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Subject: Re: [PATCH] drm/xen-front: Remove CMA support
To:     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, jgross@suse.com, boris.ostrovsky@oracle.com,
        konrad.wilk@oracle.com,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
References: <20180417074012.21311-1-andr2000@gmail.com>
 <20180417090401.GA31310@phenom.ffwll.local>
From:   Oleksandr Andrushchenko <andr2000@gmail.com>
Message-ID: <d85e6232-6815-8ae2-4e26-cb6d508f7570@gmail.com>
Date:   Tue, 17 Apr 2018 12:08:29 +0300
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On 04/17/2018 12:04 PM, Daniel Vetter wrote:
> On Tue, Apr 17, 2018 at 10:40:12AM +0300, Oleksandr Andrushchenko wrote:
>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>
>> Even if xen-front allocates its buffers from contiguous memory
>> those are still not contiguous in PA space, e.g. the buffer is only
>> contiguous in IPA space.
>> The only use-case for this mode was if xen-front is used to allocate
>> dumb buffers which later be used by some other driver requiring
>> contiguous memory, but there is no currently such a use-case or
>> it can be worked around with xen-front.
> Please also mention the nents confusion here, and the patch that fixes it.
> Or just outright take the commit message from my patch with all the
> details:
ok, if you don't mind then I'll use your commit message entirely
>      drm/xen: Dissable CMA support
>      
>      It turns out this was only needed to paper over a bug in the CMA
>      helpers, which was addressed in
>      
>      commit 998fb1a0f478b83492220ff79583bf9ad538bdd8
>      Author: Liviu Dudau <Liviu.Dudau@arm.com>
>      Date:   Fri Nov 10 13:33:10 2017 +0000
>      
>          drm: gem_cma_helper.c: Allow importing of contiguous scatterlists with nents > 1
>      
>      Without this the following pipeline didn't work:
>      
>      domU:
>      1. xen-front allocates a non-contig buffer
>      2. creates grants out of it
>      
>      dom0:
>      3. converts the grants into a dma-buf. Since they're non-contig, the
>      scatter-list is huge.
>      4. imports it into rcar-du, which requires dma-contig memory for
>      scanout.
>      
>      -> On this given platform there's an IOMMU, so in theory this should
>      work. But in practice this failed, because of the huge number of sg
>      entries, even though the IOMMU driver mapped it all into a dma-contig
>      range.
>      
>      With a guest-contig buffer allocated in step 1, this problem doesn't
>      exist. But there's technically no reason to require guest-contig
>      memory for xen buffer sharing using grants.
>
> With the commit message improved:
>
> Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Thank you,
I'll wait for a day and apply to drm-misc-next if this is ok
>
>> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>> Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
>> ---
>>   Documentation/gpu/xen-front.rst             | 12 ----
>>   drivers/gpu/drm/xen/Kconfig                 | 13 ----
>>   drivers/gpu/drm/xen/Makefile                |  9 +--
>>   drivers/gpu/drm/xen/xen_drm_front.c         | 62 +++-------------
>>   drivers/gpu/drm/xen/xen_drm_front.h         | 42 ++---------
>>   drivers/gpu/drm/xen/xen_drm_front_gem.c     | 12 +---
>>   drivers/gpu/drm/xen/xen_drm_front_gem.h     |  3 -
>>   drivers/gpu/drm/xen/xen_drm_front_gem_cma.c | 79 ---------------------
>>   drivers/gpu/drm/xen/xen_drm_front_shbuf.c   | 22 ------
>>   drivers/gpu/drm/xen/xen_drm_front_shbuf.h   |  8 ---
>>   10 files changed, 21 insertions(+), 241 deletions(-)
>>   delete mode 100644 drivers/gpu/drm/xen/xen_drm_front_gem_cma.c
>>
>> diff --git a/Documentation/gpu/xen-front.rst b/Documentation/gpu/xen-front.rst
>> index 009d942386c5..d988da7d1983 100644
>> --- a/Documentation/gpu/xen-front.rst
>> +++ b/Documentation/gpu/xen-front.rst
>> @@ -18,18 +18,6 @@ Buffers allocated by the frontend driver
>>   .. kernel-doc:: drivers/gpu/drm/xen/xen_drm_front.h
>>      :doc: Buffers allocated by the frontend driver
>>   
>> -With GEM CMA helpers
>> -~~~~~~~~~~~~~~~~~~~~
>> -
>> -.. kernel-doc:: drivers/gpu/drm/xen/xen_drm_front.h
>> -   :doc: With GEM CMA helpers
>> -
>> -Without GEM CMA helpers
>> -~~~~~~~~~~~~~~~~~~~~~~~
>> -
>> -.. kernel-doc:: drivers/gpu/drm/xen/xen_drm_front.h
>> -   :doc: Without GEM CMA helpers
>> -
>>   Buffers allocated by the backend
>>   --------------------------------
>>   
>> diff --git a/drivers/gpu/drm/xen/Kconfig b/drivers/gpu/drm/xen/Kconfig
>> index 4f4abc91f3b6..4cca160782ab 100644
>> --- a/drivers/gpu/drm/xen/Kconfig
>> +++ b/drivers/gpu/drm/xen/Kconfig
>> @@ -15,16 +15,3 @@ config DRM_XEN_FRONTEND
>>   	help
>>   	  Choose this option if you want to enable a para-virtualized
>>   	  frontend DRM/KMS driver for Xen guest OSes.
