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

[Greg Kroah-Hartman]

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