Maxime Ripard wrote:
> > > From: Dave Stevenson <dave.stevenson@...pberrypi.com>
> > >
> > > Copy Intel's "Broadcast RGB" property semantics to add manual override
> > > of the HDMI pixel range for monitors that don't abide by the content
> > > of the AVI Infoframe.
> >
> > Do we have to copy that property as-is?
>
> Firstly I'll agree with your later comment that having this control
> allows testing of a range of output modes, and working around HDMI
> sinks that have dodgy implementations.
> (In our vendor kernel we now also have a property to override the
> kernel chosen output format to enable testing of YCbCr4:4:4 and 4:2:2
> output).
>
> The DRM subsystem has the requirement for an open-source userspace
> project to be using any new property before it will be merged [1].
> This property already exists for i915 and gma-500, therefore avoids
> that requirement.
>
> There are objections to the UAPI for Broadcast RGB [2], but if it's
> good enough for the existing implementations then there can be no
> objection to it being implemented in the same way for other drivers.
> Otherwise it is a missing feature of the DRM API, and the linked
> discussion is realistically at least a year away from being resolved.
> Why bury our heads in the sand for that period?
>
> [1] https://dri.freedesktop.org/docs/drm/gpu/drm-uapi.html#open-source-userspace-requirements
> [2] https://lists.freedesktop.org/archives/dri-devel/2023-February/391061.html

FWIW, from a user space perspective I'm still very much in favor of
adding the `Broadcast RGB` property to more drivers and even moving it
to drm core. Splitting things into color pipeline control properties
and infoframe/connector properties is much harder than it seems at
first and IMO needs a more holistic approach that you can't get from
just converting the one property.

>
> > First of all, I think this should really be a drm-level property, rather than
> > a driver property: RGB Quantization Range mismatches are the bane of my life,
> > and I think a way to override this would help everyone.
>
> Linked to above, if it were the preferred method for controlling this
> then I would expect it to become a drm-level property.
>
> > Secondly, I hate the name they came up with: 'Broadcast RGB' is pretty meaningless.
> > Can't we stick to something closer to what the CTA-861/HDMI specs use, which is
> > 'RGB Quantization Range'? So either use that, or just 'RGB Range'.
> >
> > In addition, 'Limited 16:235' should just be 'Limited' since the actual range
> > depends on the bits-per-color-component.
>
> It's documented UAPI with those names[3], therefore any change would
> be a change to user-space's expectation and a regression. At least by
> sticking with the same names then any user space implementation that
> exists for i915 or gma-500 will also work in the same way on vc4.
>
> [3] https://www.kernel.org/doc/html/latest/gpu/drm-kms.html#existing-kms-properties
>
> > >
> > > Signed-off-by: Dave Stevenson <dave.stevenson@...pberrypi.com>
> > > Signed-off-by: Maxime Ripard <maxime@...no.tech>
> > > ---
> > >  drivers/gpu/drm/vc4/vc4_hdmi.c | 97 ++++++++++++++++++++++++++++++++++++++++--
> > >  drivers/gpu/drm/vc4/vc4_hdmi.h |  9 ++++
> > >  2 files changed, 102 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> > > index 4b3bf77bb5cd..78749c6fa837 100644
> > > --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> > > +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> > > @@ -150,10 +150,16 @@ static bool vc4_hdmi_mode_needs_scrambling(const struct drm_display_mode *mode,
> > >  }
> > >
> > >  static bool vc4_hdmi_is_full_range_rgb(struct vc4_hdmi *vc4_hdmi,
> > > -                                    const struct drm_display_mode *mode)
> > > +                                    struct vc4_hdmi_connector_state *vc4_state)
> > >  {
> > > +     const struct drm_display_mode *mode = &vc4_hdmi->saved_adjusted_mode;
> > >       struct drm_display_info *display = &vc4_hdmi->connector.display_info;
> > >
> > > +     if (vc4_state->broadcast_rgb == VC4_HDMI_BROADCAST_RGB_LIMITED)
> > > +             return false;
> > > +     else if (vc4_state->broadcast_rgb == VC4_HDMI_BROADCAST_RGB_FULL)
> > > +             return true;
> > > +
> > >       return !display->is_hdmi ||
> > >               drm_default_rgb_quant_range(mode) == HDMI_QUANTIZATION_RANGE_FULL;
> > >  }
> > > @@ -524,8 +530,12 @@ static int vc4_hdmi_connector_atomic_check(struct drm_connector *connector,
> > >  {
> > >       struct drm_connector_state *old_state =
> > >               drm_atomic_get_old_connector_state(state, connector);
> > > +     struct vc4_hdmi_connector_state *old_vc4_state =
> > > +             conn_state_to_vc4_hdmi_conn_state(old_state);
> > >       struct drm_connector_state *new_state =
> > >               drm_atomic_get_new_connector_state(state, connector);
> > > +     struct vc4_hdmi_connector_state *new_vc4_state =
> > > +             conn_state_to_vc4_hdmi_conn_state(new_state);
> > >       struct drm_crtc *crtc = new_state->crtc;
> > >
> > >       if (!crtc)
> > > @@ -558,6 +568,7 @@ static int vc4_hdmi_connector_atomic_check(struct drm_connector *connector,
> > >       }
> > >
> > >       if (old_state->colorspace != new_state->colorspace ||
> > > +         old_vc4_state->broadcast_rgb != new_vc4_state->broadcast_rgb ||
> >
> > The problem with this is that this will cause a mode change, even though all
> > that is necessary is to update the csc matrix and AVI InfoFrame.