>> -
>> -config DRM_XEN_FRONTEND_CMA
>> -	bool "Use DRM CMA to allocate dumb buffers"
>> -	depends on DRM_XEN_FRONTEND
>> -	select DRM_KMS_CMA_HELPER
>> -	select DRM_GEM_CMA_HELPER
>> -	help
>> -	  Use DRM CMA helpers to allocate display buffers.
>> -	  This is useful for the use-cases when guest driver needs to
>> -	  share or export buffers to other drivers which only expect
>> -	  contiguous buffers.
>> -	  Note: in this mode driver cannot use buffers allocated
>> -	  by the backend.
>> diff --git a/drivers/gpu/drm/xen/Makefile b/drivers/gpu/drm/xen/Makefile
>> index 352730dc6c13..712afff5ffc3 100644
>> --- a/drivers/gpu/drm/xen/Makefile
>> +++ b/drivers/gpu/drm/xen/Makefile
>> @@ -5,12 +5,7 @@ drm_xen_front-objs := xen_drm_front.o \
>>   		      xen_drm_front_conn.o \
>>   		      xen_drm_front_evtchnl.o \
>>   		      xen_drm_front_shbuf.o \
>> -		      xen_drm_front_cfg.o
>> -
>> -ifeq ($(CONFIG_DRM_XEN_FRONTEND_CMA),y)
>> -	drm_xen_front-objs += xen_drm_front_gem_cma.o
>> -else
>> -	drm_xen_front-objs += xen_drm_front_gem.o
>> -endif
>> +		      xen_drm_front_cfg.o \
>> +		      xen_drm_front_gem.o
>>   
>>   obj-$(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
>> index 4a08b77f1c9e..1b0ea9ac330e 100644
>> --- a/drivers/gpu/drm/xen/xen_drm_front.c
>> +++ b/drivers/gpu/drm/xen/xen_drm_front.c
>> @@ -12,7 +12,6 @@
>>   #include <drm/drm_atomic_helper.h>
>>   #include <drm/drm_crtc_helper.h>
>>   #include <drm/drm_gem.h>
>> -#include <drm/drm_gem_cma_helper.h>
>>   
>>   #include <linux/of_device.h>
>>   
>> @@ -167,10 +166,9 @@ int xen_drm_front_mode_set(struct xen_drm_front_drm_pipeline *pipeline,
>>   	return ret;
>>   }
>>   
>> -static int be_dbuf_create_int(struct xen_drm_front_info *front_info,
>> +int xen_drm_front_dbuf_create(struct xen_drm_front_info *front_info,
>>   			      u64 dbuf_cookie, u32 width, u32 height,
>> -			      u32 bpp, u64 size, struct page **pages,
>> -			      struct sg_table *sgt)
>> +			      u32 bpp, u64 size, struct page **pages)
>>   {
>>   	struct xen_drm_front_evtchnl *evtchnl;
>>   	struct xen_drm_front_shbuf *shbuf;
>> @@ -187,7 +185,6 @@ static int be_dbuf_create_int(struct xen_drm_front_info *front_info,
>>   	buf_cfg.xb_dev = front_info->xb_dev;
>>   	buf_cfg.pages = pages;
>>   	buf_cfg.size = size;
>> -	buf_cfg.sgt = sgt;
>>   	buf_cfg.be_alloc = front_info->cfg.be_alloc;
>>   
>>   	shbuf = xen_drm_front_shbuf_alloc(&buf_cfg);
>> @@ -237,22 +234,6 @@ static int be_dbuf_create_int(struct xen_drm_front_info *front_info,
>>   	return ret;
>>   }
>>   
>> -int xen_drm_front_dbuf_create_from_sgt(struct xen_drm_front_info *front_info,
>> -				       u64 dbuf_cookie, u32 width, u32 height,
>> -				       u32 bpp, u64 size, struct sg_table *sgt)
>> -{
>> -	return be_dbuf_create_int(front_info, dbuf_cookie, width, height,
>> -				  bpp, size, NULL, sgt);
>> -}
>> -
>> -int xen_drm_front_dbuf_create_from_pages(struct xen_drm_front_info *front_info,
