Re: [PATCH RFC v2 05/37] drm/connector: hdmi: Add output BPC to the connector state

From: Jani Nikula <jani.nikula@linux.intel.com>
To: Pekka Paalanen <ppaalanen@gmail.com>, Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>,
	Emma Anholt <emma@anholt.net>, Jonathan Corbet <corbet@lwn.net>,
	linux-kernel@vger.kernel.org,
	Samuel Holland <samuel@sholland.org>,
	Sandy Huang <hjc@rock-chips.com>,
	Jernej Skrabec <jernej.skrabec@gmail.com>,
	linux-doc@vger.kernel.org, Hans Verkuil <hverkuil@xs4all.nl>,
	linux-rockchip@lists.infradead.org, Chen-Yu Tsai <wens@csie.org>,
	dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org,
	linux-sunxi@lists.linux.dev,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH RFC v2 05/37] drm/connector: hdmi: Add output BPC to the connector state
Date: Thu, 21 Sep 2023 11:56:08 +0300	[thread overview]
Message-ID: <87zg1fq507.fsf@intel.com> (raw)
In-Reply-To: <20230921114845.7edb1d37@eldfell>

On Thu, 21 Sep 2023, Pekka Paalanen <ppaalanen@gmail.com> wrote:
> On Wed, 20 Sep 2023 16:35:20 +0200
> Maxime Ripard <mripard@kernel.org> wrote:
>
>> We'll add automatic selection of the output BPC in a following patch,
>> but let's add it to the HDMI connector state already.
>> 
>> Signed-off-by: Maxime Ripard <mripard@kernel.org>
>> ---
>>  drivers/gpu/drm/drm_atomic.c              |  4 +++-
>>  drivers/gpu/drm/drm_atomic_state_helper.c |  6 +++++-
>>  drivers/gpu/drm/drm_connector.c           | 13 ++++++++++++-
>>  include/drm/drm_connector.h               | 13 ++++++++++++-
>>  4 files changed, 32 insertions(+), 4 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
>> index b1b56dcaa76b..8dce0a2f2ac3 100644
>> --- a/drivers/gpu/drm/drm_atomic.c
>> +++ b/drivers/gpu/drm/drm_atomic.c
>> @@ -1143,9 +1143,11 @@ static void drm_atomic_connector_print_state(struct drm_printer *p,
>>  	drm_printf(p, "\tcolorspace=%s\n", drm_get_colorspace_name(state->colorspace));
>>  
>>  	if (connector->connector_type == DRM_MODE_CONNECTOR_HDMIA ||
>> -	    connector->connector_type == DRM_MODE_CONNECTOR_HDMIB)
>> +	    connector->connector_type == DRM_MODE_CONNECTOR_HDMIB) {
>>  		drm_printf(p, "\tbroadcast_rgb=%s\n",
>>  			   drm_hdmi_connector_get_broadcast_rgb_name(state->hdmi.broadcast_rgb));
>> +		drm_printf(p, "\toutput_bpc=%u\n", state->hdmi.output_bpc);
>> +	}
>>  
>>  	if (connector->connector_type == DRM_MODE_CONNECTOR_WRITEBACK)
>>  		if (state->writeback_job && state->writeback_job->fb)
>> diff --git a/drivers/gpu/drm/drm_atomic_state_helper.c b/drivers/gpu/drm/drm_atomic_state_helper.c
>> index 0f7e5ba555b8..2c9b52ae1b56 100644
>> --- a/drivers/gpu/drm/drm_atomic_state_helper.c
>> +++ b/drivers/gpu/drm/drm_atomic_state_helper.c
>> @@ -569,6 +569,9 @@ EXPORT_SYMBOL(drm_atomic_helper_connector_tv_reset);
>>  void __drm_atomic_helper_connector_hdmi_reset(struct drm_connector *connector,
>>  					      struct drm_connector_state *new_state)
>>  {
>> +	new_state->max_bpc = 8;
>> +	new_state->max_requested_bpc = 8;
>> +	new_state->hdmi.output_bpc = 8;
>
> Hi,
>
> will this be forcing all drivers using these helpers to default to max bpc = 8?
>
> I believe at least amdgpu would disagree. The defaults were changed in
> the recent years, IIRC to avoid extra modesets during boot-up when
> desktops prefer highest possible bpc for a mode.
>
> The 'max bpc' property itself is a manual workaround for faulty
> hardware that does not correctly indicate the max bpc it can handle. It
> should not default to be a limiting factor.
>
>>  	new_state->hdmi.broadcast_rgb = DRM_HDMI_BROADCAST_RGB_AUTO;
>>  }
>>  EXPORT_SYMBOL(__drm_atomic_helper_connector_hdmi_reset);
>> @@ -651,7 +654,8 @@ int drm_atomic_helper_connector_hdmi_check(struct drm_connector *connector,
>>  	struct drm_connector_state *new_state =
>>  		drm_atomic_get_new_connector_state(state, connector);
>>  
>> -	if (old_state->hdmi.broadcast_rgb != new_state->hdmi.broadcast_rgb) {
>> +	if (old_state->hdmi.broadcast_rgb != new_state->hdmi.broadcast_rgb ||
>> +	    old_state->hdmi.output_bpc != new_state->hdmi.output_bpc) {
>>  		struct drm_crtc *crtc = new_state->crtc;
>>  		struct drm_crtc_state *crtc_state;
>>  
>> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
>> index b45471d540ac..f55f5918411c 100644
>> --- a/drivers/gpu/drm/drm_connector.c
>> +++ b/drivers/gpu/drm/drm_connector.c
>> @@ -459,6 +459,7 @@ EXPORT_SYMBOL(drmm_connector_init);
>>   * @funcs: callbacks for this connector
>>   * @connector_type: user visible type of the connector
>>   * @ddc: optional pointer to the associated ddc adapter
>> + * @max_bpc: Maximum bits per char the HDMI connector supports
>>   *
>>   * Initialises a preallocated HDMI connector. Connectors can be
>>   * subclassed as part of driver connector objects.
>> @@ -475,7 +476,8 @@ int drmm_connector_hdmi_init(struct drm_device *dev,
>>  			     struct drm_connector *connector,
>>  			     const struct drm_connector_funcs *funcs,
>>  			     int connector_type,
>> -			     struct i2c_adapter *ddc)
>> +			     struct i2c_adapter *ddc,
>> +			     unsigned int max_bpc)
>>  {
>>  	int ret;
>>  
>> @@ -487,6 +489,15 @@ int drmm_connector_hdmi_init(struct drm_device *dev,
>>  	if (ret)
>>  		return ret;
>>  
>> +	if (max_bpc) {
>> +		if (!(max_bpc == 8 || max_bpc == 10 || max_bpc == 12))
>> +			return -EINVAL;
>> +
>> +		drm_connector_attach_hdr_output_metadata_property(connector);
>> +		drm_connector_attach_max_bpc_property(connector, 8, max_bpc);
>> +		connector->max_bpc = max_bpc;
>> +	}
>> +
>>  	return 0;
>>  }
>>  EXPORT_SYMBOL(drmm_connector_hdmi_init);
>> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
>> index fdcf64ab91a9..d0bcb835c857 100644
>> --- a/include/drm/drm_connector.h
>> +++ b/include/drm/drm_connector.h
>> @@ -1056,6 +1056,11 @@ struct drm_connector_state {
>>  		 * Broadcast RGB selection value.
>>  		 */
>>  		enum drm_hdmi_broadcast_rgb broadcast_rgb;
>> +
>> +		/**
>> +		 * @output_bpc: Bits per character to output.
>
> Is it not bits per channel?

