Re: [Intel-gfx] [PATCH v2 2/2] drm/i915: Add a new debugfs to request HDCP version

[Anshuman Gupta <anshuman.gupta@intel.com>]

On 2020-06-08 at 15:31:03 +0530, Ankit Nautiyal wrote:
> As per the current HDCP design, the driver selects the highest
> version of HDCP that can be used to satisfy the content-protection
> requirements of the user. Due to this, the content-protection
> tests cannot test a lower version of HDCP, if the platform and the
> display panel, both support higher HDCP version.
> 
> To provide some support for testing and debugging, a per-connector
> debugfs is required to set the HDCP version via debugfs that the
> kernel can consider, while enabling HDCP.
> 
> This patch adds a new debugfs entry for each connector that supports
> HDCP. For enforcing a particular HDCP version for a connector, the user
> can write into the debugfs for that connector.
IMHO this doesn't feel like a debugfs per connector, even if it is a
global singleton resource for all connectors, i don't see any problem in
that, may be a global debugfs would make sense here ?
> 
> v2: As suggested by Jani Nikula:
> -used kstrtouint_from_user() to directly read as uint from user buffer.
> -used 32 bit flag instead of 64 bit for hdcp_ver flag.
> -removed unnecessary prints and fixed other minor formatting issues.
> 
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> ---
>  .../drm/i915/display/intel_display_debugfs.c  | 68 +++++++++++++++++++
>  1 file changed, 68 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_display_debugfs.c b/drivers/gpu/drm/i915/display/intel_display_debugfs.c
> index 70525623bcdf..c01653d412e7 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_debugfs.c
> +++ b/drivers/gpu/drm/i915/display/intel_display_debugfs.c
> @@ -2185,6 +2185,72 @@ static const struct file_operations i915_dsc_fec_support_fops = {
>  	.write = i915_dsc_fec_support_write
>  };
>  
> +static int i915_hdcp_ver_request_show(struct seq_file *m, void *data)
> +{
> +	struct drm_connector *connector = m->private;
> +	struct intel_connector *intel_connector = to_intel_connector(connector);
> +	u32 hdcp_ver_flag;
> +
> +	if (connector->status != connector_status_connected)
> +		return -ENODEV;
> +
> +	/* HDCP is supported by connector */
> +	if (!intel_connector->hdcp.shim)
> +		return -EINVAL;
> +
> +	hdcp_ver_flag = intel_connector->hdcp.debugfs_ver_request;
> +	seq_printf(m, "HDCP_VER_FLAGS: %u\n", hdcp_ver_flag);
> +
> +	return 0;
> +}
> +
> +static int i915_hdcp_ver_request_open(struct inode *inode,
> +				      struct file *file)
> +{
> +	return single_open(file, i915_hdcp_ver_request_show,
> +			   inode->i_private);
> +}
> +
> +static ssize_t i915_hdcp_ver_request_write(struct file *file,
> +					   const char __user *ubuf,
> +					   size_t len, loff_t *offp)
> +{
> +	unsigned int hdcp_ver = 0;
> +	int ret;
> +	struct drm_connector *connector =
> +		((struct seq_file *)file->private_data)->private;
> +	struct intel_connector *intel_connector = to_intel_connector(connector);
> +	struct intel_hdcp *hdcp = &intel_connector->hdcp;
> +
> +	if (!hdcp->shim)
> +		return -EINVAL;
> +
> +	if (len == 0)
> +		return 0;
> +
> +	ret = kstrtouint_from_user(ubuf, len, 0, &hdcp_ver);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (hdcp_ver > HDCP_VERSION_MASK)
> +		return -EINVAL;
> +
> +	hdcp->debugfs_ver_request = hdcp_ver;
A lockless assignment, this would probably not scale.
Could u please add some comment here for current IGT need this is ok,
but for any concurrent usgaes proper locking is required.
Thanks,
Anshuman
> +
> +	*offp += len;
> +
> +	return len;
> +}
> +
> +static const struct file_operations i915_hdcp_ver_request_fops = {
> +	.owner = THIS_MODULE,
> +	.open = i915_hdcp_ver_request_open,
> +	.read = seq_read,
> +	.llseek = seq_lseek,
> +	.release = single_release,
> +	.write = i915_hdcp_ver_request_write
> +};
> +
>  /**
>   * intel_connector_debugfs_add - add i915 specific connector debugfs files
>   * @connector: pointer to a registered drm_connector
> @@ -2215,6 +2281,8 @@ int intel_connector_debugfs_add(struct drm_connector *connector)
>  	    connector->connector_type == DRM_MODE_CONNECTOR_HDMIB) {
>  		debugfs_create_file("i915_hdcp_sink_capability", S_IRUGO, root,
>  				    connector, &i915_hdcp_sink_capability_fops);
> +		debugfs_create_file("i915_hdcp_version_request", 0444, root,
> +				    connector, &i915_hdcp_ver_request_fops);
>  	}
>  
>  	if (INTEL_GEN(dev_priv) >= 10 &&
> -- 
> 2.17.1
> 
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