netdev - Re: [PATCH net-next 1/1] net: wwan: t7xx: Add AP CLDMA and GNSS port

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Date:   Tue, 21 Jun 2022 09:45:01 -0700
From:   "moises.veleta" <moises.veleta@...ux.intel.com>
To:     Sergey Ryazanov <ryazanov.s.a@...il.com>
Cc:     Loic Poulain <loic.poulain@...aro.org>, netdev@...r.kernel.org,
        Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...emloft.net>,
        Johannes Berg <johannes@...solutions.net>,
        M Chetan Kumar <m.chetan.kumar@...el.com>,
        "Devegowda, Chandrashekar" <chandrashekar.devegowda@...el.com>,
        Intel Corporation <linuxwwan@...el.com>,
        chiranjeevi.rapolu@...ux.intel.com,
        Haijun Liu (刘海军) 
        <haijun.liu@...iatek.com>,
        Ricardo Martinez <ricardo.martinez@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "Sharma, Dinesh" <dinesh.sharma@...el.com>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        "Veleta, Moises" <moises.veleta@...el.com>,
        Madhusmita Sahu <madhusmita.sahu@...el.com>
Subject: Re: [PATCH net-next 1/1] net: wwan: t7xx: Add AP CLDMA and GNSS port


On 6/18/22 04:55, Sergey Ryazanov wrote:
> Hello Moises,
>
> On Fri, Jun 17, 2022 at 8:28 PM moises.veleta
> <moises.veleta@...ux.intel.com> wrote:
>> On 6/16/22 10:29, Loic Poulain wrote:
>>> Hi Moises,
>>>
>>> On Tue, 14 Jun 2022 at 22:58, Moises Veleta
>>> <moises.veleta@...ux.intel.com> wrote:
>>>> From: Haijun Liu <haijun.liu@...iatek.com>
>>>>
>>>> The t7xx device contains two Cross Layer DMA (CLDMA) interfaces to
>>>> communicate with AP and Modem processors respectively. So far only
>>>> MD-CLDMA was being used, this patch enables AP-CLDMA and the GNSS
>>>> port which requires such channel.
>>>>
>>>> Signed-off-by: Haijun Liu <haijun.liu@...iatek.com>
>>>> Co-developed-by: Madhusmita Sahu <madhusmita.sahu@...el.com>
>>>> Signed-off-by: Madhusmita Sahu <madhusmita.sahu@...el.com>
>>>> Signed-off-by: Moises Veleta <moises.veleta@...ux.intel.com>
>>>> ---
>>> [...]
>>>>    static const struct t7xx_port_conf t7xx_md_port_conf[] = {
>>>>           {
>>>> +               .tx_ch = PORT_CH_AP_GNSS_TX,
>>>> +               .rx_ch = PORT_CH_AP_GNSS_RX,
>>>> +               .txq_index = Q_IDX_CTRL,
>>>> +               .rxq_index = Q_IDX_CTRL,
>>>> +               .path_id = CLDMA_ID_AP,
>>>> +               .ops = &wwan_sub_port_ops,
>>>> +               .name = "t7xx_ap_gnss",
>>>> +               .port_type = WWAN_PORT_AT,
>>> Is it really AT protocol here? wouldn't it be possible to expose it
>>> via the existing GNSS susbsystem?
>> The protocol is AT.
>> It is not possible to using the GNSS subsystem as it is meant for
>> stand-alone GNSS receivers without a control path. In this case, GNSS
>> can used for different use cases, such as Assisted GNSS, Cell ID
>> positioning, Geofence, etc. Hence, this requires the use of the AT
>> channel on the WWAN subsystem.
> To make it clear. When you talking about a control path, did you mean
> that this GNSS port is not a simple NMEA port? Or did you mean that
> this port is NMEA, but the user is required to activate GPS
> functionality using the separate AT-commands port?
>
> In other words, what is the format of the data that are transmitted
> over the GNSS port of the modem?
>
It is an AT port where MTK GNSS AT commands can be sent and received. 
Not a simple NMEA port, but NMEA data can be sent to Host via an AT 
command. Control port is exposed for Modem Manager to send GNSS comands, 
which may include disable/enable GPS functionality (enabled by default).

These are MTK GNSS AT commands, which follow the syntax as defined by 
3GPP TS 27.007.  These are not standard AT commands.


Regards,
Moises