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

[Oleksandr Andrushchenko <andr2000@xxxxxxxxx>]

On 02/21/2018 11:09 AM, Juergen Gross wrote:
> On 21/02/18 09:47, Oleksandr Andrushchenko wrote:
> > 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
> I don't think the driver should decide that. This would be the job of
> Xen tools IMO.
Agree, will remove
> Juergen

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