[PATCH] drm/i915/pcode: Wait 10 seconds for pcode to settle

[Andi Shyti]

On Wed, Jan 11, 2023 at 03:18:38PM +0200, Jani Nikula wrote:
> On Wed, 11 Jan 2023, Andi Shyti <andi.shyti at linux.intel.com> wrote:
> > From: Aravind Iddamsetty <aravind.iddamsetty at intel.com>
> >
> > During module load not all the punit transaction have completed
> > and we might end up timing out, as shown by the following
> > warning:
> 
> Root cause?
> 
> >
> >    i915 0000:4d:00.0: drm_WARN_ON_ONCE(timeout_base_ms > 3)
> >
> > Wait 10 seconds for the punit to settle and complete any
> > outstanding transactions upon module load.
> >
> > Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/7814
> >
> 
> No blank lines between the tag lines please.

I don't consider "Closes:" to be a tag even if someone is using
it as such. AFAIK is not mentioned it in any of the kernel docs
(e.g. Documentation/process/maintainer-tip.rst).

Not to confuse it with a normal tag, I wanted to put it in
parenthesis or rephrase it.

> > Signed-off-by: Aravind Iddamsetty <aravind.iddamsetty at intel.com>
> > Co-developed-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
> > Signed-off-by: Andi Shyti <andi.shyti at linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_pcode.c | 35 ++++++++++++++++++++++++++----
> >  1 file changed, 31 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_pcode.c b/drivers/gpu/drm/i915/intel_pcode.c
> > index a234d9b4ed14..3db2ba439bb5 100644
> > --- a/drivers/gpu/drm/i915/intel_pcode.c
> > +++ b/drivers/gpu/drm/i915/intel_pcode.c
> > @@ -204,15 +204,42 @@ int skl_pcode_request(struct intel_uncore *uncore, u32 mbox, u32 request,
> >  #undef COND
> >  }
> >  
> > +static int pcode_init_wait(struct intel_uncore *uncore, int timeout_ms)
> > +{
> > +	if (__intel_wait_for_register_fw(uncore,
> > +					 GEN6_PCODE_MAILBOX,
> > +					 GEN6_PCODE_READY, 0,
> > +					 500, timeout_ms,
> > +					 NULL))
> > +		return -EPROBE_DEFER;
> 
> This is already done within skl_pcode_request -> skl_pcode_try_request
> -> __snb_pcode_rw path, with waits in skl_pcode_request.

the idea is to check for PCODE_READY even before checking if
data are sent/received by pcode. And this is only during boot
time. While skl_pcode_request is called in other contexts as
well.

In other words here I want to start the communication when I
already know that the punit is ready. Otherwise I would hit an
-EAGAIN and fail.

> Is there anyone who still understands what's being waited for, where,
> for how long, and why in the different code paths? I know I don't, and
> this isn't helping.

I think it depends on hardware. There are some documents roaming
around with some boot time and reset time calculation.

> There's also no explanation on the -EPROBE_DEFER return in the commit
> message or comments or anywhere.

we haven't really failed, right? We just need some time for the
punit to be ready and try to probe again (remember we are here in
module probe).

Thanks for the review,
Andi

> Again, root cause?
> 
> BR,
> Jani.
> 
> 
> > +
> > +	return skl_pcode_request(uncore,
> > +				 DG1_PCODE_STATUS,
> > +				 DG1_UNCORE_GET_INIT_STATUS,
> > +				 DG1_UNCORE_INIT_STATUS_COMPLETE,
> > +				 DG1_UNCORE_INIT_STATUS_COMPLETE, timeout_ms);
> > +}
> > +
> >  int intel_pcode_init(struct intel_uncore *uncore)
> >  {
> > +	int err;
> > +
> >  	if (!IS_DGFX(uncore->i915))
> >  		return 0;
> >  
> > -	return skl_pcode_request(uncore, DG1_PCODE_STATUS,
> > -				 DG1_UNCORE_GET_INIT_STATUS,
> > -				 DG1_UNCORE_INIT_STATUS_COMPLETE,
> > -				 DG1_UNCORE_INIT_STATUS_COMPLETE, 180000);
> > +	/*
> > +	 * Wait 10 seconds so that the punit to settle and complete
> > +	 * any outstanding transactions upon module load
> > +	 */
> > +	err = pcode_init_wait(uncore, 10000);
> > +
> > +	if (err) {
> > +		drm_notice(&uncore->i915->drm,
> > +			   "Waiting for HW initialisation...\n");
> > +		err = pcode_init_wait(uncore, 180000);
> > +	}
> > +
> > +	return err;
> >  }
> >  
> >  int snb_pcode_read_p(struct intel_uncore *uncore, u32 mbcmd, u32 p1, u32 p2, u32 *val)
> 
> -- 
> Jani Nikula, Intel Open Source Graphics Center