fw_setenv: fix bug when SPI flash write size != sector size

Some SPI flash have a write size that is different (smaller) than the
sector size. For example, the sst25vf016b has an erase size of 4096,
but a write size of 1 byte. For this flash device, the write()
function will be called with a size equal to the sector size of 4096,
and the return value will incorrectly be set to 4096, indicating that
4096 bytes have been written to the device. However, after inspecting
the flash content, only the first byte is written to the device, and
the remaining 4095 bytes are all 0xFF.

Fix this incorrect behavior by adapting mtdwrite() to use the write
size obtained from the MEMGETINFO ioctl when writing data.

Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Reviewed-by: Stefano Babic <sbabic@denx.de>

src/uboot_env.c

@@ -712,6 +712,8 @@ static int mtdwrite(struct uboot_flash_env *dev, void *data)
 		sectors = dev->envsectors ? dev->envsectors : 1;
 		buf = data;
 		while (count > 0) {
+			int blockcount;
+
 			erase.start = start;
 
 			skip = is_nand_badblock(dev, start);
@@ -742,17 +744,26 @@ static int mtdwrite(struct uboot_flash_env *dev, void *data)
 				ret =-EIO;
 				goto devwrite_out;
 			}
-			if (lseek(dev->fd, start, SEEK_SET) < 0) {
-				ret =-EIO;
-				goto devwrite_out;
-			}
-			if (write(dev->fd, buf, blocksize) != blocksize) {
-				ret =-EIO;
-				goto devwrite_out;
+
+			blockcount = blocksize;
+
+			/* writesize can be different than the sector size. */
+
+			while (blockcount > 0) {
+				if (lseek(dev->fd, start, SEEK_SET) < 0) {
+					ret =-EIO;
+					goto devwrite_out;
+				}
+				if (write(dev->fd, buf, dev->mtdinfo.writesize) != dev->mtdinfo.writesize) {
+					ret =-EIO;
+					goto devwrite_out;
+				}
+
+				blockcount -= dev->mtdinfo.writesize;
+				start += dev->mtdinfo.writesize;
+				buf += dev->mtdinfo.writesize;
 			}
 			MTDLOCK(dev, &erase);
-			start += dev->sectorsize;
-			buf += blocksize;
 			count -= blocksize;
 			ret += blocksize;
 		}