[PATCH] fastboot: Re-implement erase according to spec
Sam Protsenko
semen.protsenko at linaro.org
Thu Jan 9 19:47:15 CET 2020
Fastboot specification [1] requires MMC to be filled with 0xFF's on
"fastboot erase" command:
erase:%s Erase the indicated partition (clear to 0xFFs)
Current "fastboot erase" implementation uses actual MMC erase operation
blk_derase(), which can fill MMC either with 0x00 or 0xFF, depending on
used MMC controller; from [2]:
The content of an explicitly erased memory range shall be '0' or '1'
depending on different memory technology.
For example, on BeagleBoard X15 it fills memory with '0'.
Furthermore, the minimal amount of memory blk_derase() can erase is
"erase group size", and it's usually 512 KiB or more. So if we try to
erase some partition which is smaller than 512 KiB, "fastboot erase"
won't work at all, due to alignment. It's good practice to align all
partitions to "erase group size" boundary, but it's not a strict
requirement, so we just can't use blk_derase() due to this restriction.
In order to provide the consistent way to erase partitions, adhere to
the fastboot spec, and fix erasing of small partitions, let's use
regular MMC write operation and fill the partition with 0xFF.
[1] https://android.googlesource.com/platform/system/core/+/refs/tags/android-10.0.0_r25/fastboot/README.md#command-reference
[2] https://www.jedec.org/system/files/docs/JESD84-A441.pdf
Signed-off-by: Sam Protsenko <semen.protsenko at linaro.org>
---
drivers/fastboot/fb_mmc.c | 90 +++++++++++++++++++++++++--------------
1 file changed, 59 insertions(+), 31 deletions(-)
diff --git a/drivers/fastboot/fb_mmc.c b/drivers/fastboot/fb_mmc.c
index b0b19c5762..a965ebb5af 100644
--- a/drivers/fastboot/fb_mmc.c
+++ b/drivers/fastboot/fb_mmc.c
@@ -16,6 +16,7 @@
#include <div64.h>
#include <linux/compat.h>
#include <android_image.h>
+#include <mapmem.h>
#define FASTBOOT_MAX_BLK_WRITE 16384
@@ -48,12 +49,12 @@ static int part_get_info_by_name_or_alias(struct blk_desc *dev_desc,
}
/**
- * fb_mmc_blk_write() - Write/erase MMC in chunks of FASTBOOT_MAX_BLK_WRITE
+ * fb_mmc_blk_write() - Write MMC in chunks of FASTBOOT_MAX_BLK_WRITE.
*
* @block_dev: Pointer to block device
- * @start: First block to write/erase
+ * @start: First block to write
* @blkcnt: Count of blocks
- * @buffer: Pointer to data buffer for write or NULL for erase
+ * @buffer: Pointer to data buffer for write
*/
static lbaint_t fb_mmc_blk_write(struct blk_desc *block_dev, lbaint_t start,
lbaint_t blkcnt, const void *buffer)
@@ -66,19 +67,59 @@ static lbaint_t fb_mmc_blk_write(struct blk_desc *block_dev, lbaint_t start,
for (i = 0; i < blkcnt; i += FASTBOOT_MAX_BLK_WRITE) {
cur_blkcnt = min((int)blkcnt - i, FASTBOOT_MAX_BLK_WRITE);
- if (buffer) {
- if (fastboot_progress_callback)
- fastboot_progress_callback("writing");
- blks_written = blk_dwrite(block_dev, blk, cur_blkcnt,
- buffer + (i * block_dev->blksz));
- } else {
- if (fastboot_progress_callback)
- fastboot_progress_callback("erasing");
- blks_written = blk_derase(block_dev, blk, cur_blkcnt);
- }
+ if (fastboot_progress_callback)
+ fastboot_progress_callback("writing");
+ blks_written = blk_dwrite(block_dev, blk, cur_blkcnt,
+ buffer + (i * block_dev->blksz));
+ blk += blks_written;
+ blks += blks_written;
+ }
+ return blks;
+}
+
+/**
+ * fb_mmc_blk_erase() - Erase MMC by filling it with 0xFF's.
