Re: [PATCH V4 16/17] platform/x86/intel/pmc: Add debug attribute for Die C6 counter

[Ilpo Järvinen]

On Wed, 18 Oct 2023, David E. Box wrote:

> Add a "die_c6_us_show" debugfs attribute.  Reads the counter value using
> Intel Platform Monitoring Technology (PMT) driver API. This counter is
> useful for determining the idle residency of CPUs in the compute tile.
> 
> Signed-off-by: David E. Box <david.e.box@xxxxxxxxxxxxxxx>
> ---
> V4 - no change
> 
> V3 - Split previous PATCH V2 13. Separates implementation (this patch) from
>      platform specific use (next patch)
> 
> V2 - Remove use of __func__
>    - Use HZ_PER_MHZ
>    - Fix missing newlines in printks
> 
>  drivers/platform/x86/intel/pmc/core.c | 55 +++++++++++++++++++++++++++
>  drivers/platform/x86/intel/pmc/core.h |  4 ++
>  2 files changed, 59 insertions(+)
> 
> diff --git a/drivers/platform/x86/intel/pmc/core.c b/drivers/platform/x86/intel/pmc/core.c
> index fcb0dc702aea..02f3e909cf22 100644
> --- a/drivers/platform/x86/intel/pmc/core.c
> +++ b/drivers/platform/x86/intel/pmc/core.c
> @@ -20,6 +20,7 @@
>  #include <linux/pci.h>
>  #include <linux/slab.h>
>  #include <linux/suspend.h>
> +#include <linux/units.h>
>  
>  #include <asm/cpu_device_id.h>
>  #include <asm/intel-family.h>
> @@ -27,6 +28,7 @@
>  #include <asm/tsc.h>
>  
>  #include "core.h"
> +#include "../pmt/telemetry.h"
>  
>  /* Maximum number of modes supported by platfoms that has low power mode capability */
>  const char *pmc_lpm_modes[] = {
> @@ -822,6 +824,47 @@ static int pmc_core_substate_req_regs_show(struct seq_file *s, void *unused)
>  }
>  DEFINE_SHOW_ATTRIBUTE(pmc_core_substate_req_regs);
>  
> +static unsigned int pmc_core_get_crystal_freq(void)
> +{
> +	unsigned int eax_denominator, ebx_numerator, ecx_hz, edx;
> +
> +	if (boot_cpu_data.cpuid_level < 0x15)
> +		return 0;
> +
> +	eax_denominator = ebx_numerator = ecx_hz = edx = 0;
> +
> +	/* CPUID 15H TSC/Crystal ratio, plus optionally Crystal Hz */
> +	cpuid(0x15, &eax_denominator, &ebx_numerator, &ecx_hz, &edx);
> +
> +	if (ebx_numerator == 0 || eax_denominator == 0)
> +		return 0;
> +
> +	return ecx_hz;
> +}
> +
> +static int pmc_core_die_c6_us_show(struct seq_file *s, void *unused)
> +{
> +	struct pmc_dev *pmcdev = s->private;
> +	u64 die_c6_res, count;
> +	int ret;
> +
> +	if (!pmcdev->crystal_freq) {
> +		dev_warn_once(&pmcdev->pdev->dev, "Bad crystal frequency\n");

Isn't it more like crystal frequency is not provided rather than bad 
frequency?

> +		return -EINVAL;

-EINVAL is not good value to return here since there was nothing wrong 
with the input. Maybe -ENXIO would be better.

> +	}
> +
> +	ret = pmt_telem_read(pmcdev->punit_ep, pmcdev->die_c6_offset,
> +			     &count, 1);
> +	if (ret)
> +		return ret;
> +
> +	die_c6_res = div64_u64(count * HZ_PER_MHZ, pmcdev->crystal_freq);
> +	seq_printf(s, "%llu\n", die_c6_res);
> +
> +	return 0;
> +}
> +DEFINE_SHOW_ATTRIBUTE(pmc_core_die_c6_us);
> +
>  static int pmc_core_lpm_latch_mode_show(struct seq_file *s, void *unused)
>  {
>  	struct pmc_dev *pmcdev = s->private;
> @@ -1118,6 +1161,12 @@ static void pmc_core_dbgfs_register(struct pmc_dev *pmcdev)
>  				    pmcdev->dbgfs_dir, pmcdev,
>  				    &pmc_core_substate_req_regs_fops);
>  	}
> +
> +	if (pmcdev->has_die_c6) {
> +		debugfs_create_file("die_c6_us_show", 0444,
> +				    pmcdev->dbgfs_dir, pmcdev,
> +				    &pmc_core_die_c6_us_fops);
> +	}
>  }
>  
>  static const struct x86_cpu_id intel_pmc_core_ids[] = {
> @@ -1212,6 +1261,10 @@ static void pmc_core_clean_structure(struct platform_device *pdev)
>  		pci_dev_put(pmcdev->ssram_pcidev);
>  		pci_disable_device(pmcdev->ssram_pcidev);
>  	}
> +
> +	if (pmcdev->punit_ep)
> +		pmt_telem_unregister_endpoint(pmcdev->punit_ep);
> +
>  	platform_set_drvdata(pdev, NULL);
>  	mutex_destroy(&pmcdev->lock);
>  }
> @@ -1232,6 +1285,8 @@ static int pmc_core_probe(struct platform_device *pdev)
>  	if (!pmcdev)
>  		return -ENOMEM;
>  
> +	pmcdev->crystal_freq = pmc_core_get_crystal_freq();
> +
>  	platform_set_drvdata(pdev, pmcdev);
>  	pmcdev->pdev = pdev;
>  
> diff --git a/drivers/platform/x86/intel/pmc/core.h b/drivers/platform/x86/intel/pmc/core.h
> index 85b6f6ae4995..6d7673145f90 100644
> --- a/drivers/platform/x86/intel/pmc/core.h
> +++ b/drivers/platform/x86/intel/pmc/core.h
> @@ -16,6 +16,8 @@
>  #include <linux/bits.h>
>  #include <linux/platform_device.h>
>  
> +struct telem_endpoint;
> +

This seems unrelated to the patch.

-- 
 i.

>  #define SLP_S0_RES_COUNTER_MASK			GENMASK(31, 0)
>  
>  #define PMC_BASE_ADDR_DEFAULT			0xFE000000
> @@ -357,6 +359,7 @@ struct pmc {
>   * @devs:		pointer to an array of pmc pointers
>   * @pdev:		pointer to platform_device struct
>   * @ssram_pcidev:	pointer to pci device struct for the PMC SSRAM
> + * @crystal_freq:	crystal frequency from cpuid
>   * @dbgfs_dir:		path to debugfs interface
>   * @pmc_xram_read_bit:	flag to indicate whether PMC XRAM shadow registers
>   *			used to read MPHY PG and PLL status are available
> @@ -374,6 +377,7 @@ struct pmc_dev {
>  	struct dentry *dbgfs_dir;
>  	struct platform_device *pdev;
>  	struct pci_dev *ssram_pcidev;
> +	unsigned int crystal_freq;
>  	int pmc_xram_read_bit;
>  	struct mutex lock; /* generic mutex lock for PMC Core */
>  
>