drm/i915/gt: Add helper for shmem copy to iosys_map

Add a variant of shmem_read() that takes a iosys_map pointer rather
than a plain pointer as argument. It's mostly a copy __shmem_rw() but
adapting the api and removing the write support since there's currently
only need to use iosys_map as destination.

Reworking __shmem_rw() to share the implementation was tempting, but
finding a good balance between reuse and clarity pushed towards a little
code duplication. Since the function is small, just add the similar
function with a copy/paste/adapt approach.

v2: Add an offset as argument and instead of using a map iterator, use the
offset to keep track of where we are writing data to.

Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Atwood <matthew.s.atwood@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220216174147.3073235-4-lucas.demarchi@intel.com

drivers/gpu/drm/i915/gt/shmem_utils.c

@@ -3,6 +3,7 @@
  * Copyright © 2020 Intel Corporation
  */
 
+#include <linux/iosys-map.h>
 #include <linux/mm.h>
 #include <linux/pagemap.h>
 #include <linux/shmem_fs.h>
@@ -123,6 +124,37 @@ static int __shmem_rw(struct file *file, loff_t off,
 	return 0;
 }
 
+int shmem_read_to_iosys_map(struct file *file, loff_t off,
+			    struct iosys_map *map, size_t map_off, size_t len)
+{
+	unsigned long pfn;
+
+	for (pfn = off >> PAGE_SHIFT; len; pfn++) {
+		unsigned int this =
+			min_t(size_t, PAGE_SIZE - offset_in_page(off), len);
+		struct page *page;
+		void *vaddr;
+
+		page = shmem_read_mapping_page_gfp(file->f_mapping, pfn,
+						   GFP_KERNEL);
+		if (IS_ERR(page))
+			return PTR_ERR(page);
+
+		vaddr = kmap(page);
+		iosys_map_memcpy_to(map, map_off, vaddr + offset_in_page(off),
+				    this);
+		mark_page_accessed(page);
+		kunmap(page);
+		put_page(page);
+
+		len -= this;
+		map_off += this;
+		off = 0;
+	}
+
+	return 0;
+}
+
 int shmem_read(struct file *file, loff_t off, void *dst, size_t len)
 {
 	return __shmem_rw(file, off, dst, len, false);

drivers/gpu/drm/i915/gt/shmem_utils.h

@@ -8,6 +8,7 @@
 
 #include <linux/types.h>
 
+struct iosys_map;
 struct drm_i915_gem_object;
 struct file;
 
@@ -17,6 +18,8 @@ struct file *shmem_create_from_object(struct drm_i915_gem_object *obj);
 void *shmem_pin_map(struct file *file);
 void shmem_unpin_map(struct file *file, void *ptr);
 
+int shmem_read_to_iosys_map(struct file *file, loff_t off,
+			    struct iosys_map *map, size_t map_off, size_t len);
 int shmem_read(struct file *file, loff_t off, void *dst, size_t len);
 int shmem_write(struct file *file, loff_t off, void *src, size_t len);