RE: [PATCH] platform/x86: intel_pmc: Ignore GBE LTR on Tiger Lake platforms

[Limonciello, Mario]

> -----Original Message-----
> From: Rajneesh Bhardwaj <irenic.rajneesh@xxxxxxxxx>
> Sent: Monday, March 8, 2021 11:32
> To: Limonciello, Mario
> Cc: David E. Box; hdegoede@xxxxxxxxxx; mgross@xxxxxxxxxxxxxxx;
> sasha.neftin@xxxxxxxxx; platform-driver-x86@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; intel-wired-lan@xxxxxxxxxxxxxxxx
> Subject: Re: [PATCH] platform/x86: intel_pmc: Ignore GBE LTR on Tiger Lake
> platforms
> 
> 
> [EXTERNAL EMAIL]
> 
> On Mon, Mar 8, 2021 at 12:20 PM Limonciello, Mario
> <Mario.Limonciello@xxxxxxxx> wrote:
> >
> > >
> > > [EXTERNAL EMAIL]
> > >
> > > Due to a HW limitation, the Latency Tolerance Reporting (LTR) value
> > > programmed in the Tiger Lake GBE controller is not large enough to allow
> > > the platform to enter Package C10, which in turn prevents the platform
> from
> > > achieving its low power target during suspend-to-idle.  Ignore the GBE LTR
> > > value on Tiger Lake. LTR ignore functionality is currently performed
> solely
> > > by a debugfs write call. Split out the LTR code into its own function that
> > > can be called by both the debugfs writer and by this work around.
> > >
> > > Signed-off-by: David E. Box <david.e.box@xxxxxxxxxxxxxxx>
> > > Reviewed-by: Sasha Neftin <sasha.neftin@xxxxxxxxx>
> > > Cc: intel-wired-lan@xxxxxxxxxxxxxxxx
> > > ---
> > >  drivers/platform/x86/intel_pmc_core.c | 55 ++++++++++++++++++++-------
> > >  1 file changed, 42 insertions(+), 13 deletions(-)
> >
> > I feel like this driver change causes a weak reference between e1000e and
> intel_pmc_core.
> > It would mean significantly different behavior if you use e1000e but don't
> have PMC module
> > available for any reason.
> 
> Can you elaborate what would change significantly? This is a FW/HW
> issue and the driver is just doing a work around to let the platform
> enter a deep idle state beyond PC10. If the system could enter PC10
> and was denied entry by PMC only because of a bad LAN LTR, then that's
> purely an e1000e driver/GBE fw issue.
> 
Because the workaround is in pmc driver, the platform behavior becomes tied
to whether this driver was enabled.  Before this the driver was mostly for debugging
purpose and really not necessary.  Now it has a functional purpose.

As such I think it should be made apparent that you need it now for some systems.

> >
> > In this case does it maybe make sense to at least use "imply" in the Kconfig
> for e1000e so
> > that selecting e1000e gets intel-pmc-core enabled too?
> 
> This change would tell PMC to ignore GBE LTR, regardless of which GBE
> driver is selected. This doesn't bind e1000e.

Yeah, that's a good point.

Maybe my suggestion can be to take this into documentation somewhere instead.

> 
> >
> > >
> > > diff --git a/drivers/platform/x86/intel_pmc_core.c
> > > b/drivers/platform/x86/intel_pmc_core.c
> > > index ee2f757515b0..ab31eb646a1a 100644
> > > --- a/drivers/platform/x86/intel_pmc_core.c
> > > +++ b/drivers/platform/x86/intel_pmc_core.c
> > > @@ -863,34 +863,45 @@ static int pmc_core_pll_show(struct seq_file *s,
> void
> > > *unused)
> > >  }
> > >  DEFINE_SHOW_ATTRIBUTE(pmc_core_pll);
> > >
> > > -static ssize_t pmc_core_ltr_ignore_write(struct file *file,
> > > -                                      const char __user *userbuf,
> > > -                                      size_t count, loff_t *ppos)
> > > +static int pmc_core_write_ltr_ignore(u32 value)
> > >  {
> > >       struct pmc_dev *pmcdev = &pmc;
> > >       const struct pmc_reg_map *map = pmcdev->map;
> > > -     u32 val, buf_size, fd;
> > > -     int err;
> > > -
> > > -     buf_size = count < 64 ? count : 64;
> > > -
> > > -     err = kstrtou32_from_user(userbuf, buf_size, 10, &val);
> > > -     if (err)
> > > -             return err;
> > > +     u32 fd;
> > > +     int err = 0;
> > >
> > >       mutex_lock(&pmcdev->lock);
> > >
> > > -     if (val > map->ltr_ignore_max) {
> > > +     if (fls(value) > map->ltr_ignore_max) {
> > >               err = -EINVAL;
> > >               goto out_unlock;
> > >       }
> > >
> > >       fd = pmc_core_reg_read(pmcdev, map->ltr_ignore_offset);
> > > -     fd |= (1U << val);
> > > +     fd |= value;
> > >       pmc_core_reg_write(pmcdev, map->ltr_ignore_offset, fd);
> > >
> > >  out_unlock:
> > >       mutex_unlock(&pmcdev->lock);
> > > +
> > > +     return err;
> > > +}
> > > +
> > > +static ssize_t pmc_core_ltr_ignore_write(struct file *file,
> > > +                                      const char __user *userbuf,
> > > +                                      size_t count, loff_t *ppos)
> > > +{
> > > +     u32 buf_size, val;
> > > +     int err;
> > > +
> > > +     buf_size = count < 64 ? count : 64;
> > > +
> > > +     err = kstrtou32_from_user(userbuf, buf_size, 10, &val);
> > > +     if (err)
> > > +             return err;
> > > +
> > > +     err = pmc_core_write_ltr_ignore(1U << val);
> > > +
> > >       return err == 0 ? count : err;
> > >  }
> > >
> > > @@ -1189,6 +1200,15 @@ static int quirk_xtal_ignore(const struct
> dmi_system_id
> > > *id)
> > >       return 0;
> > >  }
> > >
> > > +static int quirk_ltr_ignore(u32 val)
> > > +{
> > > +     int err;
> > > +
> > > +     err = pmc_core_write_ltr_ignore(val);
> > > +
> > > +     return err;
> > > +}
> > > +
> > >  static const struct dmi_system_id pmc_core_dmi_table[]  = {
> > >       {
> > >       .callback = quirk_xtal_ignore,
> > > @@ -1244,6 +1264,15 @@ static int pmc_core_probe(struct platform_device
> *pdev)
> > >       pmcdev->pmc_xram_read_bit = pmc_core_check_read_lock_bit();
> > >       dmi_check_system(pmc_core_dmi_table);
> > >
> > > +     /*
> > > +      * On TGL, due to a hardware limitation, the GBE LTR blocks PC10
> when
> > > +      * a cable is attached. Tell the PMC to ignore it.
> > > +      */
> > > +     if (pmcdev->map == &tgl_reg_map) {
> > > +             dev_dbg(&pdev->dev, "ignoring GBE LTR\n");
> > > +             quirk_ltr_ignore(1U << 3);
> > > +     }
> > > +
> > >       pmc_core_dbgfs_register(pmcdev);
> > >
> > >       device_initialized = true;
> > > --
> > > 2.25.1
> >
> 
> 
> --
> Thanks,
> Rajneesh