Re: [PATCH] drm/i915/dp: Perform 30ms delay after source OUI write

[Lyude Paul]

On Mon, 2021-11-15 at 12:53 +0200, Jani Nikula wrote:
> On Fri, 12 Nov 2021, Lyude Paul <lyude@xxxxxxxxxx> wrote:
> > While working on supporting the Intel HDR backlight interface, I noticed
> > that there's a couple of laptops that will very rarely manage to boot up
> > without detecting Intel HDR backlight support - even though it's supported
> > on the system. One example of such a laptop is the Lenovo P17 1st
> > generation.
> > 
> > Following some investigation Ville Syrjälä did through the docs they have
> > available to them, they discovered that there's actually supposed to be a
> > 30ms wait after writing the source OUI before we begin setting up the rest
> > of the backlight interface.
> > 
> > This seems to be correct, as adding this 30ms delay seems to have
> > completely fixed the probing issues I was previously seeing. So - let's
> > start performing a 30ms wait after writing the OUI, which we do in a
> > manner
> > similar to how we keep track of PPS delays (e.g. record the timestamp of
> > the OUI write, and then wait for however many ms are left since that
> > timestamp right before we interact with the backlight) in order to avoid
> > waiting any longer then we need to. As well, this also avoids us
> > performing
> > this delay on systems where we don't end up using the HDR backlight
> > interface.
> 
> Ugh. Thanks for digging into this.

haha, np! You should thank Ville for finding the hidden docs that told us
about this :).

> 
> The only thing that I dislike with the implementation is splitting the
> implementation to two places. See how well we've managed to shove all of
> the PPS waits inside intel_pps.c. Almost all of intel_dp->pps is managed
> within intel_pps.c.

gotcha, I think I meant to do this after I got things working but forgot
before I sent this out, will respin ASAP

> 
> I think I'd actually add a intel_dp_wait_source_oui() or something in
> intel_dp.c, so all of the details about source OUI and
> intel_dp->last_oui_write access would be localized.
> 
> 
> BR,
> Jani.
> 
> 
> > 
> > Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
> > Fixes: 4a8d79901d5b ("drm/i915/dp: Enable Intel's HDR backlight interface
> > (only SDR for now)")
> > Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> > Cc: <stable@xxxxxxxxxxxxxxx> # v5.12+
> > ---
> >  drivers/gpu/drm/i915/display/intel_display_types.h    |  3 +++
> >  drivers/gpu/drm/i915/display/intel_dp.c               |  3 +++
> >  drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c | 11 +++++++++++
> >  3 files changed, 17 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h
> > b/drivers/gpu/drm/i915/display/intel_display_types.h
> > index ea1e8a6e10b0..b9c967837872 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> > +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> > @@ -1653,6 +1653,9 @@ struct intel_dp {
> >         struct intel_dp_pcon_frl frl;
> >  
> >         struct intel_psr psr;
> > +
> > +       /* When we last wrote the OUI for eDP */
> > +       unsigned long last_oui_write;
> >  };
> >  
> >  enum lspcon_vendor {
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
> > b/drivers/gpu/drm/i915/display/intel_dp.c
> > index 0a424bf69396..77d9a9390c1e 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -29,6 +29,7 @@
> >  #include <linux/i2c.h>
> >  #include <linux/notifier.h>
> >  #include <linux/slab.h>
> > +#include <linux/timekeeping.h>
> >  #include <linux/types.h>
> >  
> >  #include <asm/byteorder.h>
> > @@ -2010,6 +2011,8 @@ intel_edp_init_source_oui(struct intel_dp *intel_dp,
> > bool careful)
> >  
> >         if (drm_dp_dpcd_write(&intel_dp->aux, DP_SOURCE_OUI, oui,
> > sizeof(oui)) < 0)
> >                 drm_err(&i915->drm, "Failed to write source OUI\n");
> > +
> > +       intel_dp->last_oui_write = jiffies;
> >  }
> >  
> >  /* If the device supports it, try to set the power state appropriately */
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > index 569d17b4d00f..2c35b999ec2c 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > @@ -96,6 +96,13 @@
> >  #define INTEL_EDP_BRIGHTNESS_OPTIMIZATION_1                           
> > 0x359
> >  
> >  /* Intel EDP backlight callbacks */
> > +static void
> > +wait_for_oui(struct drm_i915_private *i915, struct intel_dp *intel_dp)
> > +{
> > +       drm_dbg_kms(&i915->drm, "Performing OUI wait\n");
> > +       wait_remaining_ms_from_jiffies(intel_dp->last_oui_write, 30);
> > +}
> > +
> >  static bool
> >  intel_dp_aux_supports_hdr_backlight(struct intel_connector *connector)
> >  {
> > @@ -106,6 +113,8 @@ intel_dp_aux_supports_hdr_backlight(struct
> > intel_connector *connector)
> >         int ret;
> >         u8 tcon_cap[4];
> >  
> > +       wait_for_oui(i915, intel_dp);
> > +
> >         ret = drm_dp_dpcd_read(aux, INTEL_EDP_HDR_TCON_CAP0, tcon_cap,
> > sizeof(tcon_cap));
> >         if (ret != sizeof(tcon_cap))
> >                 return false;
> > @@ -204,6 +213,8 @@ intel_dp_aux_hdr_enable_backlight(const struct
> > intel_crtc_state *crtc_state,
> >         int ret;
> >         u8 old_ctrl, ctrl;
> >  
> > +       wait_for_oui(i915, intel_dp);
> > +
> >         ret = drm_dp_dpcd_readb(&intel_dp->aux,
> > INTEL_EDP_HDR_GETSET_CTRL_PARAMS, &old_ctrl);
> >         if (ret != 1) {
> >                 drm_err(&i915->drm, "Failed to read current backlight
> > control mode: %d\n", ret);
> 

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat