1 files changed, 67 insertions, 0 deletions
diff --git a/drivers/gpu/nova-core/fb.rs b/drivers/gpu/nova-core/fb.rs
new file mode 100644
index 000000000000..bfe3ed063572
--- /dev/null
+++ b/drivers/gpu/nova-core/fb.rs
@@ -0,0 +1,67 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use kernel::prelude::*;
+use kernel::types::ARef;
+use kernel::{dev_warn, device};
+
+use crate::dma::DmaObject;
+use crate::driver::Bar0;
+use crate::gpu::Chipset;
+
+mod hal;
+
+/// Type holding the sysmem flush memory page, a page of memory to be written into the
+/// `NV_PFB_NISO_FLUSH_SYSMEM_ADDR*` registers and used to maintain memory coherency.
+///
+/// Users are responsible for manually calling [`Self::unregister`] before dropping this object,
+/// otherwise the GPU might still use it even after it has been freed.
+pub(crate) struct SysmemFlush {
+    /// Chipset we are operating on.
+    chipset: Chipset,
+    device: ARef<device::Device>,
+    /// Keep the page alive as long as we need it.
+    page: DmaObject,
+}
+
+impl SysmemFlush {
+    /// Allocate a memory page and register it as the sysmem flush page.
+    pub(crate) fn register(
+        dev: &device::Device<device::Bound>,
+        bar: &Bar0,
+        chipset: Chipset,
+    ) -> Result<Self> {
+        let page = DmaObject::new(dev, kernel::page::PAGE_SIZE)?;
+
+        hal::fb_hal(chipset).write_sysmem_flush_page(bar, page.dma_handle())?;
+
+        Ok(Self {
+            chipset,
+            device: dev.into(),
+            page,
+        })
+    }
+
+    /// Unregister the managed sysmem flush page.
+    ///
+    /// In order to gracefully tear down the GPU, users must make sure to call this method before
+    /// dropping the object.
+    pub(crate) fn unregister(&self, bar: &Bar0) {
+        let hal = hal::fb_hal(self.chipset);
+
+        if hal.read_sysmem_flush_page(bar) == self.page.dma_handle() {
+            let _ = hal.write_sysmem_flush_page(bar, 0).inspect_err(|e| {
+                dev_warn!(
+                    &self.device,
+                    "failed to unregister sysmem flush page: {:?}",
+                    e
+                )
+            });
+        } else {
+            // Another page has been registered after us for some reason - warn as this is a bug.
+            dev_warn!(
+                &self.device,
+                "attempt to unregister a sysmem flush page that is not active\n"
+            );
+        }
+    }
+}