[Intel-wired-lan] [PATCH V2 2/2] platform/x86: intel_pmc: Ignore GBE LTR on Tiger Lake platforms

[Jesse Brandeburg <jesse.brandeburg@intel.com>]

David E. Box 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.

Hi David, thanks for looking into this. A few review comments follow,
and then I'll Ack it.
 
> Signed-off-by: David E. Box <david.e.box@linux.intel.com>
> Reviewed-by: Sasha Neftin <sasha.neftin@intel.com>
> Cc: intel-wired-lan at lists.osuosl.org
> Reviewed-by: Rajneesh Bhardwaj <irenic.rajneesh@gmail.com>
> ---
> Changes in V2:
> 	- Pass the bit position instead of the entire mask to the ltr_ignore
> 	  fuction
> 	- Rename the write_ltr_ignore to send_ltr_ignore to differentiate it
> 	  from the caller, ltr_ignore_write.
> 	- Rename variables for clarity
> 
>  drivers/platform/x86/intel_pmc_core.c | 59 ++++++++++++++++++++-------
>  1 file changed, 44 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/platform/x86/intel_pmc_core.c b/drivers/platform/x86/intel_pmc_core.c
> index ee2f757515b0..8d799cfa0e9f 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_send_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 reg;
> +	int err = 0;
>  
>  	mutex_lock(&pmcdev->lock);
>  
> -	if (val > map->ltr_ignore_max) {
> +	if (value > map->ltr_ignore_max) {
>  		err = -EINVAL;
>  		goto out_unlock;
>  	}
>  
> -	fd = pmc_core_reg_read(pmcdev, map->ltr_ignore_offset);
> -	fd |= (1U << val);
> -	pmc_core_reg_write(pmcdev, map->ltr_ignore_offset, fd);
> +	reg = pmc_core_reg_read(pmcdev, map->ltr_ignore_offset);
> +	reg |= (1U << value);

This should just be BIT(value).

> +	pmc_core_reg_write(pmcdev, map->ltr_ignore_offset, reg);
>  
>  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, value;
> +	int err;
> +
> +	buf_size = count < 64 ? count : 64;

isn't this just an open coded buf_size = min_t(u32, count, 64); ?

> +
> +	err = kstrtou32_from_user(userbuf, buf_size, 10, &value);
> +	if (err)
> +		return err;

Why is there no range check or checking on &value?


> +
> +	err = pmc_core_send_ltr_ignore(value);
> +
>  	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 value)
> +{
> +	int err;
> +
> +	err = pmc_core_send_ltr_ignore(value);
> +
> +	return err;

return pmc_core_send_ltr_ignore(value); ?

> +}
> +
>  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(3);
> +	}
> +
>  	pmc_core_dbgfs_register(pmcdev);
>  
>  	device_initialized = true;