On Fri, Feb 04, 2022 at 08:15:12PM +0100, Thomas Zimmermann wrote:
Hi
Am 04.02.22 um 18:44 schrieb Lucas De Marchi:
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.
Cc: Matt Roper <matthew.d.roper@xxxxxxxxx>
Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
Cc: David Airlie <airlied@xxxxxxxx>
Cc: Daniel Vetter <daniel@xxxxxxxx>
Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Signed-off-by: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
---
drivers/gpu/drm/i915/gt/shmem_utils.c | 33 +++++++++++++++++++++++++++
drivers/gpu/drm/i915/gt/shmem_utils.h | 3 +++
2 files changed, 36 insertions(+)
diff --git a/drivers/gpu/drm/i915/gt/shmem_utils.c b/drivers/gpu/drm/i915/gt/shmem_utils.c
index 0683b27a3890..764adefdb4be 100644
--- a/drivers/gpu/drm/i915/gt/shmem_utils.c
+++ b/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 +124,38 @@ static int __shmem_rw(struct file *file, loff_t off,
return 0;
}
Here's a good example of how to avoid iosys_map_incr() and use the
memcpy offset:
+int shmem_read_to_iosys_map(struct file *file, loff_t off,
+ struct iosys_map *map, size_t len)
+{
+ struct iosys_map map_iter = *map;
Rather replace map_iter with something like
unsigned long map_off = 0;
+ 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_iter, 0, vaddr + offset_in_page(off),
+ this);
Use map_off to index into map directly.
+ mark_page_accessed(page);
+ kunmap(page);
+ put_page(page);
+
+ len -= this;
+ iosys_map_incr(&map_iter, this);
Raplace iosys_map_incr() with map_off += this;
+ off = 0;
Maybe off += this ?
Wouldn't that be wrong? AFAICS `off` is the offset of the file (source) and we
zero it here so just the first iteration considers it as a page offset -
next iterations are expected to copy whole pages or the remaining of the
buffer.
Encapsulating the dest offset calculation inside iosys_map with an iter
was a way to avoid this kind of bugs in places that need to keep track
of both source and dest.
Anyway, I disagree and commit here. I will change to map_off and think
about the other cases.
There are also some more complex cases in which copying the map
and work with it avoids other bugs that I will have to think about:
- patch 9 ("drm/i915/guc: Convert engine record to
iosys_map"): as you already noticed we delegate its update to
other compilation unit
- patch 11 ("drm/i915/guc: Convert golden context prep to iosys_map"):
info_map, which can point either to the real buffer (in system
or IO memory) or to a temporary buffer (system memory)
- patch 17: it needs to write to 2 parts of struct: passing
different offsets depending on the call is IMO more error
prone than making sure we are working with the right variable.
thanks
Lucas De Marchi
I think this pattern should be applied to all similar code. As you
already noted, iosys_map_incr() is problematic.
Best regards
Thomas
+ }
+
+ return 0;
+}
+
int shmem_read(struct file *file, loff_t off, void *dst, size_t len)
{
return __shmem_rw(file, off, dst, len, false);
diff --git a/drivers/gpu/drm/i915/gt/shmem_utils.h b/drivers/gpu/drm/i915/gt/shmem_utils.h
index c1669170c351..e1784999faee 100644
--- a/drivers/gpu/drm/i915/gt/shmem_utils.h
+++ b/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 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);
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev
