diff options
| -rw-r--r-- | drivers/usb/storage/scsiglue.c | 19 |
1 files changed, 18 insertions, 1 deletions
diff --git a/drivers/usb/storage/scsiglue.c b/drivers/usb/storage/scsiglue.c index 90901861bfc0..9da1fb3d0ff4 100644 --- a/drivers/usb/storage/scsiglue.c +++ b/drivers/usb/storage/scsiglue.c @@ -565,7 +565,24 @@ static const struct scsi_host_template usb_stor_host_template = { /* lots of sg segments can be handled */ .sg_tablesize = SCSI_MAX_SG_CHAIN_SEGMENTS, - /* limit the total size of a transfer to 120 KB */ + + /* + * 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. + */ .max_sectors = 240, /* merge commands... this seems to help performance, but |