Forgot to CC linux-usb.
-------- Forwarded Message --------
Subject: Re: howto debug xhci driver?
Date: Tue, 20 Mar 2018 13:56:21 -0700
From: Paul Zimmerman <pauldzim@xxxxxxxxx>
To: Bin Liu <b-liu@xxxxxx>
CC: Felipe Balbi <felipe.balbi@xxxxxxxxxxxxxxx>
Hi,
Bin Liu <b-liu@xxxxxx> writes:
Bin Liu <b-liu@xxxxxx> writes:
BTY, the issue I am trying to debug is when reading
bulk IN data from a USB2.0 device, if the device
doesn't have data to transmit and NAKs the IN packet,
after 4 pairs of IN-NAK transactions, xhci stops
sending further IN tokens until the next SOF, which
leaves ~90us gape on the bus.
But when reading data from a USB2.0 thumb drive, this
issue doesn't happen, even if the device NAKs the IN
tokens, xhci still keeps sending IN tokens, which is
way more than 4 pairs of IN-NAK transactions.
Thumb drive has Bulk endpoints, what is the other
device's transfer type?
It is bulk too. I asked for device descriptors. This is a
remote debug effort for me, I don't have that device...
Any one has a clue on what causes xhci to stop sending
IN tokens after the device NAK'd 4 times?
By accident, I reproduced the issue if addng a hub in the
middle... any comments about why a hub changes this xhci
behavior is appreciated.
none off the top of my head. Maybe Mathias can suggest
something.
The issue seems to be not related to how many bulk IN-NAK pairs
before host stops sending IN token, but the host stops IN token
if 1) the device ever NAK'd an bulk IN token, and 2) there is
about 90~100us left to the next SOF. Then all the rest of
bandwidth is wasted.
Is it about xhci bandwidth schduling? /me started reading...
is this AM4 or AM5? Perhaps go after Synopsys' known errata list?
I see the issue on both AM4 & AM5. I don't have access to the errata
list, I guess I should talk to TI internal for the list?
I have a hazy recollection of something like this being a "feature" of
the Synopsys core, to cut down on the excessive number of IN-NAK
transactions you can sometimes get on the USB bus. So yep, you
should talk to your Synopsys guy about this.
--
Paul
--
To unsubscribe from this list: send the line "unsubscribe linux-usb" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
