Commit 3078d9c8 authored Jul 02, 2024 by Michal Wajdeczko

drm/xe: Use VF_CAP_REG for device wmb



To force a write barrier on the device memory, we write to the
SOFTWARE_FLAGS_SPR33 register, but this particular register was
selected because it was one of the writable and unused register.

Since a write barrier should also work if we use the read-only
register, switch to VF_CAP_REG register that is also marked as
accessible for VFs.

While at it, add simple kernel-doc for xe_device_wmb() function.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240702183704.1022-4-michal.wajdeczko@intel.com

parent 466a6c38

drivers/gpu/drm/xe/xe_device.c

+10 −1

Original line number	Diff line number	Diff line
		@@ -744,13 +744,22 @@ void xe_device_shutdown(struct xe_device *xe)
		{
		}

		/**
		* xe_device_wmb() - Device specific write memory barrier
		* @xe: the &xe_device
		*
		* While wmb() is sufficient for a barrier if we use system memory, on discrete
		* platforms with device memory we additionally need to issue a register write.
		* Since it doesn't matter which register we write to, use the read-only VF_CAP
		* register that is also marked as accessible by the VFs.
		*/
		void xe_device_wmb(struct xe_device *xe)
		{
		struct xe_gt *gt = xe_root_mmio_gt(xe);

		wmb();
		if (IS_DGFX(xe))
		xe_mmio_write32(gt, SOFTWARE_FLAGS_SPR33, 0);
		xe_mmio_write32(gt, VF_CAP_REG, 0);
		}

		/**