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

[Rajneesh Bhardwaj]

Hi David

Overall, it looks like the right thing to do but i have a few
comments. See below.

On Fri, Mar 5, 2021 at 2:07 PM David E. Box <david.e.box@xxxxxxxxxxxxxxx> wrote:
>
> 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.
>

I presume this must be the last resort to use such quirk and you've
already considered a user space tuning program or fw patch is not an
option on this generation of SOCs.

> 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(-)
>
> 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)

This sounds a bit confusing with pmc_core_ltr_ignore_write.

>  {
>         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;

lets just call it value

> +       int err = 0;
>
>         mutex_lock(&pmcdev->lock);
>
> -       if (val > map->ltr_ignore_max) {
> +       if (fls(value) > map->ltr_ignore_max) {

I am not sure why you're considering a bit position here. We rather
use absolute value for this and we already preserve (OR) previously
programmed LTR while changing to the new desired value.  Current
modification would allow users to supply even bigger values than the
MAX IP ignore allowed. This can be useful when you want to ignore more
than 1 IP at a time but that's not how we usually use it for debug.
This is more for a user space debug script to deal with.
https://01.org/blogs/rajneesh/2019/using-power-management-controller-drivers-debug-low-power-platform-states

>                 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);

Can this be made a part of *_reg_map itself if intended to be used for
more future platforms? Otherwise we just leave it as a one time quirk.

> +       }
> +
>         pmc_core_dbgfs_register(pmcdev);
>
>         device_initialized = true;
> --
> 2.25.1
>


-- 
Thanks,
Rajneesh