On Fri, 15 Apr 2016, Felipe Balbi wrote:
> Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> writes:
> > On Thu, 14 Apr 2016, Felipe Balbi wrote:
> >
> >> >> --- a/drivers/usb/storage/scsiglue.c
> >> >> +++ b/drivers/usb/storage/scsiglue.c
> >> >> @@ -127,6 +127,11 @@ static int slave_configure(struct scsi_device *sdev)
> >> >> if (queue_max_hw_sectors(sdev->request_queue) > max_sectors)
> >> >> blk_queue_max_hw_sectors(sdev->request_queue,
> >> >> max_sectors);
> >> >> + } else if (us->pusb_dev->speed >= USB_SPEED_SUPER) {
> >> >> + /* USB3 devices will be limited to 2048 sectors. This gives us
> >> >> + * better throughput on most devices.
> >> >> + */
> >> >> + blk_queue_max_hw_sectors(sdev->request_queue, 2048);
> >> >> } else if (sdev->type == TYPE_TAPE) {
> >> >> /* Tapes need much higher max_sector limits, so just
> >> >> * raise it to the maximum possible (4 GB / 512) and
> >> >
> >> > Argh! This has the same kind of problem as before. What will happen
> >> > when somebody has a USB-3 tape drive?
> >>
> >> I didn't know that was even plausible :-) Anyway, I'll update, but while
> >> at that, so I use for bcdUSB instead of speed as Oliver suggested ? I
> >> mean, a USB3 stick running on high-speed can also support 2048 max
> >> sectors, right ?
> >>
> >> let me know
> >
> > To tell the truth, I have no idea. There probably aren't enough USB-3
> > products in existence yet to tell -- not to mention that with the
> > existing code, we wouldn't detect any exceptions.
> >
> > It sounds reasonable... But won't a USB-3 device running at high speed
> > provide a device descriptor that has bcdUSB set to 0x0210? (See the
> > second paragraph of section 9.6.1 in the USB-3.1 spec.)
>
> right, but an HS USB 2.1 device is also recent enough that it's likely
> to work similarly, no ?
Again, I don't know. But in my experience, relying on USB device
designers to do things correctly tends not to work out. :-(
Besides, whether something works right has less to do with how recent
it is and more to do with whether or not it was ever tested. If
Windows doesn't transfer more than 240 sectors at a time at high speed
then we probably shouldn't either.
Alan Stern
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