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From: "Måns Rullgård" <mans@mansr.com>
To: Dan Williams <dcbw@redhat.com>
Cc: "Johan Hovold" <johan@kernel.org>, "Bjørn Mork" <bjorn@mork.no>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] USB: serial: option: set driver_info for SIM5218 and compatibles
Date: Tue, 19 Mar 2019 14:35:18 +0000	[thread overview]
Message-ID: <yw1xr2b3ylsp.fsf@mansr.com> (raw)
In-Reply-To: <6c89938b00ad289e1802f675bd00e288b1458d73.camel@redhat.com> (Dan Williams's message of "Tue, 19 Mar 2019 09:30:25 -0500")

Dan Williams <dcbw@redhat.com> writes:

> On Tue, 2019-03-19 at 13:43 +0100, Johan Hovold wrote:
>> On Tue, Mar 19, 2019 at 01:27:19PM +0100, Johan Hovold wrote:
>> > On Tue, Mar 19, 2019 at 12:25:53PM +0000, Måns Rullgård wrote:
>> > > Johan Hovold <johan@kernel.org> writes:
>> > > 
>> > > > On Tue, Mar 19, 2019 at 10:54:00AM +0000, Måns Rullgård wrote:
>> > > > > Johan Hovold <johan@kernel.org> writes:
>> > > > > > > Regardless, setting the NCTRL flag should be harmless.
>> > > > > > 
>> > > > > > Well, there are devices that depend on getting these
>> > > > > > requests, at least
>> > > > > > for the QMI interface. But we can always revert if anyone
>> > > > > > complains.
>> > > > > 
>> > > > > The QMI interface doesn't even pretend to be a uart.  The
>> > > > > other ones do,
>> > > > > but there isn't actually any real uart behind them.  For
>> > > > > instance, it
>> > > > > doesn't matter what baud rate one sets.
>> > > > 
>> > > > Sure, but some devices still require "DTR" to be set for the
>> > > > QMI
>> > > > interface, so there not being any real uart is no guarantee
>> > > > that there
>> > > > is no firmware that expects these calls.
>> > > 
>> > > Now I'm thoroughly confused.  The QMI interface has a completely
>> > > separate driver that creates a network device (if I'm reading the
>> > > code
>> > > correctly).
>> > 
>> > I was just giving an example of firmware sometimes doing unexpected
>> > things.
>> 
>> See 93725149794d ("net: qmi_wwan: MDM9x30 specific power management")
>> for some background.
>
> TLDR; some firmware uses the DTR signal as an indicator to come out of
> low-power mode. Without doing so you cannot talk to the modem over any
> of it's ports, QMI, net, or serial.

I must be missing something, but how does a network interface have a DTR
signal?

-- 
Måns Rullgård

WARNING: multiple messages have this Message-ID (diff)
From: "Måns Rullgård" <mans@mansr.com>
To: Dan Williams <dcbw@redhat.com>
Cc: "Johan Hovold" <johan@kernel.org>, "Bjørn Mork" <bjorn@mork.no>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: USB: serial: option: set driver_info for SIM5218 and compatibles
Date: Tue, 19 Mar 2019 14:35:18 +0000	[thread overview]
Message-ID: <yw1xr2b3ylsp.fsf@mansr.com> (raw)

Dan Williams <dcbw@redhat.com> writes:

> On Tue, 2019-03-19 at 13:43 +0100, Johan Hovold wrote:
>> On Tue, Mar 19, 2019 at 01:27:19PM +0100, Johan Hovold wrote:
>> > On Tue, Mar 19, 2019 at 12:25:53PM +0000, Måns Rullgård wrote:
>> > > Johan Hovold <johan@kernel.org> writes:
>> > > 
>> > > > On Tue, Mar 19, 2019 at 10:54:00AM +0000, Måns Rullgård wrote:
>> > > > > Johan Hovold <johan@kernel.org> writes:
>> > > > > > > Regardless, setting the NCTRL flag should be harmless.
>> > > > > > 
>> > > > > > Well, there are devices that depend on getting these
>> > > > > > requests, at least
>> > > > > > for the QMI interface. But we can always revert if anyone
>> > > > > > complains.
>> > > > > 
>> > > > > The QMI interface doesn't even pretend to be a uart.  The
>> > > > > other ones do,
>> > > > > but there isn't actually any real uart behind them.  For
>> > > > > instance, it
>> > > > > doesn't matter what baud rate one sets.
>> > > > 
>> > > > Sure, but some devices still require "DTR" to be set for the
>> > > > QMI
>> > > > interface, so there not being any real uart is no guarantee
>> > > > that there
>> > > > is no firmware that expects these calls.
>> > > 
>> > > Now I'm thoroughly confused.  The QMI interface has a completely
>> > > separate driver that creates a network device (if I'm reading the
>> > > code
>> > > correctly).
>> > 
>> > I was just giving an example of firmware sometimes doing unexpected
>> > things.
>> 
>> See 93725149794d ("net: qmi_wwan: MDM9x30 specific power management")
>> for some background.
>
> TLDR; some firmware uses the DTR signal as an indicator to come out of
> low-power mode. Without doing so you cannot talk to the modem over any
> of it's ports, QMI, net, or serial.

I must be missing something, but how does a network interface have a DTR
signal?

  reply	other threads:[~2019-03-19 14:35 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-26 17:07 [PATCH] USB: serial: option: set driver_info for SIM5218 and compatibles Mans Rullgard
2019-02-26 17:07 ` Måns Rullgård
2019-02-27  8:33 ` [PATCH] " Johan Hovold
2019-02-27  8:33   ` Johan Hovold
2019-02-27 11:57   ` [PATCH] " Måns Rullgård
2019-02-27 11:57     ` Måns Rullgård
2019-02-27 13:13     ` [PATCH] " Johan Hovold
2019-02-27 13:13       ` Johan Hovold
2019-02-27 14:32       ` [PATCH] " Måns Rullgård
2019-02-27 14:32         ` Måns Rullgård
2019-03-18 14:32         ` [PATCH] " Måns Rullgård
2019-03-18 14:32           ` Måns Rullgård
2019-03-19 10:28         ` [PATCH] " Johan Hovold
2019-03-19 10:28           ` Johan Hovold
2019-03-19 10:54           ` [PATCH] " Måns Rullgård
2019-03-19 10:54             ` Måns Rullgård
2019-03-19 11:08             ` [PATCH] " Johan Hovold
2019-03-19 11:08               ` Johan Hovold
2019-03-19 12:25               ` [PATCH] " Måns Rullgård
2019-03-19 12:25                 ` Måns Rullgård
2019-03-19 12:27                 ` [PATCH] " Johan Hovold
2019-03-19 12:27                   ` Johan Hovold
2019-03-19 12:43                   ` [PATCH] " Johan Hovold
2019-03-19 12:43                     ` Johan Hovold
2019-03-19 14:30                     ` [PATCH] " Dan Williams
2019-03-19 14:30                       ` Dan Williams
2019-03-19 14:35                       ` Måns Rullgård [this message]
2019-03-19 14:35                         ` Måns Rullgård
2019-03-19 14:59                         ` [PATCH] " Bjørn Mork
2019-03-19 14:59                           ` Bjørn Mork
2019-03-19 16:26                           ` [PATCH] " Måns Rullgård
2019-03-19 16:26                             ` Måns Rullgård
2019-03-19 17:15                             ` [PATCH] " Bjørn Mork
2019-03-19 17:15                               ` Bjørn Mork

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