[PATCH] drm/xe/pf: Keep VF LMEM BAR size low if no VFs enabled

[Marcin Bernatowicz <marcin.bernatowicz@linux.intel.com>]

When VFs are enabled on dGFX the driver resizes the PF VF_LMEM_BAR to
fit the requested layout. After VFs are disabled the PF VF BAR
size is left as-is. On platforms with tight MMIO apertures a
subsequent unplug/rescan followed by another enable may fail with:

  "VF BAR …: can't assign; no space"

because the PCI core reserves address space based on the (now large) VF
template, often multiplied by totalvfs.

v2: Use pci.total_vfs in helper (Michał Wajdeczko)

Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/5937
Fixes: 94eae6ee4c2d ("drm/xe/pf: Set VF LMEM BAR size")
Signed-off-by: Marcin Bernatowicz <marcin.bernatowicz@linux.intel.com>
Cc: Michał Wajdeczko <michal.wajdeczko@intel.com>
Cc: Michał Winiarski <michal.winiarski@intel.com>
---
 drivers/gpu/drm/xe/xe_pci_sriov.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_pci_sriov.c b/drivers/gpu/drm/xe/xe_pci_sriov.c
index af05db07162e..ff003a650f79 100644
--- a/drivers/gpu/drm/xe/xe_pci_sriov.c
+++ b/drivers/gpu/drm/xe/xe_pci_sriov.c
@@ -144,11 +144,26 @@ static int resize_vf_vram_bar(struct xe_device *xe, int num_vfs)
 	return pci_iov_vf_bar_set_size(pdev, VF_LMEM_BAR, __fls(sizes));
 }
 
+static void reduce_vf_vram_bar_size(struct xe_device *xe)
+{
+	struct pci_dev *pdev = to_pci_dev(xe->drm.dev);
+	int err;
+
+	if (!IS_DGFX(xe))
+		return;
+
+	err = resize_vf_vram_bar(xe, pci_sriov_get_totalvfs(pdev));
+	if (err)
+		xe_sriov_info(xe, "Failed to reduce VF LMEM BAR size: %d\n",
+			      err);
+}
+
 static int pf_enable_vfs(struct xe_device *xe, int num_vfs)
 {
 	struct pci_dev *pdev = to_pci_dev(xe->drm.dev);
 	int total_vfs = xe_sriov_pf_get_totalvfs(xe);
 	int err;
+	bool vf_vram_bar_resized = false;
 
 	xe_assert(xe, IS_SRIOV_PF(xe));
 	xe_assert(xe, num_vfs > 0);
@@ -178,6 +193,8 @@ static int pf_enable_vfs(struct xe_device *xe, int num_vfs)
 		err = resize_vf_vram_bar(xe, num_vfs);
 		if (err)
 			xe_sriov_info(xe, "Failed to set VF LMEM BAR size: %d\n", err);
+		else
+			vf_vram_bar_resized = true;
 	}
 
 	err = pci_enable_sriov(pdev, num_vfs);
@@ -194,6 +211,9 @@ static int pf_enable_vfs(struct xe_device *xe, int num_vfs)
 	return num_vfs;
 
 failed:
+	if (vf_vram_bar_resized)
+		reduce_vf_vram_bar_size(xe);
+
 	pf_unprovision_vfs(xe, num_vfs);
 	xe_pm_runtime_put(xe);
 out:
@@ -218,6 +238,8 @@ static int pf_disable_vfs(struct xe_device *xe)
 
 	pci_disable_sriov(pdev);
 
+	reduce_vf_vram_bar_size(xe);
+
 	pf_reset_vfs(xe, num_vfs);
 
 	pf_unprovision_vfs(xe, num_vfs);
-- 
2.31.1