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Message-ID: <615493a8-449d-b105-709e-0642dfb5359b@quicinc.com>
Date: Sun, 9 Oct 2022 13:59:21 -0700
From: Elliot Berman <quic_eberman@...cinc.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jiri Slaby <jirislaby@...nel.org>
CC: 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 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:
- 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.
Thanks,
Elliot
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