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Subject: Re: [PATCH 1/9] drm/xen-front: Introduce Xen para-virtualized
 frontend driver
To:     Oleksandr Andrushchenko <andr2000@gmail.com>,
        xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org, airlied@linux.ie,
        daniel.vetter@intel.com, seanpaul@chromium.org,
        gustavo@padovan.org, boris.ostrovsky@oracle.com,
        konrad.wilk@oracle.com
Cc:     Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
References: <1519200222-20623-1-git-send-email-andr2000@gmail.com>
 <1519200222-20623-2-git-send-email-andr2000@gmail.com>
 <c0928eaa-10e7-f047-dfe5-18e7cba76e76@suse.com>
 <91386840-c34a-31a4-2bb3-14a27ececa9c@gmail.com>
From:   Juergen Gross <jgross@suse.com>
Message-ID: <4b20fcdd-2618-71a8-d94e-37c802973a02@suse.com>
Date:   Wed, 21 Feb 2018 10:09:49 +0100
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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@epam.com>
>>>
>>> Introduce skeleton of the para-virtualized Xen display
>>> frontend driver. This patch only adds required
>>> essential stubs.
>>>
>>> Signed-off-by: Oleksandr Andrushchenko
>>> <oleksandr_andrushchenko@epam.com>
>>> ---
>>>   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@epam.com>
>>> + */
>>> +
>>> +#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.


Juergen