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Subject: Re: [PATCH 1/9] drm/xen-front: Introduce Xen para-virtualized
 frontend driver
To:     Juergen Gross <jgross@suse.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>
From:   Oleksandr Andrushchenko <andr2000@gmail.com>
Message-ID: <91386840-c34a-31a4-2bb3-14a27ececa9c@gmail.com>
Date:   Wed, 21 Feb 2018 10:47:40 +0200
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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
>
> Juergen
Thank you,
Oleksandr