答复: Quectel EG21 modem QMI connection works but MM fallbacks to ttyUSB2 as primary port

[Carl Yin(殷张成)]

Hi Rafal:
	For you are using EC21, the upstream qmi_wwan driver is enough.
	If the EC21's VID and PID is not in the qmi_wwan.c products table, you just need add it, as next:
	{QMI_QUIRK_SET_DTR(0x2c7c, 0x0121, 4)},	/* Quectel EC21 Mini PCIe */

	If you are using LTE-A or 5G modules, it is recomment to use MBIM (set by at+qcfg="usbnet", 2 )
	(for these modems, it is recomment or mandatory to use "QMAP" fucntion, but not well support by the upsream qmi_wwan)

Hi Aleksander:
	Quectel has lot of customers, and most of them are use system like openwrt, android, others embedded -linux. 
	and the kernel version used is usually is V3.x,V4.x.
	it will spend very much time (for quectel-self and customers):
			 if we appiled patch to the upstream qmi_wwan driver, and back-port the driver to the customer's kernel.
	So we directly povide qmi_wwan_q.c, suitable for ALL kernel versions (V3.2 and later), the customers just need 'copy + paste' it.
	

On November 26, 2020 1:22 AM, Aleksander wrote:

> Hey Rafal!
> 
> > Jan  1 04:51:00 zubrOS ModemManager[342]: <debug> [000017460.859237]
> [filter]   cdc-wdm devices allowed:    yes
> > Jan  1 04:51:35 zubrOS kernel: [   54.178239] qmi_wwan_q 1-1:1.4: cdc-wdm0:
> USB WDM device
> 
> I saw your merge request and replied about that there, the problem you had
> with ModemManager not detecting the cdc-wdm port as a QMI port was indeed
> the kernel driver name, "qmi_wwan_q" vs "qmi_wwan":
> https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/merge_re
> quests/406
> 
> It's really unfortunate that the vendors try to push their own modified kernel
> drivers, instead of making sure the upstream one is properly up to date to
> support their modules. There should be no reason for that to happen, and we
> shouldn't enforce that approach in ModemManager.
> 
> @Carl Yin(殷张成) what is the reason for Quectel to suggest using a custom
> modified "qmi_wwan_q" driver instead of suggesting to use the upstream
> default one? How can we help solve this?
> 
> --
> Aleksander
> https://aleksander.es
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