Re: [PATCH v1 2/2] drm/xe: Mutual exclusivity between CCS-mode and PF

["K V P, Satyanarayana" <satyanarayana.k.v.p@intel.com>]

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On 28-Nov-25 10:48 PM, Nareshkumar Gollakoti wrote:
> Due to SLA agreement between PF and VFs,the alternate CCS-mode
> cannot be changed when VFs are already enabled.
> Similarly, enabling VFs is not permitted when the alternate
> CCS-mode is active.
>
> Signed-off-by: Nareshkumar Gollakoti<naresh.kumar.g@intel.com>
> ---
>   drivers/gpu/drm/xe/xe_gt_ccs_mode.c | 59 ++++++++++++++++++++++-------
>   drivers/gpu/drm/xe/xe_gt_ccs_mode.h | 12 ++++++
>   2 files changed, 57 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/gpu/drm/xe/xe_gt_ccs_mode.c b/drivers/gpu/drm/xe/xe_gt_ccs_mode.c
> index e146e00b0ca2..6652c468e1be 100644
> --- a/drivers/gpu/drm/xe/xe_gt_ccs_mode.c
> +++ b/drivers/gpu/drm/xe/xe_gt_ccs_mode.c
> @@ -13,6 +13,7 @@
>   #include "xe_gt_sysfs.h"
>   #include "xe_mmio.h"
>   #include "xe_sriov.h"
> +#include "xe_sriov_pf.h"
>   
>   static void __xe_gt_apply_ccs_mode(struct xe_gt *gt, u32 num_engines)
>   {
> @@ -108,6 +109,36 @@ ccs_mode_show(struct device *kdev,
>   	return sysfs_emit(buf, "%u\n", gt->ccs_mode);
>   }
>   
> +static int gt_prepare_ccs_mode_enabling(struct xe_gt *gt)
> +{
> +	struct xe_device *xe = gt_to_xe(gt);
> +
> +	if (!IS_SRIOV_PF(xe))
> +		return 0;

The ccs mode will not be enabled for native mode (non-virtualized mode) 
with this. It should be something like

if (IS_SRIOV_VF(xe))

         return 0;

Same comment for other places as well.

> +
> +	/*
> +	 * We can't change CCS-mode when VFs are already enabled
> +	 * and we must prevent enabling VFs when alternate
> +	 * CCS-mode is active
> +	 */
> +	if (xe_gt_ccs_mode_default(gt))
> +		return xe_sriov_pf_lockdown(xe);
> +
> +	return 0;
> +}
> +
> +static void gt_finish_ccs_mode_enabling(struct xe_gt *gt)
> +{
> +	struct xe_device *xe = gt_to_xe(gt);
> +
> +	if (!IS_SRIOV_PF(xe))
> +		return;
> +
> +	/* Allow enabling VFs, if CCS-mode changed to default mode */
> +	if (xe_gt_ccs_mode_default(gt))
> +		xe_sriov_pf_end_lockdown(xe);
> +}
> +
>   static ssize_t
>   ccs_mode_store(struct device *kdev, struct device_attribute *attr,
>   	       const char *buff, size_t count)
> @@ -117,12 +148,6 @@ ccs_mode_store(struct device *kdev, struct device_attribute *attr,
>   	u32 num_engines, num_slices;
>   	int ret;
>   
> -	if (IS_SRIOV(xe)) {
> -		xe_gt_dbg(gt, "Can't change compute mode when running as %s\n",
> -			  xe_sriov_mode_to_string(xe_device_sriov_mode(xe)));
> -		return -EOPNOTSUPP;
> -	}
> -
>   	ret = kstrtou32(buff, 0, &num_engines);
>   	if (ret)
>   		return ret;
> @@ -139,21 +164,27 @@ ccs_mode_store(struct device *kdev, struct device_attribute *attr,
>   	}
>   
>   	/* CCS mode can only be updated when there are no drm clients */
> -	mutex_lock(&xe->drm.filelist_mutex);
> +	guard(mutex)(&xe->drm.filelist_mutex);
>   	if (!list_empty(&xe->drm.filelist)) {
> -		mutex_unlock(&xe->drm.filelist_mutex);
>   		xe_gt_dbg(gt, "Rejecting compute mode change as there are active drm clients\n");
>   		return -EBUSY;
>   	}
>   
> -	if (gt->ccs_mode != num_engines) {
> -		xe_gt_info(gt, "Setting compute mode to %d\n", num_engines);
> -		gt->ccs_mode = num_engines;
> -		xe_gt_record_user_engines(gt);
> -		xe_gt_reset(gt);
> +	if (gt->ccs_mode == num_engines)
> +		return count;
> +
> +	ret = gt_prepare_ccs_mode_enabling(gt);
> +	if (ret) {
> +		xe_gt_dbg(gt, "Rejecting compute mode change as VFs are enabled\n");
> +		return ret;
>   	}

The function gt_prepare_ccs_mode_enabling() never returning non-zero 
error if VFs are enabled.

>   
> -	mutex_unlock(&xe->drm.filelist_mutex);
> +	xe_gt_info(gt, "Setting compute mode to %d\n", num_engines);
> +	gt->ccs_mode = num_engines;
> +	xe_gt_record_user_engines(gt);
> +	xe_gt_reset(gt);
> +

Do we need to apply gt reset after changing CCS mode? If yes, add a 
comment with why do we need it.

-Satya.

> +	gt_finish_ccs_mode_enabling(gt);
>   
>   	return count;
>   }
> diff --git a/drivers/gpu/drm/xe/xe_gt_ccs_mode.h b/drivers/gpu/drm/xe/xe_gt_ccs_mode.h
> index f8779852cf0d..53a595b0882c 100644
> --- a/drivers/gpu/drm/xe/xe_gt_ccs_mode.h
> +++ b/drivers/gpu/drm/xe/xe_gt_ccs_mode.h
> @@ -20,5 +20,17 @@ static inline bool xe_gt_ccs_mode_enabled(const struct xe_gt *gt)
>   	return hweight32(CCS_MASK(gt)) > 1;
>   }
>   
> +/**
> + * xe_gt_ccs_mode_default() - Check if CCS mode is default (single CCS mode)
> + * @gt: GT structure
> + *
> + * Return: %true if actual CCS mode is single mode, or
> + *         %false otherwise (CCS in alternate/multi mode)
> + */
> +static inline bool xe_gt_ccs_mode_default(struct xe_gt *gt)
> +{
> +	return gt->ccs_mode == 1;
> +}
> +
>   #endif
>   

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