[XS] Change in flashrom[master]: linux_mtd.c: Optimise linux_mtd_wp_read_cfg() ioctl() calls

[Edward O'Callaghan (Code Review)]

Edward O'Callaghan has uploaded this change for review. ( https://review.coreboot.org/c/flashrom/+/75476?usp=email )

Change subject: linux_mtd.c: Optimise linux_mtd_wp_read_cfg() ioctl() calls
......................................................................

linux_mtd.c: Optimise linux_mtd_wp_read_cfg() ioctl() calls

The linux_mtd_wp_read_cfg() function makes excessive
ioctl() calls as it sweeps on a per-eraseblock basis.
Instead employ a bisection algorithm to optimise the
number of user to kernel interactions to a minimum.

Change-Id: I7ae3816598b74f0db7ac7d564391e69cfb8b1f79
Signed-off-by: Edward O'Callaghan 
Co-Authored-by: Damien Zammit 
---
M linux_mtd.c
1 file changed, 5 insertions(+), 2 deletions(-)

git pull ssh://review.coreboot.org:29418/flashrom refs/changes/76/75476/1

diff --git a/linux_mtd.c b/linux_mtd.c
index 495db9a..bc07dfa 100644
--- a/linux_mtd.c
+++ b/linux_mtd.c
@@ -323,7 +323,8 @@
    cfg->range.len = 0;

/* Check protection status of each block */
-	for (size_t u = 0; u < data->total_size; u += data->erasesize) {
+	uint32_t erase_boundary = total_size/2;
+	for (size_t u = 0; u < data->total_size; u += erase_boundary) {
    	struct erase_info_user erase_info = {
    		.start = u,
    		.length = data->erasesize,
@@ -339,13 +340,15 @@
    	} else if (ret == 1) {
    		/* Block is protected. */

-			if (end_found) {
+			if (end_found && (erase_boundary < data->erasesize)) {
    			/*
    			 * We already found the end of another
    			 * protection range, so this is the start of a
    			 * new one.
    			 */
    			return FLASHROM_WP_ERR_OTHER;
+			} else { /* hole to bisect */
+				erase_boundary = max(erase_boundary/2, data->erasesize);
    		}
    		if (!start_found) {
    			cfg->range.start = erase_info.start;