linux-kernel - Re: [PATCH] virtio: console: Prepare for making REMOTEPROC modular

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Message-ID: <535ivi67jdmcuhns5q4r36fjpqde3clnqq7hr26gmg33jwoxyb@ahvuhhaewh3u>
Date: Fri, 14 Feb 2025 18:47:07 +0100
From: Uwe Kleine-König <u.kleine-koenig@...libre.com>
To: Amit Shah <amit@...nel.org>
Cc: Arnd Bergmann <arnd@...db.de>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virtio: console: Prepare for making REMOTEPROC modular

On Fri, Feb 14, 2025 at 05:55:41PM +0100, Amit Shah wrote:
> On Fri, 2025-02-14 at 17:52 +0100, Uwe Kleine-König wrote:
> > Hello Amit,
> > 
> > On Fri, Feb 14, 2025 at 05:37:52PM +0100, Amit Shah wrote:
> > > I'm thinking of the two combinations of interest: REMOTEPROC=m,
> > > VIRTIO_CONSOLE can be y or m.  Say virtcons_probe() happens when
> > > the
> > > remoteproc module isn't yet loaded.  Even after later loading
> > > remoteproc, virtio console won't do anything interesting with
> > > remoteproc.
> > 
> > Where does the interesting thing happen if remoteproc is already
> > loaded
> > at that time? I'm not seeing anything interesting in that case either
> > ...
> 
> The code I pointed to,
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/char/virtio_console.c#n1993
> 
> either enables remoteproc if the module is present; or it enables
> multiport, but not both at the same time.  If remoteproc isn't present
> when this probe routine is executed, multiport might get enabled.  And
> then there's no chance for remoteproc to get enabled.

The only case where there is a difference between IS_REACHABLE and
IS_ENABLED is:

	CONFIG_REMOTEPROC=m
	CONFIG_VIRTIO_CONSOLE=y

Iff in this case you never want to test for MULTIPORT (even though the
remoteproc module might never get loaded), then my patch is wrong.

When creating the patch I thought there is a hard dependency on
remoteproc (like calling a function that is provided by
CONFIG_REMOTEPROC). I don't understand how the remoteproc stuff
interacts with the virtio_console driver, is this something in userspace
which then would also autoload the remoteproc module?

Best regards
Uwe

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