Re: [PATCH v2 2/2] drm/xe: Mutual exclusivity between CCS-mode and PF

["Kumar G, Naresh" <naresh.kumar.g@intel.com>]

Hi Michal,

please find inlined comments.

On 30-01-2026 03:11, Michal Wajdeczko wrote:
> 
> 
> On 1/29/2026 6:22 PM, Nareshkumar Gollakoti wrote:
>> Due to SLA agreement between PF and VFs,the alternate CCS-mode
>                                            ^
> nit: missing space

Noted

> 
>> cannot be changed when VFs are already enabled.
>> Similarly, enabling VFs is not permitted when the alternate
>> CCS-mode is active.
> 
> maybe it's worth to mention:
> 
> "Currently we block CCS mode changes if driver is running as PF,
>   even if there are no VFs enabled yet."
> 
> above says "why" but what about "how" ? maybe:
> 
> "Use lockdown mechanism provided by the PF to relax that limitation
>   and still enforce above VFs related requirements."
>

Make sense, Noted.

>>
>> Signed-off-by: Nareshkumar Gollakoti <naresh.kumar.g@intel.com>
>> ---
>>   drivers/gpu/drm/xe/xe_gt_ccs_mode.c | 37 ++++++++++++++++++-----------
>>   drivers/gpu/drm/xe/xe_gt_ccs_mode.h | 12 ++++++++++
>>   2 files changed, 35 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..52285a550f34 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)
>>   {
>> @@ -117,12 +118,6 @@ 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 +134,35 @@ 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;
>> +
>> +	/*
>> +	 * Changing default CCS mode is only allowed when there
>> +	 * are no VFs. Try to lockdown PF to find out.
>> +	 */
>> +	if (xe_gt_ccs_mode_default(gt) && IS_SRIOV_PF(xe)) {
>> +		ret = xe_sriov_pf_lockdown(xe);
>> +		if (ret) {
>> +			xe_gt_dbg(gt, "Can't change CCS Mode: VFs are enabled\n");
>> +			return ret;
>> +		}
>>   	}
>>   
>> -	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);
>> +
>> +	/* We may end PF lockdown once CCS mode is default again */
>> +	if (xe_gt_ccs_mode_default(gt) && IS_SRIOV_PF(xe))
>> +		xe_sriov_pf_end_lockdown(xe);
>>   
>>   	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;
>> +}
> 
> nit: do we need this as public helper ?

Currently this function not needed as public.
will move to .c file as a simple static function.

> 
> maybe it should be defined as simple static function in .c ?
>

Agreed.

Thanks,
Naresh

>> +
>>   #endif
>>   
> 
> but the code change LGTM, so with commit msg improved,
> 
> Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
>