netdev - Re: [PATCH net-next 3/3] ice: add write functionality for GNSS TTY

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Message-ID: <20220523105850.606a75c1@kernel.org>
Date:   Mon, 23 May 2022 10:58:50 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     "Kolacinski, Karol" <karol.kolacinski@...el.com>
Cc:     "davem@...emloft.net" <davem@...emloft.net>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "richardcochran@...il.com" <richardcochran@...il.com>,
        "G, GurucharanX" <gurucharanx.g@...el.com>,
        "Nguyen, Anthony L" <anthony.l.nguyen@...el.com>
Subject: Re: [PATCH net-next 3/3] ice: add write functionality for GNSS TTY

On Mon, 23 May 2022 16:56:44 +0000 Kolacinski, Karol wrote:
> On Thu, 19 May 2022 06:57 +0200 Jakub Kicinski wrote:
> > > Create a second read-only TTY device.  
> > 
> > Can you say more about how the TTY devices are discovered, and why there
> > are two of them? Would be great if that info was present under
> > Documentation/  
> 
> Both TTY devices are used for the same GNSS module. First one is
> read/write and the second one is read only. They are discovered by
> checking ICE_E810T_P0_GNSS_PRSNT_N bit in ICE_PCA9575_P0_IN register.
> This means that the GNSS module is physically present on the PCB.
> The design with one RW and one RO TTY device was requested by
> customers.

I meant discovered at the uAPI level. Imagine I plug in a shiny E810T
with a GNSS receiver into a box, the PRSNT_N bit is set and the driver
registered the ttys. How do I find the GNSS under /dev ?