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

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

On Mon, Sep 09, 2024 at 11:10:16AM +0530, Nautiyal, Ankit K wrote:
> 
> On 9/6/2024 8:24 PM, Ville Syrjälä wrote:
> > On Fri, Sep 06, 2024 at 05:46:11PM +0300, Ville Syrjälä wrote:
> >> 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? */
> > I suppose both 0 and 1 should be accepted. 0==not forced, 1==forced to
> > exactly one pipe (ie. no joiner despite what the automagic logic
> > is saying).
> 
> I understand 0 as not forced. I didnt get the meaning of forcing to one 
> pipe.
> 
> Does this mean, disable joiner? (Perhaps do not use joiner even for the 
> cases where driver thinks joiner is required)
> 
> How should we handle the case in driver, where it is 1?

Whatever code that determines how many pipes will should:
1) if the override is non-zero just use it
2) otherwise determine the number by using whatever
   logic is appropriate

> 
> 
> Regards,
> 
> Ankit
> 
> >
> >> case 2:
> >> case 4:
> >> 	break;
> >> default:
> >> 	bad;
> >> }
> >>
> >> should do for validation.
> >>

-- 
Ville Syrjälä
Intel