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Message-ID: <806f2ad3-c80b-41e5-9388-f1af7bace8e3@xs4all.nl>
Date:   Fri, 3 Nov 2023 10:05:18 +0100
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Subject: Re: [PATCH RFC v3 12/37] drm/connector: hdmi: Create Infoframe
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To:     Maxime Ripard <mripard@kernel.org>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>, Emma Anholt <emma@anholt.net>,
        Jonathan Corbet <corbet@lwn.net>,
        Sandy Huang <hjc@rock-chips.com>,
        =?UTF-8?Q?Heiko_St=C3=BCbner?= <heiko@sntech.de>,
        Chen-Yu Tsai <wens@csie.org>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        Samuel Holland <samuel@sholland.org>
Cc:     dri-devel@lists.freedesktop.org,
        linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
        linux-rockchip@lists.infradead.org, linux-sunxi@lists.linux.dev
References: <20231031-kms-hdmi-connector-state-v3-0-328b0fae43a7@kernel.org>
 <20231031-kms-hdmi-connector-state-v3-12-328b0fae43a7@kernel.org>
From:   Hans Verkuil <hverkuil@xs4all.nl>
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In-Reply-To: <20231031-kms-hdmi-connector-state-v3-12-328b0fae43a7@kernel.org>
Content-Type: text/plain; charset=UTF-8
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Precedence: bulk

Hi Maxime,

Thank you for posting v3, this time it runs fine on my RPi 4, thank you for
fixing that.

I'll start working on a conformity checker for this.

I have a few remarks:

On 31/10/2023 17:48, Maxime Ripard wrote:
> There has been some discussions recently about the infoframes sent by
> drivers and if they were properly generated.
> 
> In parallel, there's been some interest in creating an infoframe-decode
> tool similar to edid-decode.
> 
> Both would be much easier if we were to expose the infoframes programmed
> in the hardware. It won't be perfect since we have no guarantee that
> it's actually what goes through the wire, but it's the best we can do.
> 
> Signed-off-by: Maxime Ripard <mripard@kernel.org>
> ---
>  drivers/gpu/drm/drm_debugfs.c | 110 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 110 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_debugfs.c b/drivers/gpu/drm/drm_debugfs.c
> index 2de43ff3ce0a..3c65b1d3f926 100644
> --- a/drivers/gpu/drm/drm_debugfs.c
> +++ b/drivers/gpu/drm/drm_debugfs.c
> @@ -538,6 +538,114 @@ static const struct file_operations drm_connector_fops = {
>  	.write = connector_write
>  };
>  
> +struct debugfs_wrapper {
> +	struct drm_connector *connector;
> +	struct drm_connector_hdmi_infoframe *frame;
> +};
> +
> +#define HDMI_MAX_INFOFRAME_SIZE		29
> +
> +static ssize_t
> +infoframe_read(struct file *filp, char __user *ubuf, size_t count, loff_t *ppos)
> +{
> +	const struct debugfs_wrapper *wrapper = filp->private_data;
> +	struct drm_connector *connector = wrapper->connector;
> +	struct drm_connector_hdmi_infoframe *infoframe = wrapper->frame;
> +	union hdmi_infoframe *frame = &infoframe->data;
> +	u8 buf[HDMI_MAX_INFOFRAME_SIZE];
> +	ssize_t len = 0;
> +
> +	mutex_lock(&connector->hdmi.infoframes.lock);
> +
> +	if (!infoframe->set)
> +		goto out;
> +
> +	len = hdmi_infoframe_pack(frame, buf, sizeof(buf));
> +	if (len < 0)
> +		goto out;
> +
> +	len = simple_read_from_buffer(ubuf, count, ppos, buf, len);
> +
> +out:
> +	mutex_unlock(&connector->hdmi.infoframes.lock);
> +	return len;
> +}
> +
> +static const struct file_operations infoframe_fops = {
> +	.owner   = THIS_MODULE,
> +	.open    = simple_open,
> +	.read    = infoframe_read,
> +};
> +
> +static int create_hdmi_infoframe_file(struct drm_connector *connector,
> +				      struct dentry *parent,
> +				      const char *filename,
> +				      struct drm_connector_hdmi_infoframe *frame)
> +{
> +	struct drm_device *dev = connector->dev;
> +	struct debugfs_wrapper *wrapper;
> +	struct dentry *file;
> +
> +	wrapper = drmm_kzalloc(dev, sizeof(*wrapper), GFP_KERNEL);
> +	if (!wrapper)
> +		return -ENOMEM;
> +
> +	wrapper->connector = connector;
> +	wrapper->frame = frame;
> +
> +	file = debugfs_create_file(filename, 0400, parent, wrapper, &infoframe_fops);
> +	if (IS_ERR(file))
> +		return PTR_ERR(file);
> +
> +	return 0;
> +}
> +
> +#define CREATE_HDMI_INFOFRAME_FILE(c, p, i)		\
> +	create_hdmi_infoframe_file(c, p, #i, &(c)->hdmi.infoframes.i)
> +
> +static int create_hdmi_infoframe_files(struct drm_connector *connector,
> +				       struct dentry *parent)
> +{
> +	int ret;
> +
> +	ret = CREATE_HDMI_INFOFRAME_FILE(connector, parent, audio);
> +	if (ret)
> +		return ret;
> +
> +	ret = CREATE_HDMI_INFOFRAME_FILE(connector, parent, avi);
> +	if (ret)
> +		return ret;
> +
> +	ret = CREATE_HDMI_INFOFRAME_FILE(connector, parent, drm);

