Re: [Intel-gfx] [PATCH] drm/i915/DG{1, 2}: FIXME Temporary hammer to disable rpm

[Andi Shyti <andi.shyti@linux.intel.com>]

Hi Anshuman,

On Wed, Sep 14, 2022 at 10:33:15AM -0400, Rodrigo Vivi wrote:
> On Wed, Sep 14, 2022 at 07:45:53PM +0530, Anshuman Gupta wrote:
> > DG1 and DG2 has lmem, and cpu can access the lmem objects
> > via mmap and i915 internal i915_gem_object_pin_map() for
> > i915 own usages. Both of these methods has pre-requisite
> > requirement to keep GFX PCI endpoint in D0 for a supported
> > iomem transaction over PCI link. (Refer PCIe specs 5.3.1.4.1)
> > 
> > TODO:
> > With respect to i915_gem_object_pin_map(), every caller
> > has to grab a wakeref if gem object lies in lmem.
> > 
> > Till we fix all issues related to runtime PM, we need
> > to keep runtime PM disable on both DG1 and DG2.
> > 
> > Cc: Matthew Auld <matthew.auld@intel.com>
> > Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
> > ---
> >  drivers/gpu/drm/i915/i915_pci.c | 21 +++++++++++++++++++++
> >  1 file changed, 21 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_pci.c b/drivers/gpu/drm/i915/i915_pci.c
> > index 77e7df21f539..f31d7f5399cc 100644
> > --- a/drivers/gpu/drm/i915/i915_pci.c
> > +++ b/drivers/gpu/drm/i915/i915_pci.c
> > @@ -931,6 +931,26 @@ static const struct intel_device_info dg1_info = {
> >  		BIT(VCS0) | BIT(VCS2),
> >  	/* Wa_16011227922 */
> >  	.__runtime.ppgtt_size = 47,
> > +
> > +	/*
> > +	 *  FIXME: Temporary hammer to disable rpm.
> > +	 *  As per PCIe specs 5.3.1.4.1, all iomem read write request over a PCIe
> > +	 *  function will be unsupported in case PCIe endpoint function is in D3.
> > +	 *  But both DG1/DG2 has a hardware bug that violates the PCIe specs

/has/have/

> > +	 *  and supports the iomem read write transaction over PCIe bus despite

/supports/support/

> > +	 *  endpoint is D3 state.
> > +	 *  Due to above H/W bug, we had never observed any issue with i915 runtime
> > +	 *  PM versus lmem access.
> > +	 *  But this issue gets discover when PCIe gfx endpoint's upstream

/gets discover/becomes visible/

> > +	 *  bridge enters to D3, at this point any lmem read/write access will be
> > +	 *  returned as unsupported request. But again this issue is not observed
> > +	 *  on every platform because it has been observed on few host machines
> > +	 *  DG1/DG2 endpoint's upstream bridge does not binds with pcieport driver.

/binds/bind/

> > +	 *  which really disables the PCIe power savings and leaves the bridge to D0
> > +	 *  state.
> > +	 *  Let's disable i915 rpm till we fix all known issue with lmem access in D3.
> > +	 */
> > +	.has_runtime_pm = 0,
> >  };
> >  
> >  static const struct intel_device_info adl_s_info = {
> > @@ -1076,6 +1096,7 @@ static const struct intel_device_info dg2_info = {
> >  	XE_LPD_FEATURES,
> >  	.__runtime.cpu_transcoder_mask = BIT(TRANSCODER_A) | BIT(TRANSCODER_B) |
> >  			       BIT(TRANSCODER_C) | BIT(TRANSCODER_D),
> > +	.has_runtime_pm = 0,
> 
> The FIXME msg can be smaller, but it also needs to be here.

I actually like the comment, is very clear and helps
understanding the issue :)

Thanks again for addressing the issue and with the hope to see
the proper fix soon:

Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>

Thanks,
Andi

> With this in place fell free to use:
> 
> Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> 
> Since the proper solution might take a while let's protect from this case,
> regardless of any other on going discussion about the force_probe protection.
> 
> 
> >  	.require_force_probe = 1,
> >  };
> >  
> > -- 
> > 2.26.2
> >