Re: [PATCH 01/14] drm/i915/display: Modify debugfs for joiner to force n pipes

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Sep 06, 2024 at 06:27:54PM +0530, Ankit Nautiyal wrote:
> At the moment, the debugfs for joiner allows only to force enable/disable
> pipe joiner for 2 pipes. Modify it to force join 'n' number of pipes,
> where n is a valid pipe joiner configuration.
> This will help in case of ultra joiner where 4 pipes are joined.
> 
> v2:
> -Fix commit message to state that only valid joiner config can be
> forced. (Suraj)
> -Rename the identifiers to have INTEL_BIG/NONE_JOINER_PIPES. (Suraj)
> 
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> ---
>  .../drm/i915/display/intel_display_debugfs.c  | 71 ++++++++++++++++++-
>  .../drm/i915/display/intel_display_types.h    |  8 ++-
>  drivers/gpu/drm/i915/display/intel_dp.c       |  2 +-
>  3 files changed, 77 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_display_debugfs.c b/drivers/gpu/drm/i915/display/intel_display_debugfs.c
> index 830b9eb60976..0ef573afd8a1 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_debugfs.c
> +++ b/drivers/gpu/drm/i915/display/intel_display_debugfs.c
> @@ -1504,6 +1504,73 @@ static int intel_crtc_pipe_show(struct seq_file *m, void *unused)
>  }
>  DEFINE_SHOW_ATTRIBUTE(intel_crtc_pipe);
>  
> +static int i915_joiner_show(struct seq_file *m, void *data)
> +{
> +	struct intel_connector *connector = m->private;
> +	struct drm_i915_private *i915 = to_i915(connector->base.dev);
> +	int ret;
> +
> +	ret = drm_modeset_lock_single_interruptible(&i915->drm.mode_config.connection_mutex);
> +	if (ret)
> +		return ret;

What does that lock do for us?

> +
> +	seq_printf(m, "Force_joined_pipes: %d\n", connector->force_joined_pipes);

This should just be thae bare number. Adding other junk in there just
complicates matters if anyone has to parse this.

> +
> +	drm_modeset_unlock(&i915->drm.mode_config.connection_mutex);
> +
> +	return ret;
> +}
> +
> +static ssize_t i915_joiner_write(struct file *file,
> +				 const char __user *ubuf,
> +				 size_t len, loff_t *offp)
> +{
> +	struct seq_file *m = file->private_data;
> +	struct intel_connector *connector = m->private;
> +	struct drm_i915_private *i915 = to_i915(connector->base.dev);
> +	int force_join_pipes = 0;
> +	int ret;
> +
> +	if (len == 0)
> +		return 0;
> +
> +	drm_dbg(&i915->drm,
> +		"Copied %zu bytes from user to force joiner\n", len);

Leftover debug junk.

> +
> +	ret = kstrtoint_from_user(ubuf, len, 0, &force_join_pipes);
> +	if (ret < 0)
> +		return ret;
> +
> +	drm_dbg(&i915->drm, "Got %d for force joining pipes\n", force_join_pipes);

More.

> +
> +	if (force_join_pipes < INTEL_NONE_JOINER_PIPES ||
> +	    force_join_pipes >= INTEL_INVALID_JOINER_PIPES) {
> +		drm_dbg(&i915->drm, "Ignoring Invalid num of pipes %d for force joining\n",
> +			force_join_pipes);
> +		connector->force_joined_pipes = INTEL_NONE_JOINER_PIPES;
> +	} else {
> +		connector->force_joined_pipes = force_join_pipes;
> +	}

I think just something like
switch (num_pipes) {
case 0: /* or should 1 be the default? */
case 2:
case 4:
	break;
default:
	bad;
}

should do for validation.

> +
> +	*offp += len;

I don't suppose there's any kind of helper for creating a debugfs
file with a standard type, with some kind of caller specified
validation function? Would avoid having to hand roll all this
read syscall cruft for what is a fairly common usecase...

> +
> +	return len;
> +}
> +
> +static int i915_joiner_open(struct inode *inode, struct file *file)
> +{
> +	return single_open(file, i915_joiner_show, inode->i_private);
> +}
> +
> +static const struct file_operations i915_joiner_fops = {
> +	.owner = THIS_MODULE,
> +	.open = i915_joiner_open,
> +	.read = seq_read,
> +	.llseek = seq_lseek,
> +	.release = single_release,
> +	.write = i915_joiner_write
> +};
> +
>  /**
>   * intel_connector_debugfs_add - add i915 specific connector debugfs files
>   * @connector: pointer to a registered intel_connector
> @@ -1553,8 +1620,8 @@ void intel_connector_debugfs_add(struct intel_connector *connector)
>  	if (DISPLAY_VER(i915) >= 11 &&
>  	    (connector_type == DRM_MODE_CONNECTOR_DisplayPort ||
>  	     connector_type == DRM_MODE_CONNECTOR_eDP)) {
> -		debugfs_create_bool("i915_bigjoiner_force_enable", 0644, root,
> -				    &connector->force_bigjoiner_enable);
> +		debugfs_create_file("i915_joiner_force_enable", 0644, root,
> +				    connector, &i915_joiner_fops);
>  	}
>  
>  	if (connector_type == DRM_MODE_CONNECTOR_DSI ||
> diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
> index 733de5edcfdb..c213fb61ceb7 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> @@ -486,6 +486,12 @@ struct intel_hdcp {
>  	enum transcoder stream_transcoder;
>  };
>  
> +enum intel_joiner_pipe_count {
> +	INTEL_NONE_JOINER_PIPES = 0,
> +	INTEL_BIG_JOINER_PIPES = 2,
> +	INTEL_INVALID_JOINER_PIPES,
> +};

That just looks like obfuscation to me.
Just a bare number should do.

> +
>  struct intel_connector {
>  	struct drm_connector base;
>  	/*
> @@ -524,7 +530,7 @@ struct intel_connector {
>  
>  	struct intel_dp *mst_port;
>  
> -	bool force_bigjoiner_enable;
> +	enum intel_joiner_pipe_count force_joined_pipes;
>  
>  	struct {
>  		struct drm_dp_aux *dsc_decompression_aux;
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index a1fcedfd404b..862a460c32b7 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -1271,7 +1271,7 @@ bool intel_dp_need_joiner(struct intel_dp *intel_dp,
>  		return false;
>  
>  	return clock > i915->display.cdclk.max_dotclk_freq || hdisplay > 5120 ||
> -	       connector->force_bigjoiner_enable;
> +	       connector->force_joined_pipes == INTEL_BIG_JOINER_PIPES;
>  }
>  
>  bool intel_dp_has_dsc(const struct intel_connector *connector)
> -- 
> 2.45.2

-- 
Ville Syrjälä
Intel