On 9.5.2019 13.32, Marek Szyprowski wrote:
Dear All,
On 2019-04-26 15:23, Mathias Nyman wrote:
From: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
Immediate data transfers (IDT) allow the HCD to copy small chunks of
data (up to 8bytes) directly into its output transfer TRBs. This avoids
the somewhat expensive DMA mappings that are performed by default on
most URBs submissions.
In the case an URB was suitable for IDT. The data is directly copied
into the "Data Buffer Pointer" region of the TRB and the IDT flag is
set. Instead of triggering memory accesses the HC will use the data
directly.
The implementation could cover all kind of output endpoints. Yet
Isochronous endpoints are bypassed as I was unable to find one that
matched IDT's constraints. As we try to bypass the default DMA mappings
on URB buffers we'd need to find a Isochronous device with an
urb->transfer_buffer_length <= 8 bytes.
The implementation takes into account that the 8 byte buffers provided
by the URB will never cross a 64KB boundary.
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
Reviewed-by: Felipe Balbi <felipe.balbi@xxxxxxxxxxxxxxx>
Signed-off-by: Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx>
I've noticed that this patch causes regression on various Samsung Exynos
5420/5422/5800 boards, which have USB3.0 host ports provided by
DWC3/XHCI hardware module. The regression can be observed with ASIX USB
2.0 ethernet dongle, which stops working after applying this patch (eth0
interface is registered, but no packets are transmitted/received). I can
provide more debugging information or do some tests, just let me know
what do you need. Reverting this commit makes ASIX USB ethernet dongle
operational again.
Thanks for reporting.
Would it be possible to check if your ASIX ethernet dongle works on some
desktop/laptop setup with this same IDT patch?
Also Exynos xhci traces could help, they would show the content of the TRBs using IDT.
Maybe byte order gets messed up?
Take traces with:
mount -t debugfs none /sys/kernel/debug
echo 81920 > /sys/kernel/debug/tracing/buffer_size_kb
echo 1 > /sys/kernel/debug/tracing/events/xhci-hcd/enable
<connect ASIX eth dongle, try to use it>
send /sys/kernel/debug/tracing/trace content to me
If we can't get this fixed I'll revert the IDT patch
Thanks
Mathias
