Re: [PATCH] qmi_wwan: support modify usbnet's rx_urb_size

Daniele Palmas [off-list ref] writes:

Il giorno lun 3 ago 2020 alle ore 11:49 Greg KH
[off-list ref] ha scritto:

quoted

Where does QMI_WDA_SET_DATA_FORMAT come from?

This is a request of Qualcomm proprietary protocol used, among other
things, to configure data aggregation for modems. There's an open
source userspace implementation in the libqmi project
(https://cgit.freedesktop.org/libqmi/tree/data/qmi-service-wda.json)

quoted

And the commit log says that this "depends on the chipset being used",
so why don't you know that at probe time, does the chipset change?  :)

Me too does not understand this, I let the author explain...

quoted

quoted

Currently there's a workaround for setting rx_urb_size i.e. changing
the network interface MTU: this is fine for most uses with qmap, but
there's the limitation that certain values (multiple of the endpoint
size) are not allowed.

Why not just set it really high to start with?  That should not affect
any older devices, as the urb size does not matter.  The only thing is
if it is too small that things can not move as fast as they might be
able to.

Yes, this was proposed in the past by Bjørn
(https://lists.freedesktop.org/archives/libqmi-devel/2020-February/003221.html),
but I was not sure about issues with old modems.

Ah, right.  Forgot about that.

Now I understand that there are no such issues, then I agree this is
the simplest solution: I've seen modems requiring as much as 49152,
but usually the default for qmap is <= 16384.

And, by the way, increasing the rx urb size is required also in
non-qmap mode, since the current value leads to babbling issues with
some chipsets (mine
https://www.spinics.net/lists/linux-usb/msg198025.html and Paul's
https://lists.freedesktop.org/archives/libqmi-devel/2020-February/003217.html),
so I think we should definitely increase this also for non-qmap mode.

Bjørn, what do you think?

I think we have good enough reasons to increase the rx urb size by
default.  Let's try.



Bjørn