> >
> > I used this code (added just before the 'return 0;' at the end of this function):
> >
> >         if (old_vc4_state->broadcast_rgb != new_vc4_state->broadcast_rgb) {
> >                 const struct drm_display_mode *mode = &vc4_hdmi->saved_adjusted_mode;
> >
> >                 old_vc4_state->broadcast_rgb = new_vc4_state->broadcast_rgb;
> >                 vc4_hdmi_set_avi_infoframe(encoder);
> >                 if (vc4_hdmi->variant->csc_setup)
> >                         vc4_hdmi->variant->csc_setup(vc4_hdmi, old_state, mode);
> >         }
> >
> > I'm certain this is in the wrong place, but I'm not familiar enough with the drm API
> > to determine where this should go.
>
> atomic_check is meant to validate the state, but must never touch the
> hardware [4].
> atomic_commit updates the hardware, although for struct
> drm_connector_helper_funcs atomic_commit is documented as only being
> applicable for writeback connectors [5]. Hence our only sensible
> options are to trigger a mode change which reprograms everything, or
> ignore the helpers.
> There may be scope for improving this, but it'll need significant
> driver (and possibly framework) rework in order to be done properly.
>
> [4] https://elixir.bootlin.com/linux/latest/source/include/drm/drm_modeset_helper_vtables.h#L1083
> [5] https://elixir.bootlin.com/linux/latest/source/include/drm/drm_modeset_helper_vtables.h#L1101
>
> > This approach probably applies to the hdr_metadata metadata as well, that too
> > doesn't need a mode change.
> >
> > I see that the i915 driver has a 'fastset' mechanism for changes like this, but
> > it is not clear to me how that interacts with the drm API.
> >
> > I've been playing around with this vc4 driver and it is proving to be very useful
> > for debugging all sorts of quantization range bugs in other equipment.
>
> Glad it's proving useful.
>
> We're also needing it as users have misbehaving monitors, and telling
> them to replace the monitor as it breaks the HDMI spec generally
> doesn't go down well! Likewise I've had users needing YCbCr444 output
> because of some limitation in their receiving device, hence overriding
> the kernel choice of output mode. It'd be nice if there were consensus
> on the correct way to achieve that.
>
> Cheers.
>   Dave
>
> > Regards,
> >
> >         Hans
> >
> > >           !drm_connector_atomic_hdr_metadata_equal(old_state, new_state)) {
> > >               struct drm_crtc_state *crtc_state;
> > >
> > > @@ -571,6 +582,49 @@ static int vc4_hdmi_connector_atomic_check(struct drm_connector *connector,
> > >       return 0;
> > >  }
> > >
> > > +static int vc4_hdmi_connector_get_property(struct drm_connector *connector,
> > > +                                        const struct drm_connector_state *state,
> > > +                                        struct drm_property *property,
> > > +                                        uint64_t *val)
> > > +{
> > > +     struct drm_device *drm = connector->dev;
> > > +     struct vc4_hdmi *vc4_hdmi =
> > > +             connector_to_vc4_hdmi(connector);
> > > +     const struct vc4_hdmi_connector_state *vc4_conn_state =
> > > +             conn_state_to_vc4_hdmi_conn_state(state);
> > > +
> > > +     if (property == vc4_hdmi->broadcast_rgb_property) {
> > > +             *val = vc4_conn_state->broadcast_rgb;
> > > +     } else {
> > > +             drm_dbg(drm, "Unknown property [PROP:%d:%s]\n",
> > > +                     property->base.id, property->name);
> > > +             return -EINVAL;
> > > +     }
> > > +
> > > +     return 0;
> > > +}
> > > +
> > > +static int vc4_hdmi_connector_set_property(struct drm_connector *connector,
> > > +                                        struct drm_connector_state *state,
> > > +                                        struct drm_property *property,
> > > +                                        uint64_t val)
> > > +{
> > > +     struct drm_device *drm = connector->dev;
> > > +     struct vc4_hdmi *vc4_hdmi =
> > > +             connector_to_vc4_hdmi(connector);
> > > +     struct vc4_hdmi_connector_state *vc4_conn_state =