Or component. Or color. Or color channel. ;)

But character I've never heard.

BR,
Jani.

>
>> +		 */
>> +		unsigned int output_bpc;
>>  	} hdmi;
>>  };
>>  
>> @@ -1700,6 +1705,11 @@ struct drm_connector {
>>  	 */
>>  	struct drm_property_blob *path_blob_ptr;
>>  
>> +	/**
>> +	 * @max_bpc: Maximum bits per character the connector supports.
>
> channel?
>
>> +	 */
>> +	unsigned int max_bpc;
>> +
>>  	/**
>>  	 * @max_bpc_property: Default connector property for the max bpc to be
>>  	 * driven out of the connector.
>> @@ -1939,7 +1949,8 @@ int drmm_connector_hdmi_init(struct drm_device *dev,
>>  			     struct drm_connector *connector,
>>  			     const struct drm_connector_funcs *funcs,
>>  			     int connector_type,
>> -			     struct i2c_adapter *ddc);
>> +			     struct i2c_adapter *ddc,
>> +			     unsigned int max_bpc);
>>  void drm_connector_attach_edid_property(struct drm_connector *connector);
>>  int drm_connector_register(struct drm_connector *connector);
>>  void drm_connector_unregister(struct drm_connector *connector);
>> 
>
> Thanks,
> pq

-- 
Jani Nikula, Intel

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