Re: [PATCH 1/9] drm/xen-front: Introduce Xen para-virtualized frontend driver

[Oleksandr Andrushchenko]

On 02/21/2018 10:19 AM, Juergen Gross wrote:
> On 21/02/18 09:03, Oleksandr Andrushchenko wrote:
> > From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> >
> > Introduce skeleton of the para-virtualized Xen display
> > frontend driver. This patch only adds required
> > essential stubs.
> >
> > Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> > ---
> >   drivers/gpu/drm/Kconfig             |  2 +
> >   drivers/gpu/drm/Makefile            |  1 +
> >   drivers/gpu/drm/xen/Kconfig         | 17 ++++++++
> >   drivers/gpu/drm/xen/Makefile        |  5 +++
> >   drivers/gpu/drm/xen/xen_drm_front.c | 83 +++++++++++++++++++++++++++++++++++++
> >   5 files changed, 108 insertions(+)
> >   create mode 100644 drivers/gpu/drm/xen/Kconfig
> >   create mode 100644 drivers/gpu/drm/xen/Makefile
> >   create mode 100644 drivers/gpu/drm/xen/xen_drm_front.c
> >
> > diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> > index deeefa7a1773..757825ac60df 100644
> > --- a/drivers/gpu/drm/Kconfig
> > +++ b/drivers/gpu/drm/Kconfig
> > @@ -289,6 +289,8 @@ source "drivers/gpu/drm/pl111/Kconfig"
> >   
> >   source "drivers/gpu/drm/tve200/Kconfig"
> >   
> > +source "drivers/gpu/drm/xen/Kconfig"
> > +
> >   # Keep legacy drivers last
> >   
> >   menuconfig DRM_LEGACY
> > diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
> > index 50093ff4479b..9d66657ea117 100644
> > --- a/drivers/gpu/drm/Makefile
> > +++ b/drivers/gpu/drm/Makefile
> > @@ -103,3 +103,4 @@ obj-$(CONFIG_DRM_MXSFB)	+= mxsfb/
> >   obj-$(CONFIG_DRM_TINYDRM) += tinydrm/
> >   obj-$(CONFIG_DRM_PL111) += pl111/
> >   obj-$(CONFIG_DRM_TVE200) += tve200/
> > +obj-$(CONFIG_DRM_XEN) += xen/
> > diff --git a/drivers/gpu/drm/xen/Kconfig b/drivers/gpu/drm/xen/Kconfig
> > new file mode 100644
> > index 000000000000..4cca160782ab
> > --- /dev/null
> > +++ b/drivers/gpu/drm/xen/Kconfig
> > @@ -0,0 +1,17 @@
> > +config DRM_XEN
> > +	bool "DRM Support for Xen guest OS"
> > +	depends on XEN
> > +	help
> > +	  Choose this option if you want to enable DRM support
> > +	  for Xen.
> > +
> > +config DRM_XEN_FRONTEND
> > +	tristate "Para-virtualized frontend driver for Xen guest OS"
> > +	depends on DRM_XEN
> > +	depends on DRM
> > +	select DRM_KMS_HELPER
> > +	select VIDEOMODE_HELPERS
> > +	select XEN_XENBUS_FRONTEND
> > +	help
> > +	  Choose this option if you want to enable a para-virtualized
> > +	  frontend DRM/KMS driver for Xen guest OSes.
> > diff --git a/drivers/gpu/drm/xen/Makefile b/drivers/gpu/drm/xen/Makefile
> > new file mode 100644
> > index 000000000000..967074d348f6
> > --- /dev/null
> > +++ b/drivers/gpu/drm/xen/Makefile
> > @@ -0,0 +1,5 @@
> > +# SPDX-License-Identifier: GPL-2.0
> > +
> > +drm_xen_front-objs := xen_drm_front.o
> > +
> > +obj-$(CONFIG_DRM_XEN_FRONTEND) += drm_xen_front.o
> > diff --git a/drivers/gpu/drm/xen/xen_drm_front.c b/drivers/gpu/drm/xen/xen_drm_front.c
> > new file mode 100644
> > index 000000000000..fd372fb464a1
> > --- /dev/null
> > +++ b/drivers/gpu/drm/xen/xen_drm_front.c
> > @@ -0,0 +1,83 @@
> > +/*
> > + *  Xen para-virtual DRM device
> > + *
> > + *   This program is free software; you can redistribute it and/or modify
> > + *   it under the terms of the GNU General Public License as published by
> > + *   the Free Software Foundation; either version 2 of the License, or
> > + *   (at your option) any later version.
> > + *
> > + *   This program is distributed in the hope that it will be useful,
> > + *   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + *   GNU General Public License for more details.
> Use SPDX identifier instead (same applies for all other new
> sources):
>
> // SPDX-License-Identifier: GPL-2.0
Will update, thank you
> > + *
> > + * Copyright (C) 2016-2018 EPAM Systems Inc.
> > + *
> > + * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> > + */
> > +
> > +#include <drm/drmP.h>
> > +
> > +#include <xen/platform_pci.h>
> > +#include <xen/xen.h>
> > +#include <xen/xenbus.h>
> > +
> > +#include <xen/interface/io/displif.h>
> > +
> > +static void backend_on_changed(struct xenbus_device *xb_dev,
> > +		enum xenbus_state backend_state)
> > +{
> > +}
> > +
> > +static int xen_drv_probe(struct xenbus_device *xb_dev,
> > +		const struct xenbus_device_id *id)
> > +{
> > +	return 0;
> > +}
> > +
> > +static int xen_drv_remove(struct xenbus_device *dev)
> > +{
> > +	return 0;
> > +}
> > +
> > +static const struct xenbus_device_id xen_drv_ids[] = {
> > +	{ XENDISPL_DRIVER_NAME },
> > +	{ "" }
> > +};
> > +
> > +static struct xenbus_driver xen_driver = {
> > +	.ids = xen_drv_ids,
> > +	.probe = xen_drv_probe,
> > +	.remove = xen_drv_remove,
> > +	.otherend_changed = backend_on_changed,
> > +};
> > +
> > +static int __init xen_drv_init(void)
> > +{
> > +	if (!xen_domain())
> > +		return -ENODEV;
> > +
> > +	if (xen_initial_domain()) {
> > +		DRM_ERROR(XENDISPL_DRIVER_NAME " cannot run in initial domain\n");
> > +		return -ENODEV;
> > +	}
> Why not? Wouldn't that be possible in case of the backend living in a
> driver domain?
It is possible (and in my use-case backend indeed runs in
a driver domain). I was just not sure if it is really a
good idea to allow that. If you think this is ok, then
I'll remove this check
> Juergen
Thank you,
Oleksandr