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Date: Mon, 10 Oct 2022 22:23:29 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Elliot Berman <quic_eberman@...cinc.com>
Cc: Jiri Slaby <jirislaby@...nel.org>,
Bjorn Andersson <quic_bjorande@...cinc.com>,
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>,
Prakruthi Deepak Heragu <quic_pheragu@...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 Sun, Oct 09, 2022 at 01:59:21PM -0700, Elliot Berman wrote:
>
>
> On 10/7/2022 12:40 AM, Greg Kroah-Hartman wrote:
> > On Thu, Oct 06, 2022 at 10:59:51PM -0700, Elliot Berman wrote:
> > >
> > > "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?
> >
>
> I can use hvc framework, although driver-level buffering is needed on
> both the get_chars/put_chars paths because:
I'm not asking about the framework (although that is a good question,
you need to document why this has to be new.) I'm asking why pick a new
name? You will not have a name conflict in your system with this device
with any other tty name right?
> - get_chars wants to poll for characters, but Gunyah will push
> characters to Linux
> - put_chars can be called in atomic context in the printk console path.
> Gunyah RM calls can sleep, so we add to buffer and queue work to
> write the characters.
>
> I also chose to use new tty driver because the Gunyah hypervisor call to
> open the console (gh_rm_console_open) can only be done after starting the
> VM. Gunyah will only forward characters sent from the other VM to Linux
> after the gh_rm_console_open call is made. When launching a VM, users would
> want to open console before VM starts so they can get startup messages from
> the VM. I planned to use the carrier_raised() to hold
> tty_port_block_until_ready until the VM is started and the
> gh_rm_console_open() happens.
I'm sorry, but I don't understand this.
Why is this all a new api at all? What about the virtio api? Why not
just use that instead?
thanks,
greg k-h
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