[Intel-gfx] [PATCH] drm/i915/ttm: implement access_memory

[Matthew Auld]

It looks like we need this for local-memory, if we want to use ptrace.
Something more is still needed if we want to handle non-mappable memory,
which looks quite annoying.

References: https://gitlab.freedesktop.org/drm/intel/-/issues/6989
Signed-off-by: Matthew Auld <matthew.auld at intel.com>
Cc: Nirmoy Das <nirmoy.das at intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 43 +++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
index 3dc6acfcf4ec..4f533e0c92b4 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
@@ -699,6 +699,48 @@ static unsigned long i915_ttm_io_mem_pfn(struct ttm_buffer_object *bo,
 	return ((base + sg_dma_address(sg)) >> PAGE_SHIFT) + ofs;
 }
 
+static int i915_ttm_access_memory(struct ttm_buffer_object *bo,
+				  unsigned long offset, void *buf,
+				  int len, int write)
+{
+	unsigned long page = offset >> PAGE_SHIFT;
+	unsigned long bytes_left = len;
+	int ret;
+
+	/*
+	 * TODO: For now just let it fail if the resource is non-mappable,
+	 * otherwise we need to perform the memcpy from the gpu here, without
+	 * interfering with the object (like moving the entire thing).
+	 */
+
+	offset -= page << PAGE_SHIFT;
+	do {
+		unsigned long bytes = min(bytes_left, PAGE_SIZE - offset);
+		struct ttm_bo_kmap_obj map;
+		void __iomem *ptr;
+		bool is_iomem;
+
+		ret = ttm_bo_kmap(bo, page, 1, &map);
+		if (ret)
+			return ret;
+
+		ptr = ttm_kmap_obj_virtual(&map, &is_iomem) + offset;
+		WARN_ON_ONCE(!is_iomem);
+		if (write)
+			memcpy_toio(ptr, buf, bytes);
+		else
+			memcpy_fromio(buf, ptr, bytes);
+		ttm_bo_kunmap(&map);
+
+		page++;
+		buf += bytes;
+		bytes_left -= bytes;
+		offset = 0;
+	} while (bytes_left);
+
+	return len;
+}
+
 /*
  * All callbacks need to take care not to downcast a struct ttm_buffer_object
  * without checking its subclass, since it might be a TTM ghost object.
@@ -715,6 +757,7 @@ static struct ttm_device_funcs i915_ttm_bo_driver = {
 	.delete_mem_notify = i915_ttm_delete_mem_notify,
 	.io_mem_reserve = i915_ttm_io_mem_reserve,
 	.io_mem_pfn = i915_ttm_io_mem_pfn,
+	.access_memory = i915_ttm_access_memory,
 };
 
 /**
-- 
2.37.3