netdev - Re: [PATCH] qmi_wwan: support modify usbnet's rx_urb

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Date:   Mon, 03 Aug 2020 12:40:54 +0200
From:   Bjørn Mork <bjorn@...k.no>
To:     Daniele Palmas <dnlplm@...il.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>, yzc666@...ease.com,
        David Miller <davem@...emloft.net>, kuba@...nel.org,
        netdev@...r.kernel.org, linux-usb <linux-usb@...r.kernel.org>,
        carl <carl.yin@...ctel.com>
Subject: Re: [PATCH] qmi_wwan: support modify usbnet's rx_urb_size

Daniele Palmas <dnlplm@...il.com> writes:
> Il giorno lun 3 ago 2020 alle ore 11:49 Greg KH
> <gregkh@...uxfoundation.org> ha scritto:
>>
>> 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)
>
>> 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...
>
>> > 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