[U-Boot] [PATCH] [RFC] usb: storage: Limit transfer size to 120 kiB

[Marek Vasut]

Due to constant influx of more and more weird and broken USB sticks,
do as Linux does in commit 779b457f66e10de3471479373463b27fd308dc85

    usb: storage: scsiglue: further describe our 240 sector limit

    Just so we have some sort of documentation as to why
    we limit our Mass Storage transfers to 240 sectors,
    let's update the comment to make clearer that
    devices were found that would choke with larger
    transfers.

    While at that, also make sure to clarify that other
    operating systems have similar, albeit different,
    limits on mass storage transfers.

And reduce the maximum transfer length of USB storage to 120 kiB.

Signed-off-by: Marek Vasut <marek.vasut+renesas at gmail.com>
Cc: Bin Meng <bmeng.cn at gmail.com>
Cc: Simon Glass <sjg at chromium.org>
---
 common/usb_storage.c | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/common/usb_storage.c b/common/usb_storage.c
index 8c889bb1a6..130eab7832 100644
--- a/common/usb_storage.c
+++ b/common/usb_storage.c
@@ -943,21 +943,28 @@ static void usb_stor_set_max_xfer_blk(struct usb_device *udev,
 	int __maybe_unused ret;
 
 #if !CONFIG_IS_ENABLED(DM_USB)
-#ifdef CONFIG_USB_EHCI_HCD
 	/*
-	 * The U-Boot EHCI driver can handle any transfer length as long as
-	 * there is enough free heap space left, but the SCSI READ(10) and
-	 * WRITE(10) commands are limited to 65535 blocks.
+	 * Limit the total size of a transfer to 120 KB.
+	 *
+	 * Some devices are known to choke with anything larger. It seems like
+	 * the problem stems from the fact that original IDE controllers had
+	 * only an 8-bit register to hold the number of sectors in one transfer
+	 * and even those couldn't handle a full 256 sectors.
+	 *
+	 * Because we want to make sure we interoperate with as many devices as
+	 * possible, we will maintain a 240 sector transfer size limit for USB
+	 * Mass Storage devices.
+	 *
+	 * Tests show that other operating have similar limits with Microsoft
+	 * Windows 7 limiting transfers to 128 sectors for both USB2 and USB3
+	 * and Apple Mac OS X 10.11 limiting transfers to 256 sectors for USB2
+	 * and 2048 for USB3 devices.
 	 */
-	blk = USHRT_MAX;
-#else
-	blk = 20;
-#endif
+	blk = 240;
 #else
 	ret = usb_get_max_xfer_size(udev, (size_t *)&size);
 	if (ret < 0) {
-		/* unimplemented, let's use default 20 */
-		blk = 20;
+		blk = 240;
 	} else {
 		if (size > USHRT_MAX * 512)
 			size = USHRT_MAX * 512;
-- 
2.23.0.rc1