Re: [PATCH 7/8] drm/i915/dsc: Add debugfs entry to validate DSC fractional bpp

["Sharma, Swati2" <swati2.sharma@intel.com>]

On 21-Sep-23 5:44 PM, Jani Nikula wrote:
> On Thu, 21 Sep 2023, "Sharma, Swati2" <swati2.sharma@intel.com> wrote:
>> On 21-Sep-23 1:30 PM, Jani Nikula wrote:
>>> On Wed, 13 Sep 2023, Mitul Golani <mitulkumar.ajitkumar.golani@intel.com> wrote:
>>>> From: Swati Sharma <swati2.sharma@intel.com>
>>>>
>>>> DSC_Sink_BPP_Precision entry is added to i915_dsc_fec_support_show
>>>> to depict sink's precision.
>>>> Also, new debugfs entry is created to enforce fractional bpp.
>>>> If Force_DSC_Fractional_BPP_en is set then while iterating over
>>>> output bpp with fractional step size we will continue if output_bpp is
>>>> computed as integer. With this approach, we will be able to validate
>>>> DSC with fractional bpp.
>>>>
>>>> v2:
>>>> Add drm_modeset_unlock to new line(Suraj)
>>>>
>>>> Signed-off-by: Swati Sharma <swati2.sharma@intel.com>
>>>> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
>>>> Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.golani@intel.com>
>>>> Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
>>>> ---
>>>>    .../drm/i915/display/intel_display_debugfs.c  | 83 +++++++++++++++++++
>>>>    .../drm/i915/display/intel_display_types.h    |  1 +
>>>>    2 files changed, 84 insertions(+)
>>>>
>>>> diff --git a/drivers/gpu/drm/i915/display/intel_display_debugfs.c b/drivers/gpu/drm/i915/display/intel_display_debugfs.c
>>>> index f05b52381a83..776ab96def1f 100644
>>>> --- a/drivers/gpu/drm/i915/display/intel_display_debugfs.c
>>>> +++ b/drivers/gpu/drm/i915/display/intel_display_debugfs.c
>>>> @@ -1244,6 +1244,8 @@ static int i915_dsc_fec_support_show(struct seq_file *m, void *data)
>>>>    								      DP_DSC_YCbCr420_Native)),
>>>>    			   str_yes_no(drm_dp_dsc_sink_supports_format(intel_dp->dsc_dpcd,
>>>>    								      DP_DSC_YCbCr444)));
>>>> +		seq_printf(m, "DSC_Sink_BPP_Precision: %d\n",
>>>> +			   drm_dp_dsc_sink_bpp_incr(intel_dp->dsc_dpcd));
>>>>    		seq_printf(m, "Force_DSC_Enable: %s\n",
>>>>    			   str_yes_no(intel_dp->force_dsc_en));
>>>>    		if (!intel_dp_is_edp(intel_dp))
>>>> @@ -1436,6 +1438,84 @@ static const struct file_operations i915_dsc_output_format_fops = {
>>>>    	.write = i915_dsc_output_format_write
>>>>    };
>>>>    
>>>> +static int i915_dsc_fractional_bpp_show(struct seq_file *m, void *data)
>>>> +{
>>>> +	struct drm_connector *connector = m->private;
>>>> +	struct drm_device *dev = connector->dev;
>>>> +	struct drm_crtc *crtc;
>>>> +	struct intel_dp *intel_dp;
>>>> +	struct intel_encoder *encoder = intel_attached_encoder(to_intel_connector(connector));
>>>> +	int ret;
>>>> +
>>>> +	if (!encoder)
>>>> +		return -ENODEV;
>>>> +
>>>> +	ret = drm_modeset_lock_single_interruptible(&dev->mode_config.connection_mutex);
>>>> +	if (ret)
>>>> +		return ret;
>>>> +
>>>> +	crtc = connector->state->crtc;
>>>> +	if (connector->status != connector_status_connected || !crtc) {
>>>> +		ret = -ENODEV;
>>>> +		goto out;
>>>> +	}
>>>> +
>>>> +	intel_dp = intel_attached_dp(to_intel_connector(connector));
>>>> +	seq_printf(m, "Force_DSC_Fractional_BPP_Enable: %s\n",
>>>> +		   str_yes_no(intel_dp->force_dsc_fractional_bpp_en));
>>>
>>> Why "Force_DSC_Fractional_BPP_Enable" in the output?
>>>
>>> Usually debugfs files, like sysfs files, for stuff like this should be
>>> attributes, one thing per file. Why print a long name for it, if the
>>> name of the debugfs file is the name of the attribute?
>>>
>>> And even if you print it for humans, why the underscores?
>>
>> Hi Jani,
>> Followed same strategy as we are doing for other dsc scenarios like
>> force_dsc.
>> Even naming convention followed same as other dsc stuff like
>> Force_DSC_Enable, etc.
>> All DSC related enteries have underscores in its naming convention.
> 
> There's value in that, though maybe my comment highlights I'm not fond
> of the existing stuff. ;)

Sure, I can work on cleanup part later.