> > > +             conn_state_to_vc4_hdmi_conn_state(state);
> > > +
> > > +     if (property == vc4_hdmi->broadcast_rgb_property) {
> > > +             vc4_conn_state->broadcast_rgb = val;
> > > +             return 0;
> > > +     }
> > > +
> > > +     drm_dbg(drm, "Unknown property [PROP:%d:%s]\n",
> > > +             property->base.id, property->name);
> > > +     return -EINVAL;
> > > +}
> > > +
> > >  static void vc4_hdmi_connector_reset(struct drm_connector *connector)
> > >  {
> > >       struct vc4_hdmi_connector_state *old_state =
> > > @@ -590,6 +644,7 @@ static void vc4_hdmi_connector_reset(struct drm_connector *connector)
> > >       new_state->base.max_bpc = 8;
> > >       new_state->base.max_requested_bpc = 8;
> > >       new_state->output_format = VC4_HDMI_OUTPUT_RGB;
> > > +     new_state->broadcast_rgb = VC4_HDMI_BROADCAST_RGB_AUTO;
> > >       drm_atomic_helper_connector_tv_margins_reset(connector);
> > >  }
> > >
> > > @@ -607,6 +662,7 @@ vc4_hdmi_connector_duplicate_state(struct drm_connector *connector)
> > >       new_state->tmds_char_rate = vc4_state->tmds_char_rate;
> > >       new_state->output_bpc = vc4_state->output_bpc;
> > >       new_state->output_format = vc4_state->output_format;
> > > +     new_state->broadcast_rgb = vc4_state->broadcast_rgb;
> > >       __drm_atomic_helper_connector_duplicate_state(connector, &new_state->base);
> > >
> > >       return &new_state->base;
> > > @@ -617,6 +673,8 @@ static const struct drm_connector_funcs vc4_hdmi_connector_funcs = {
> > >       .reset = vc4_hdmi_connector_reset,
> > >       .atomic_duplicate_state = vc4_hdmi_connector_duplicate_state,
> > >       .atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
> > > +     .atomic_get_property = vc4_hdmi_connector_get_property,
> > > +     .atomic_set_property = vc4_hdmi_connector_set_property,
> > >  };
> > >
> > >  static const struct drm_connector_helper_funcs vc4_hdmi_connector_helper_funcs = {
> > > @@ -625,6 +683,33 @@ static const struct drm_connector_helper_funcs vc4_hdmi_connector_helper_funcs =
> > >       .atomic_check = vc4_hdmi_connector_atomic_check,
> > >  };
> > >
> > > +static const struct drm_prop_enum_list broadcast_rgb_names[] = {
> > > +     { VC4_HDMI_BROADCAST_RGB_AUTO, "Automatic" },
> > > +     { VC4_HDMI_BROADCAST_RGB_FULL, "Full" },
> > > +     { VC4_HDMI_BROADCAST_RGB_LIMITED, "Limited 16:235" },
> > > +};
> > > +
> > > +static void
> > > +vc4_hdmi_attach_broadcast_rgb_property(struct drm_device *dev,
> > > +                                    struct vc4_hdmi *vc4_hdmi)
> > > +{
> > > +     struct drm_property *prop = vc4_hdmi->broadcast_rgb_property;
> > > +
> > > +     if (!prop) {
> > > +             prop = drm_property_create_enum(dev, DRM_MODE_PROP_ENUM,
> > > +                                             "Broadcast RGB",
> > > +                                             broadcast_rgb_names,
> > > +                                             ARRAY_SIZE(broadcast_rgb_names));
> > > +             if (!prop)
> > > +                     return;
> > > +
> > > +             vc4_hdmi->broadcast_rgb_property = prop;
> > > +     }
> > > +
> > > +     drm_object_attach_property(&vc4_hdmi->connector.base, prop,
> > > +                                VC4_HDMI_BROADCAST_RGB_AUTO);
> > > +}
> > > +
> > >  static int vc4_hdmi_connector_init(struct drm_device *dev,
> > >                                  struct vc4_hdmi *vc4_hdmi)
> > >  {
> > > @@ -671,6 +756,8 @@ static int vc4_hdmi_connector_init(struct drm_device *dev,
> > >       if (vc4_hdmi->variant->supports_hdr)
> > >               drm_connector_attach_hdr_output_metadata_property(connector);
> > >
> > > +     vc4_hdmi_attach_broadcast_rgb_property(dev, vc4_hdmi);
> > > +
> > >       drm_connector_attach_encoder(connector, encoder);
> > >
> > >       return 0;
> > > @@ -825,7 +912,7 @@ static void vc4_hdmi_set_avi_infoframe(struct drm_encoder *encoder)
> > >
> > >       drm_hdmi_avi_infoframe_quant_range(&frame.avi,
> > >                                          connector, mode,
> > > -                                        vc4_hdmi_is_full_range_rgb(vc4_hdmi, mode) ?
