Re: [PATCH 01/19] drm/i915/lnl+/tc: Fix handling of an enabled/disconnected dp-alt sink

[Luca Coelho <luca@coelho.fi>]

On Thu, 2025-08-07 at 15:50 +0300, Imre Deak wrote:
> On Thu, Aug 07, 2025 at 03:33:04PM +0300, Imre Deak wrote:
> > On Thu, Aug 07, 2025 at 03:19:17PM +0300, Jani Nikula wrote:
> > > On Thu, 07 Aug 2025, Imre Deak <imre.deak@intel.com> wrote:
> > > > On Thu, Aug 07, 2025 at 01:59:21PM +0300, Luca Coelho wrote:
> > > > > On Tue, 2025-08-05 at 10:36 +0300, Imre Deak wrote:
> > > > > > The TypeC PHY HW readout during driver loading and system resume
> > > > > > determines which TypeC mode the PHY is in (legacy/DP-alt/TBT-alt) and
> > > > > > whether the PHY is connected, based on the PHY's Owned and Ready flags.
> > > > > > For the PHY to be in DP-alt or legacy mode and for the PHY to be in the
> > > > > > connected state in these modes, both the Owned (set by the BIOS/driver)
> > > > > > and the Ready (set by the HW) flags should be set.
> > > > > > 
> > > > > > On ICL-MTL the HW kept the PHY's Ready flag set after the driver
> > > > > > connected the PHY by acquiring the PHY ownership (by setting the Owned
> > > > > > flag), until the driver disconnected the PHY by releasing the PHY
> > > > > > ownership (by clearing the Owned flag). On LNL+ this has changed, in
> > > > > > that the HW clears the Ready flag as soon as the sink gets disconnected,
> > > > > > even if the PHY ownership was acquired already and hence the PHY is
> > > > > > being used by the display.
> > > > > > 
> > > > > > When inheriting the HW state from BIOS for a PHY connected in DP-alt
> > > > > > mode on which the sink got disconnected - i.e. in a case where the sink
> > > > > > was connected while BIOS/GOP was running and so the sink got enabled
> > > > > > connecting the PHY, but the user disconnected the sink by the time the
> > > > > > driver loaded - the PHY Owned but not Ready state must be accounted for
> > > > > > on LNL+ according to the above. Do that by assuming on LNL+ that the PHY
> > > > > > is connected in DP-alt mode whenever the PHY Owned flag is set,
> > > > > > regardless of the PHY Ready flag.
> > > > > > 
> > > > > > This fixes a problem on LNL+, where the PHY TypeC mode / connected state
> > > > > > was detected incorrectly for a DP-alt sink, which got connected and then
> > > > > > disconnected by the user in the above way.
> > > > > > 
> > > > > > Cc: stable@vger.kernel.org # v6.8+
> > > > > > Reported-by: Charlton Lin <charlton.lin@intel.com>
> > > > > > Tested-by: Khaled Almahallawy <khaled.almahallawy@intel.com>
> > > > > > Signed-off-by: Imre Deak <imre.deak@intel.com>
> > > > > > ---
> > > > > >  drivers/gpu/drm/i915/display/intel_tc.c | 16 ++++++++++------
> > > > > >  1 file changed, 10 insertions(+), 6 deletions(-)
> > > > > > 
> > > > > > diff --git a/drivers/gpu/drm/i915/display/intel_tc.c b/drivers/gpu/drm/i915/display/intel_tc.c
> > > > > > index 3bc57579fe53e..73a08bd84a70a 100644
> > > > > > --- a/drivers/gpu/drm/i915/display/intel_tc.c
> > > > > > +++ b/drivers/gpu/drm/i915/display/intel_tc.c
> > > > > > @@ -1226,14 +1226,18 @@ static void tc_phy_get_hw_state(struct intel_tc_port *tc)
> > > > > >  	tc->phy_ops->get_hw_state(tc);
> > > > > >  }
> > > > > >  
> > > > > > -static bool tc_phy_is_ready_and_owned(struct intel_tc_port *tc,
> > > > > > -				      bool phy_is_ready, bool phy_is_owned)
> > > > > > +static bool tc_phy_in_legacy_or_dp_alt_mode(struct intel_tc_port *tc,
> > > > > > +					    bool phy_is_ready, bool phy_is_owned)
> > > > > 
> > > > > Personally I don't like the "or" in the function name.  You're
> > > > > returning a boolean which is true or false.  The return value is akin
> > > > > to answering "Yes/No" to the question "Is it black or white".
> > > > 
> > > > The question the function is meant to answer is "Is the PHY in legacy or
> > > > DP-alt mode?". The return value is true (yes) if the PHY is in either
> > > > legacy or DP-alt mode, false (no) if the PHY is neither in legacy or
> > > > DP-alt mode. There are many other uses of "or" in function names in this
> > > > sense, so not sure how else I'd name this one. Simply leaving out "or"
> > > > would make it less clear that the legacy and DP-alt modes are two
> > > > separate modes.

Right, I missed that.  But one shouldn't have to go read the function
implementation to know what it's doing.


> > > 
> > > What's the opposite of "Is the PHY in legacy or DP-alt mode"?
> > > 
> > > Would that lead to a simpler name, with the reversed return value?
> > 
> > The opposite is either TBT-alt or disconnected mode, so the reversal
> > would result in the same function name format.
> 
> Would you be ok with
> 
> tc_phy_owned_by_display()
> 
> ?

This sounds much better! And it's indeed what you're looking for.  It
doesn't matter if it's legacy DP-alt, TBT-alt or whatever.  What you're
checking is actually whether display owns the PHY.  So this is a much
better choice IMHO. :)

--
Cheers,
Luca.