linux-kernel - Re: [PATCH v4 14/14] tty: gunyah: Add tty console driver for RM Console Services

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Date:   Fri, 7 Oct 2022 09:40:52 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Elliot Berman <quic_eberman@...cinc.com>
Cc:     Bjorn Andersson <quic_bjorande@...cinc.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Murali Nalajala <quic_mnalajal@...cinc.com>,
        Trilok Soni <quic_tsoni@...cinc.com>,
        Srivatsa Vaddagiri <quic_svaddagi@...cinc.com>,
        Carl van Schaik <quic_cvanscha@...cinc.com>,
        Andy Gross <agross@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Jassi Brar <jassisinghbrar@...il.com>,
        linux-arm-kernel@...ts.infradead.org,
        Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Marc Zyngier <maz@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Jonathan Corbet <corbet@....net>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Arnd Bergmann <arnd@...db.de>, devicetree@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 14/14] tty: gunyah: Add tty console driver for RM
 Console Services

On Thu, Oct 06, 2022 at 10:59:51PM -0700, Elliot Berman wrote:
> > > + */
> > > +#define RSC_MGR_TTY_ADAPTERS		16
> > 
> > We can have dynamic tty devices, so I don't understand this comment.
> > What really is the problem here?
> > 
> 
> Yes, I see the confusion. Dynamic device addition of tty devices is
> supported. As I understand, you need to know the maximum number of lines
> that could be added, and that is limitation I was referring to.

What do you mean by "lines"?  That's not a tty kernel term.

> Is this comment better?
> 
> The Linux TTY code requires us to know ahead of time how many lines we
> might need. Each line here corresponds to a VM. 16 seems like a
> reasonable number of lines for systems that are running Gunyah and using
> the provided console interface.

Again, line?  Do you mean port?

> > > +	cons_data->tty_driver->driver_name = "gh";

KBUILD_MODNAME?

> > > +	cons_data->tty_driver->name = "ttyGH";
> > 
> > Where did you pick this name from?
> > 
> > Where is it documented?
> > 
> 
> "GH" is the shorthand we've been using for "Gunyah". I didn't find
> documentation for dynamically assigned char devices, but if it exists, I can
> add entry for ttyGH.

Why use a new name at all?  Why not stick with the existing tty names
and device numbers?

thanks,

greg k-h