Re: [PATCH v4] platform/x86/intel/pmc: core: Add support to show LTR-ignored components

["Box, David E" <david.e.box@xxxxxxxxx>]

Hi Rajat,

On Sun, 2023-02-05 at 23:14 +0530, Rajat Khandelwal wrote:
> Currently, 'ltr_ignore' sysfs attribute, when read, returns nothing, even
> if there are components whose LTR values have been ignored.
> 
> This patch adds the feature to print out such components, if they exist.
> 
> Signed-off-by: Rajat Khandelwal <rajat.khandelwal@xxxxxxxxxxxxxxx>
> ---
> 
> v4: Mutex unlock during error conditions
> 
> v3: Incorporated a mutex lock for accessing 'ltr_ignore_list'
> 
> v2: kmalloc -> devm_kmalloc
> 
>  drivers/platform/x86/intel/pmc/core.c | 59 ++++++++++++++++++++++-----
>  drivers/platform/x86/intel/pmc/core.h |  2 +-
>  2 files changed, 49 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/platform/x86/intel/pmc/core.c
> b/drivers/platform/x86/intel/pmc/core.c
> index 3a15d32d7644..f9d4b2865b03 100644
> --- a/drivers/platform/x86/intel/pmc/core.c
> +++ b/drivers/platform/x86/intel/pmc/core.c
> @@ -53,6 +53,17 @@ const struct pmc_bit_map msr_map[] = {
>         {}
>  };
>  
> +/* Mutual exclusion to access the list of LTR-ignored components */
> +static DEFINE_MUTEX(ltr_entry_mutex);
> +
> +struct ltr_entry {
> +       u32 comp_index;
> +       const char *comp_name;
> +       struct list_head node;
> +};
> +
> +static LIST_HEAD(ltr_ignore_list);
> +
>  static inline u32 pmc_core_reg_read(struct pmc_dev *pmcdev, int reg_offset)
>  {
>         return readl(pmcdev->regbase + reg_offset);
> @@ -435,27 +446,18 @@ static int pmc_core_pll_show(struct seq_file *s, void
> *unused)
>  }
>  DEFINE_SHOW_ATTRIBUTE(pmc_core_pll);
>  
> -int pmc_core_send_ltr_ignore(struct pmc_dev *pmcdev, u32 value)
> +void pmc_core_send_ltr_ignore(struct pmc_dev *pmcdev, u32 value)
>  {
>         const struct pmc_reg_map *map = pmcdev->map;
>         u32 reg;
> -       int err = 0;
>  
>         mutex_lock(&pmcdev->lock);
>  
> -       if (value > map->ltr_ignore_max) {
> -               err = -EINVAL;
> -               goto out_unlock;
> -       }
> -
>         reg = pmc_core_reg_read(pmcdev, map->ltr_ignore_offset);
>         reg |= 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,
> @@ -464,6 +466,8 @@ static ssize_t pmc_core_ltr_ignore_write(struct file
> *file,
>  {
>         struct seq_file *s = file->private_data;
>         struct pmc_dev *pmcdev = s->private;
> +       const struct pmc_reg_map *map = pmcdev->map;
> +       struct ltr_entry *entry;
>         u32 buf_size, value;
>         int err;
>  
> @@ -473,13 +477,46 @@ static ssize_t pmc_core_ltr_ignore_write(struct file
> *file,
>         if (err)
>                 return err;
>  
> -       err = pmc_core_send_ltr_ignore(pmcdev, value);
> +       if (value > map->ltr_ignore_max)
> +               return -EINVAL;
> +
> +       mutex_lock(&ltr_entry_mutex);
> +
> +       list_for_each_entry(entry, &ltr_ignore_list, node) {
> +               if (entry->comp_index == value) {
> +                       err = -EEXIST;

Do we need to return an error here? We don't offer a way to undo the ignore and
rewriting it doesn't hurt anything. I'm okay with ignoring this.

> +                       goto out_unlock;
> +               }
> +       }
> +
> +       entry = devm_kmalloc(&pmcdev->pdev->dev, sizeof(*entry), GFP_KERNEL);
> +       if (!entry) {
> +               err = -ENOMEM;
> +               goto out_unlock;
> +       }
> +
> +       entry->comp_name = map->ltr_show_sts[value].name;
> +       entry->comp_index = value;
> +       list_add_tail(&entry->node, &ltr_ignore_list);
> +
> +       pmc_core_send_ltr_ignore(pmcdev, value);
> +
> +out_unlock:
> +       mutex_unlock(&ltr_entry_mutex);

You can allocate your entry and do the assignment before you take the list lock.
If the allocation fails, return immediately without a goto.

You can also move pmc_core_send_ltr_ignore() after the unlock.

David

>  
>         return err == 0 ? count : err;
>  }
>  
>  static int pmc_core_ltr_ignore_show(struct seq_file *s, void *unused)
>  {
> +       struct ltr_entry *entry;
> +
> +       mutex_lock(&ltr_entry_mutex);
> +       list_for_each_entry(entry, &ltr_ignore_list, node) {
> +               seq_printf(s, "%s\n", entry->comp_name);
> +       }
> +       mutex_unlock(&ltr_entry_mutex);
> +
>         return 0;
>  }
>  
> diff --git a/drivers/platform/x86/intel/pmc/core.h
> b/drivers/platform/x86/intel/pmc/core.h
> index 810204d758ab..da35b0fcbe6e 100644
> --- a/drivers/platform/x86/intel/pmc/core.h
> +++ b/drivers/platform/x86/intel/pmc/core.h
> @@ -396,7 +396,7 @@ extern const struct pmc_reg_map adl_reg_map;
>  extern const struct pmc_reg_map mtl_reg_map;
>  
>  extern void pmc_core_get_tgl_lpm_reqs(struct platform_device *pdev);
> -extern int pmc_core_send_ltr_ignore(struct pmc_dev *pmcdev, u32 value);
> +extern void pmc_core_send_ltr_ignore(struct pmc_dev *pmcdev, u32 value);
>  
>  void spt_core_init(struct pmc_dev *pmcdev);
>  void cnp_core_init(struct pmc_dev *pmcdev);
> -- 
> 2.34.1
>