> > > +                                        vc4_hdmi_is_full_range_rgb(vc4_hdmi, vc4_state) ?
> > >                                          HDMI_QUANTIZATION_RANGE_FULL :
> > >                                          HDMI_QUANTIZATION_RANGE_LIMITED);
> > >       drm_hdmi_avi_infoframe_colorimetry(&frame.avi, cstate);
> > > @@ -1066,6 +1153,8 @@ static void vc4_hdmi_csc_setup(struct vc4_hdmi *vc4_hdmi,
> > >                              struct drm_connector_state *state,
> > >                              const struct drm_display_mode *mode)
> > >  {
> > > +     struct vc4_hdmi_connector_state *vc4_state =
> > > +             conn_state_to_vc4_hdmi_conn_state(state);
> > >       struct drm_device *drm = vc4_hdmi->connector.dev;
> > >       unsigned long flags;
> > >       u32 csc_ctl;
> > > @@ -1079,7 +1168,7 @@ static void vc4_hdmi_csc_setup(struct vc4_hdmi *vc4_hdmi,
> > >       csc_ctl = VC4_SET_FIELD(VC4_HD_CSC_CTL_ORDER_BGR,
> > >                               VC4_HD_CSC_CTL_ORDER);
> > >
> > > -     if (!vc4_hdmi_is_full_range_rgb(vc4_hdmi, mode)) {
> > > +     if (!vc4_hdmi_is_full_range_rgb(vc4_hdmi, vc4_state)) {
> > >               /* CEA VICs other than #1 requre limited range RGB
> > >                * output unless overridden by an AVI infoframe.
> > >                * Apply a colorspace conversion to squash 0-255 down
> > > @@ -1232,7 +1321,7 @@ static void vc5_hdmi_csc_setup(struct vc4_hdmi *vc4_hdmi,
> > >       case VC4_HDMI_OUTPUT_RGB:
> > >               if_xbar = 0x354021;
> > >
> > > -             if (!vc4_hdmi_is_full_range_rgb(vc4_hdmi, mode))
> > > +             if (!vc4_hdmi_is_full_range_rgb(vc4_hdmi, vc4_state))
> > >                       vc5_hdmi_set_csc_coeffs(vc4_hdmi, vc5_hdmi_csc_full_rgb_to_limited_rgb);
> > >               else
> > >                       vc5_hdmi_set_csc_coeffs(vc4_hdmi, vc5_hdmi_csc_full_rgb_unity);
> > > diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.h b/drivers/gpu/drm/vc4/vc4_hdmi.h
> > > index 5d249ac54cd1..89800c48aa24 100644
> > > --- a/drivers/gpu/drm/vc4/vc4_hdmi.h
> > > +++ b/drivers/gpu/drm/vc4/vc4_hdmi.h
> > > @@ -117,6 +117,12 @@ enum vc4_hdmi_output_format {
> > >       VC4_HDMI_OUTPUT_YUV420,
> > >  };
> > >
> > > +enum vc4_hdmi_broadcast_rgb {
> > > +     VC4_HDMI_BROADCAST_RGB_AUTO,
> > > +     VC4_HDMI_BROADCAST_RGB_FULL,
> > > +     VC4_HDMI_BROADCAST_RGB_LIMITED,
> > > +};
> > > +
> > >  /* General HDMI hardware state. */
> > >  struct vc4_hdmi {
> > >       struct vc4_hdmi_audio audio;
> > > @@ -129,6 +135,8 @@ struct vc4_hdmi {
> > >
> > >       struct delayed_work scrambling_work;
> > >
> > > +     struct drm_property *broadcast_rgb_property;
> > > +
> > >       struct i2c_adapter *ddc;
> > >       void __iomem *hdmicore_regs;
> > >       void __iomem *hd_regs;
> > > @@ -238,6 +246,7 @@ struct vc4_hdmi_connector_state {
> > >       unsigned long long              tmds_char_rate;
> > >       unsigned int                    output_bpc;
> > >       enum vc4_hdmi_output_format     output_format;
> > > +     enum vc4_hdmi_broadcast_rgb     broadcast_rgb;
> > >  };
> > >
> > >  #define conn_state_to_vc4_hdmi_conn_state(_state)                    \
> > >
> >
>

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