Hmm, I had to look into the code to figure out that 'drm' stands for
Dynamic Range and Mastering InfoFrame. While entirely correct, it is
also very confusing in the context of the 'drm' subsystem.

I am not quite certain what the best approach is here.

Internally in the drm code it is talking about 'hdr' or 'hdr metadata',
but that's a bit confusing as well since there is also an HDR Dynamic
Metadata Extended InfoFrame defined in CTA-861, even though support for
that is not (yet) implemented in drm.

At minimum there should be a comment in the code explaining what drm
stands for in this context.

One option to consider is renaming this file to hdr_drm, thus indicating
that this is HDR related.

> +	if (ret)
> +		return ret;
> +
> +	ret = CREATE_HDMI_INFOFRAME_FILE(connector, parent, spd);
> +	if (ret)
> +		return ret;
> +
> +	ret = CREATE_HDMI_INFOFRAME_FILE(connector, parent, vendor);

There may be multiple vendor specific InfoFrames in the future, so how
would that be handled? Perhaps add a comment here that currently only one
vendor specific InfoFrame is supported, but suggest how to handle multiple
VSIFs in the future.

What would actually be nice (although probably not that easy to fix) is if
the name of the file would be "vendor-XXXXXX' where 'XXXXXX' is the IEEE OUI
number.

Regards,

	Hans

> +	if (ret)
> +		return ret;
> +
> +	return 0;
> +}
> +
> +static void hdmi_debugfs_add(struct drm_connector *connector)
> +{
> +	struct dentry *dir;
> +
> +	if (!(connector->connector_type == DRM_MODE_CONNECTOR_HDMIA ||
> +	      connector->connector_type == DRM_MODE_CONNECTOR_HDMIB))
> +		return;
> +
> +	dir = debugfs_create_dir("infoframes", connector->debugfs_entry);
> +	if (IS_ERR(dir))
> +		return;
> +
> +	create_hdmi_infoframe_files(connector, dir);
> +}
> +
>  void drm_debugfs_connector_add(struct drm_connector *connector)
>  {
>  	struct drm_minor *minor = connector->dev->primary;
> @@ -565,6 +673,8 @@ void drm_debugfs_connector_add(struct drm_connector *connector)
>  	debugfs_create_file("output_bpc", 0444, root, connector,
>  			    &output_bpc_fops);
>  
> +	hdmi_debugfs_add(connector);
> +
>  	if (connector->funcs->debugfs_init)
>  		connector->funcs->debugfs_init(connector, root);
>  }
>