Re: [PATCH] drm/xe/: Mutual Exclusivity b/w Multi CCS Mode & SRIOV VF Provisioning

[Michal Wajdeczko <michal.wajdeczko@intel.com>]

On 9/29/2025 10:36 AM, Nareshkumar Gollakoti wrote:
> Due to SLA agreement between PF and VFs, multi CCS mode can't
> be enabled when VFs are already enabled.
> Similarly, enabling VFs is disabled when multi ccs mode enabled.

s/ccs/CCS
> 
> v2:function xe_device_is_vf_enabled has been refactored to
> xe_sriov_pf_has_vfs_enabled and moved to xe_sriov_pf_helper.h.
> The code now distinctly checks for SR-IOV VF mode and
> SR-IOV PF with VFs enabled.
> Log messages have been updated to explicitly state the current mode.
> The function xe_multi_ccs_mode_enabled is moved to xe_device.h
> 
> v3: Described missed arg documentation for xe_sriov_pf_has_vfs_enabled

you can keep version log under ---

> 
> Signed-off-by: Nareshkumar Gollakoti <naresh.kumar.g@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_device.h           |  8 ++++++++
>  drivers/gpu/drm/xe/xe_gt_ccs_mode.c      | 14 +++++++++++---
>  drivers/gpu/drm/xe/xe_pci_sriov.c        |  6 ++++++
>  drivers/gpu/drm/xe/xe_sriov_pf_helpers.h | 13 +++++++++++++
>  4 files changed, 38 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_device.h b/drivers/gpu/drm/xe/xe_device.h
> index 32cc6323b7f6..986f9cabb897 100644
> --- a/drivers/gpu/drm/xe/xe_device.h
> +++ b/drivers/gpu/drm/xe/xe_device.h
> @@ -172,6 +172,14 @@ static inline bool xe_device_has_lmtt(struct xe_device *xe)
>  	return IS_DGFX(xe);
>  }
>  
> +static inline bool xe_multi_ccs_mode_enabled(struct xe_device *xe)
> +{
> +	/* Multi CCS mode supported exclusively on GT0 */
> +	struct xe_gt *gt = xe_device_get_gt(xe, 0);

beware of the discussion at https://patchwork.freedesktop.org/series/155114/#rev1

> +
> +	return gt->ccs_mode > 1;
> +}
> +
>  u32 xe_device_ccs_bytes(struct xe_device *xe, u64 size);
>  
>  void xe_device_snapshot_print(struct xe_device *xe, struct drm_printer *p);
> diff --git a/drivers/gpu/drm/xe/xe_gt_ccs_mode.c b/drivers/gpu/drm/xe/xe_gt_ccs_mode.c
> index 50fffc9ebf62..584f3245fc7d 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_helpers.h"
>  
>  static void __xe_gt_apply_ccs_mode(struct xe_gt *gt, u32 num_engines)
>  {
> @@ -117,9 +118,16 @@ 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)));
> +	/*
> +	 * Check if the device is:
> +	 * 1. Operating as an SR-IOV Virtual Function (VF), or
> +	 * 2. An SR-IOV Physical Function (PF) with one or more VFs enabled.
> +	 * Enabling multi CCS mode is not permitted in either scenario.

in case 1 it is rather "not possible", so I would split that case, as suggested in [1]

[1] https://patchwork.freedesktop.org/patch/674760/?series=154538&rev=1#comment_1240131

> +	 */
> +	if (IS_SRIOV_VF(xe) || xe_sriov_pf_has_vfs_enabled(xe)) {
> +		const char *mode_str = !strcmp(xe_sriov_mode_to_string(xe_device_sriov_mode(xe)),

hmm, what's the goal of comparing mode string, where you already have access to the mode? 

but, what's the point of exposing "gt_ccs_mode_attrs" for VFs when they can't do anything with them?

maybe you can get rid of one condition above, by simply checking for IS_VF when adding sysfs attributes?

> +					"SR-IOV VF") ? "SR-IOV VF" : "SR-IOV PF with VFs Enabled";
> +		xe_gt_dbg(gt, "Can't change compute mode when running as %s\n", mode_str);
>  		return -EOPNOTSUPP;
>  	}
>  
> diff --git a/drivers/gpu/drm/xe/xe_pci_sriov.c b/drivers/gpu/drm/xe/xe_pci_sriov.c
> index af05db07162e..71c1d998ba82 100644
> --- a/drivers/gpu/drm/xe/xe_pci_sriov.c
> +++ b/drivers/gpu/drm/xe/xe_pci_sriov.c
> @@ -155,6 +155,12 @@ static int pf_enable_vfs(struct xe_device *xe, int num_vfs)
>  	xe_assert(xe, num_vfs <= total_vfs);
>  	xe_sriov_dbg(xe, "enabling %u VF%s\n", num_vfs, str_plural(num_vfs));
>  
> +	if (xe_multi_ccs_mode_enabled(xe)) {
> +		xe_sriov_info(xe, "Disable multi-ccs mode before enabling VF's\n");

multi-CCS ?

> +
> +		return -ECANCELED;
> +	}
> +

I still don't see how do you want to protect against the case when CCS mode will be
changed right after above check but before PF actually enable VFs
>  	err = xe_sriov_pf_wait_ready(xe);
>  	if (err)
>  		goto out;
> diff --git a/drivers/gpu/drm/xe/xe_sriov_pf_helpers.h b/drivers/gpu/drm/xe/xe_sriov_pf_helpers.h
> index dd1df950b021..e26837091375 100644
> --- a/drivers/gpu/drm/xe/xe_sriov_pf_helpers.h
> +++ b/drivers/gpu/drm/xe/xe_sriov_pf_helpers.h
> @@ -43,4 +43,17 @@ static inline struct mutex *xe_sriov_pf_master_mutex(struct xe_device *xe)
>  	return &xe->sriov.pf.master_lock;
>  }
>  
> +/**
> + * xe_sriov_pf_has_vfs_enabled() - Determines if the PF has any VFs enabled
> + * @xe: ptr to xe_device
> + *
> + * Return: true if one or more VFs are enabled on the PF, false otherwise.
> + */
> +static inline bool xe_sriov_pf_has_vfs_enabled(const struct xe_device *xe)
> +{
> +	struct pci_dev *pdev = to_pci_dev(xe->drm.dev);
> +
> +	return pci_num_vf(pdev) > 0;
> +}
> +
>  #endif