[PATCH v2] lib: sparse: allocate FASTBOOT_MAX_BLK_WRITE instead of small number

[Mattijs Korpershoek <mkorpershoek@baylibre.com>]

Commit 62649165cb02 ("lib: sparse: Make CHUNK_TYPE_RAW buffer aligned")
fixed cache alignment for systems with a D-CACHE.

However it introduced some performance regressions [1] on system
flashing huge images, such as Android.

On AM62x SK EVM, we also observe such performance penalty:
Sending sparse 'super' 1/2 (768793 KB)             OKAY [ 23.954s]
Writing 'super'                                    OKAY [ 75.926s]
Sending sparse 'super' 2/2 (629819 KB)             OKAY [ 19.641s]
Writing 'super'                                    OKAY [ 62.849s]
Finished. Total time: 182.474s

The reason for this is that we use an arbitrary small buffer
(info->blksz * 100) for transferring.

Fix it by using a bigger buffer (info->blksz * FASTBOOT_MAX_BLK_WRITE)
as suggested in the original's patch review [2].

With this patch, performance impact is mitigated:
Sending sparse 'super' 1/2 (768793 KB)             OKAY [ 23.912s]
Writing 'super'                                    OKAY [ 15.780s]
Sending sparse 'super' 2/2 (629819 KB)             OKAY [ 19.581s]
Writing 'super'                                    OKAY [ 17.192s]
Finished. Total time: 76.569s

[1] https://lore.kernel.org/r/20221118121323.4009193-1-gary.bisson@boundarydevices.com
[2] https://lore.kernel.org/r/all/43e4c17c-4483-ec8e-f843-9b4c5569bd18@seco.com/

Fixes: 62649165cb02 ("lib: sparse: Make CHUNK_TYPE_RAW buffer aligned")
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
---
Changes in v2:
- Use FASTBOOT_MAX_BLK_WRITE instead of blkcnt (Qianfan)
- Link to v1: https://lore.kernel.org/r/20230616-sparse-flash-fix-v1-1-6bafeacc567b@baylibre.com
---
 drivers/fastboot/fb_mmc.c | 2 --
 include/image-sparse.h    | 2 ++
 lib/image-sparse.c        | 3 ++-
 3 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/fastboot/fb_mmc.c b/drivers/fastboot/fb_mmc.c
index 9d25c402028a..060918e49109 100644
--- a/drivers/fastboot/fb_mmc.c
+++ b/drivers/fastboot/fb_mmc.c
@@ -19,8 +19,6 @@
 #include <linux/compat.h>
 #include <android_image.h>
 
-#define FASTBOOT_MAX_BLK_WRITE 16384
-
 #define BOOT_PARTITION_NAME "boot"
 
 struct fb_mmc_sparse {
diff --git a/include/image-sparse.h b/include/image-sparse.h
index 0572dbd0a283..282a0b256498 100644
--- a/include/image-sparse.h
+++ b/include/image-sparse.h
@@ -7,6 +7,8 @@
 #include <part.h>
 #include <sparse_format.h>
 
+#define FASTBOOT_MAX_BLK_WRITE 16384
+
 #define ROUNDUP(x, y)	(((x) + ((y) - 1)) & ~((y) - 1))
 
 struct sparse_storage {
diff --git a/lib/image-sparse.c b/lib/image-sparse.c
index 5ec0f94ab3eb..8f8a67e15804 100644
--- a/lib/image-sparse.c
+++ b/lib/image-sparse.c
@@ -55,7 +55,8 @@ static lbaint_t write_sparse_chunk_raw(struct sparse_storage *info,
 				       void *data,
 				       char *response)
 {
-	lbaint_t n = blkcnt, write_blks, blks = 0, aligned_buf_blks = 100;
+	lbaint_t n = blkcnt, write_blks, blks = 0;
+	lbaint_t aligned_buf_blks = FASTBOOT_MAX_BLK_WRITE;
 	uint32_t *aligned_buf = NULL;
 
 	if (CONFIG_IS_ENABLED(SYS_DCACHE_OFF)) {

---
base-commit: 923de765ee1a5b26310f02cb42dcbad9e2b011c5
change-id: 20230616-sparse-flash-fix-9c2852aa8d16

Best regards,
-- 
Mattijs Korpershoek <mkorpershoek@baylibre.com>