> 
>> May be i can consolidate other dsc debugfs enteries into
>> one as a cleanup task later. But it will impact IGT aswell. And i'm not
>> sure if we can break compatibility but since IGT (intel as only vendor)
>> is the only consumer, may be we change at both places and clean it up.
> 
> We can do what we want with debugfs, as long as we change both the
> driver and igt.

Sure, will make corresponding changes in both IGT and KMD.

> 
>>
>>>
>>>> +
>>>> +out:
>>>> +	drm_modeset_unlock(&dev->mode_config.connection_mutex);
>>>> +
>>>> +	return ret;
>>>> +}
>>>> +
>>>> +static ssize_t i915_dsc_fractional_bpp_write(struct file *file,
>>>> +					     const char __user *ubuf,
>>>> +					     size_t len, loff_t *offp)
>>>> +{
>>>> +	struct drm_connector *connector =
>>>> +		((struct seq_file *)file->private_data)->private;
>>>
>>> I know this is copy-pasted from elsewhere, but really it's nicer to
>>> avoid the cast, and copy-paste from the places that get this right:
>>>
>>> 	struct seq_file *m = file->private_data;
>>>           struct drm_connector *connector = m->private;
>>
>> Done.
>>
>>>
>>>> +	struct intel_encoder *encoder = intel_attached_encoder(to_intel_connector(connector));
>>>> +	struct drm_i915_private *i915 = to_i915(encoder->base.dev);
>>>> +	struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
>>>> +	bool dsc_fractional_bpp_enable = false;
>>>> +	int ret;
>>>> +
>>>> +	if (len == 0)
>>>> +		return 0;
>>>
>>> kstrtobool_from_user() has this covered.
>>
>> Done.
>>
>>>
>>>> +
>>>> +	drm_dbg(&i915->drm,
>>>> +		"Copied %zu bytes from user to force fractional bpp for DSC\n", len);
>>>
>>> That's useless.
>>
>> Done.
>>
>>>
>>>> +
>>>> +	ret = kstrtobool_from_user(ubuf, len, &dsc_fractional_bpp_enable);
>>>> +	if (ret < 0)
>>>> +		return ret;
>>>> +
>>>> +	drm_dbg(&i915->drm, "Got %s for DSC Fractional BPP Enable\n",
>>>> +		(dsc_fractional_bpp_enable) ? "true" : "false");
>>>
>>> Is this useful?
>>
>> Yes, to know when fractional bpp is enabled.
> 
> I think it would be more useful to debug log this at the use site, not
> when you're setting the debugfs knob.

We already have those in IGT. Like said, to maintain consitency with 
other dsc func() like fec_support_write(), this debug print is added 
here. I can drop and will drop from fec_support_write() too during cleanup.

> 
> BR,
> Jani.
> 
> 
> 
> 
>>
>>>
>>>> +	intel_dp->force_dsc_fractional_bpp_en = dsc_fractional_bpp_enable;
>>>> +
>>>> +	*offp += len;
>>>> +
>>>> +	return len;
>>>> +}
>>>> +
>>>> +static int i915_dsc_fractional_bpp_open(struct inode *inode,
>>>> +					struct file *file)
>>>> +{
>>>> +	return single_open(file, i915_dsc_fractional_bpp_show, inode->i_private);
>>>> +}
>>>> +
>>>> +static const struct file_operations i915_dsc_fractional_bpp_fops = {
>>>> +	.owner = THIS_MODULE,
>>>> +	.open = i915_dsc_fractional_bpp_open,
>>>> +	.read = seq_read,
>>>> +	.llseek = seq_lseek,
>>>> +	.release = single_release,
>>>> +	.write = i915_dsc_fractional_bpp_write
>>>> +};
>>>> +
>>>>    /*
>>>>     * Returns the Current CRTC's bpc.
>>>>     * Example usage: cat /sys/kernel/debug/dri/0/crtc-0/i915_current_bpc
>>>> @@ -1513,6 +1593,9 @@ void intel_connector_debugfs_add(struct intel_connector *intel_connector)
>>>>    
>>>>    		debugfs_create_file("i915_dsc_output_format", 0644, root,
>>>>    				    connector, &i915_dsc_output_format_fops);
>>>> +
>>>> +		debugfs_create_file("i915_dsc_fractional_bpp", 0644, root,
>>>> +				    connector, &i915_dsc_fractional_bpp_fops);
>>>>    	}
>>>>    
>>>>    	if (connector->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 69bcabec4a29..27b31cb4c7b4 100644
>>>> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
>>>> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
>>>> @@ -1797,6 +1797,7 @@ struct intel_dp {
>>>>    	/* Display stream compression testing */
>>>>    	bool force_dsc_en;
>>>>    	int force_dsc_output_format;
>>>> +	bool force_dsc_fractional_bpp_en;
>>>>    	int force_dsc_bpc;
>>>>    
>>>>    	bool hobl_failed;
>>>
> 

With above KMD changes IGT is already rb'ed and validated
https://patchwork.freedesktop.org/series/117493/#rev12
I request if we can get ack on this. As cleanup task,
will make changes as requested.