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

[Bin Meng]

On Mon, Sep 16, 2019 at 4:10 PM Marek Vasut <marek.vasut at gmail.com> wrote:
>
> On 9/16/19 8:53 AM, Bin Meng wrote:
> > On Mon, Sep 16, 2019 at 6:24 AM Marek Vasut wrote:
> >>
> >> 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.
> >>
> >> ---
> >>  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 we blindly set blk to 240 for both non-dm usb and dm usb here,
>
> Blindly ?

So based on the comments you added (also in kernel commit
779b457f66e1), it looks to me we have to set 240 for whatever usb
storage devices. That suggests if usb_get_max_xfer_size() is
implemented by DM USB drivers (so far only EHCI and xHCI implemented
it) and return a value larger than 120KiB, some usb storage devices is
subject to break.

>
> > which makes usb_get_max_xfer_size() useless. Should we completely drop
> > the usb_get_max_xfer_size() call?
>
> No, I think we should keep it if we ever decided to start implementing
> quirks like US_FL_MAX_SECTORS_64 (cfr. Linux scsiglue.c).
>
> >>         if (ret < 0) {
> >> -               /* unimplemented, let's use default 20 */
> >> -               blk = 20;
> >> +               blk = 240;
> >>         } else {
> >>                 if (size > USHRT_MAX * 512)
> >>                         size = USHRT_MAX * 512;
> >> --

Regards,
Bin