+ *
+ * @block_dev: Pointer to block device
+ * @start: First block to erase
+ * @blkcnt: Count of blocks
+ *
+ * Fastboot protocol requires erase operation to fill the MMC with 0xFF bytes.
+ * So we can't use blk_derase(), because it can fill MMC with 0x00. Also,
+ * blk_derase() operates on "erase group size" (usually 512 KiB or more), which
+ * can lead to inability to erase small partitions (due to alignment).
+ *
+ * Use fastboot buffer (filled with 0xFF) to write MMC with 0xFF's. The write
+ * will be performed in chunks of FASTBOOT_MAX_BLK_WRITE (if possible).
+ */
+static lbaint_t fb_mmc_blk_erase(struct blk_desc *block_dev, lbaint_t start,
+ lbaint_t blkcnt)
+{
+ lbaint_t blk = start;
+ lbaint_t blks_written;
+ lbaint_t cur_blkcnt;
+ lbaint_t blks = 0;
+ void *buf;
+ size_t buf_sz, buf_blks, i;
+
+ buf_sz = min((size_t)(FASTBOOT_MAX_BLK_WRITE * block_dev->blksz),
+ (size_t)CONFIG_FASTBOOT_BUF_SIZE);
+ buf_sz = ALIGN_DOWN(buf_sz, block_dev->blksz);
+ buf_blks = buf_sz / block_dev->blksz;
+ assert(buf_blks > 0);
+ buf = map_sysmem(CONFIG_FASTBOOT_BUF_ADDR, buf_sz);
+ memset(buf, 0xff, buf_sz);
+
+ for (i = 0; i < blkcnt; i += buf_blks) {
+ cur_blkcnt = min((int)blkcnt - i, buf_blks);
+ if (fastboot_progress_callback)
+ fastboot_progress_callback("erasing");
+ blks_written = blk_dwrite(block_dev, blk, cur_blkcnt, buf);
blk += blks_written;
blks += blks_written;
}
+
+ unmap_sysmem(buf);
return blks;
}
@@ -441,7 +482,7 @@ void fastboot_mmc_erase(const char *cmd, char *response)
int ret;
struct blk_desc *dev_desc;
disk_partition_t info;
- lbaint_t blks, blks_start, blks_size, grp_size;
+ lbaint_t blks;
struct mmc *mmc = find_mmc_device(CONFIG_FASTBOOT_FLASH_MMC_DEV);
if (mmc == NULL) {
@@ -464,27 +505,14 @@ void fastboot_mmc_erase(const char *cmd, char *response)
return;
}
- /* Align blocks to erase group size to avoid erasing other partitions */
- grp_size = mmc->erase_grp_size;
- blks_start = (info.start + grp_size - 1) & ~(grp_size - 1);
- if (info.size >= grp_size)
- blks_size = (info.size - (blks_start - info.start)) &
- (~(grp_size - 1));
- else
- blks_size = 0;
-
- printf("Erasing blocks " LBAFU " to " LBAFU " due to alignment\n",
- blks_start, blks_start + blks_size);
-
- blks = fb_mmc_blk_write(dev_desc, blks_start, blks_size, NULL);
-
- if (blks != blks_size) {
+ blks = fb_mmc_blk_erase(dev_desc, info.start, info.size);
+ if (blks != info.size) {
pr_err("failed erasing from device %d\n", dev_desc->devnum);
fastboot_fail("failed erasing from device", response);
return;
}
- printf("........ erased " LBAFU " bytes from '%s'\n",
- blks_size * info.blksz, cmd);
+ printf("........ erased " LBAFU " bytes from '%s'\n", blks * info.blksz,
+ cmd);
fastboot_okay(NULL, response);
}
--
2.24.0
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