[RFT PATCH v1 3/5] usb: Add some delay to wait for slow USB devices to be operational

Lukasz Majewski
2020-03-23T07:04:43Z

Hi Marek,

> On 3/22/20 2:00 PM, Lukasz Majewski wrote:
> > This change provides some extra time for some slow (or degraded)
> > USB devices to become fully operational.
> >
> > This code is the port to newest U-Boot of the fix from - "rayvt"
> > (from [1]).
> >
> > Links:
> > [1] - https://forum.doozan.com/read.php?3,35295,35295#msg-35295
> > [2] -
> > https://www.dropbox.com/s/nrkrd1no63viuu8/uboot-bodhi-2016.05-timeoutTD.patch?dl=0
> >
> > Signed-off-by: Lukasz Majewski <lukma@denx.de>
> > [Unfortunately, the original patch [2] did not contain S-o-B from
> > the original author - "rayvt"]
> > ---
> >
> > common/usb.c | 10 ++++++++--
> > 1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/common/usb.c b/common/usb.c
> > index 349e838f1d..305482b5bb 100644
> > --- a/common/usb.c
> > +++ b/common/usb.c
> > @@ -925,14 +925,20 @@ static int get_descriptor_len(struct
> > usb_device *dev, int len, int expect_len) __maybe_unused struct
> > usb_device_descriptor *desc; ALLOC_CACHE_ALIGN_BUFFER(unsigned
> > char, tmpbuf, USB_BUFSIZ); int err;
> > + int retry = 5;
> >
> > desc = (struct usb_device_descriptor *)tmpbuf;
> >
> > +again:
> > err = usb_get_descriptor(dev, USB_DT_DEVICE, 0, desc, len);
> > if (err < expect_len) {
> > if (err < 0) {
> > - printf("unable to get device descriptor
> > (error=%d)\n",
> > - err);
> > + printf("unable to get device descriptor
> > (error=%d) retry: %d\n",
> > + err, retry);
> > + mdelay(50);
>
> Why 50 mSec and not some other value, like 100 mSec ?

I think that this value (50 ms) was took from Linux in some point and
with the retry set to 5 was the ported heuristics.

If you ask why exactly there is 50 ms - I cannot say, as I've just
ported the patch.

Best regards,

Lukasz Majewski

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