>> -					 u64 dbuf_cookie, u32 width, u32 height,
>> -					 u32 bpp, u64 size, struct page **pages)
>> -{
>> -	return be_dbuf_create_int(front_info, dbuf_cookie, width, height,
>> -				  bpp, size, pages, NULL);
>> -}
>> -
>>   static int xen_drm_front_dbuf_destroy(struct xen_drm_front_info *front_info,
>>   				      u64 dbuf_cookie)
>>   {
>> @@ -434,24 +415,11 @@ static int xen_drm_drv_dumb_create(struct drm_file *filp,
>>   		goto fail;
>>   	}
>>   
>> -	/*
>> -	 * In case of CONFIG_DRM_XEN_FRONTEND_CMA gem_obj is constructed
>> -	 * via DRM CMA helpers and doesn't have ->pages allocated
>> -	 * (xendrm_gem_get_pages will return NULL), but instead can provide
>> -	 * sg table
>> -	 */
>> -	if (xen_drm_front_gem_get_pages(obj))
>> -		ret = xen_drm_front_dbuf_create_from_pages(drm_info->front_info,
>> -				xen_drm_front_dbuf_to_cookie(obj),
>> -				args->width, args->height, args->bpp,
>> -				args->size,
>> -				xen_drm_front_gem_get_pages(obj));
>> -	else
>> -		ret = xen_drm_front_dbuf_create_from_sgt(drm_info->front_info,
>> -				xen_drm_front_dbuf_to_cookie(obj),
>> -				args->width, args->height, args->bpp,
>> -				args->size,
>> -				xen_drm_front_gem_get_sg_table(obj));
>> +	ret = xen_drm_front_dbuf_create(drm_info->front_info,
>> +					xen_drm_front_dbuf_to_cookie(obj),
>> +					args->width, args->height, args->bpp,
>> +					args->size,
>> +					xen_drm_front_gem_get_pages(obj));
>>   	if (ret)
>>   		goto fail_backend;
>>   
>> @@ -523,11 +491,7 @@ static const struct file_operations xen_drm_dev_fops = {
>>   	.poll           = drm_poll,
>>   	.read           = drm_read,
>>   	.llseek         = no_llseek,
>> -#ifdef CONFIG_DRM_XEN_FRONTEND_CMA
>> -	.mmap           = drm_gem_cma_mmap,
>> -#else
>>   	.mmap           = xen_drm_front_gem_mmap,
>> -#endif
>>   };
>>   
>>   static const struct vm_operations_struct xen_drm_drv_vm_ops = {
>> @@ -547,6 +511,9 @@ static struct drm_driver xen_drm_driver = {
>>   	.gem_prime_export          = drm_gem_prime_export,
>>   	.gem_prime_import_sg_table = xen_drm_front_gem_import_sg_table,
>>   	.gem_prime_get_sg_table    = xen_drm_front_gem_get_sg_table,
>> +	.gem_prime_vmap            = xen_drm_front_gem_prime_vmap,
>> +	.gem_prime_vunmap          = xen_drm_front_gem_prime_vunmap,
>> +	.gem_prime_mmap            = xen_drm_front_gem_prime_mmap,
>>   	.dumb_create               = xen_drm_drv_dumb_create,
>>   	.fops                      = &xen_drm_dev_fops,
>>   	.name                      = "xendrm-du",
>> @@ -555,15 +522,6 @@ static struct drm_driver xen_drm_driver = {
>>   	.major                     = 1,
>>   	.minor                     = 0,
>>   
>> -#ifdef CONFIG_DRM_XEN_FRONTEND_CMA
>> -	.gem_prime_vmap            = drm_gem_cma_prime_vmap,
>> -	.gem_prime_vunmap          = drm_gem_cma_prime_vunmap,
>> -	.gem_prime_mmap            = drm_gem_cma_prime_mmap,
>> -#else
>> -	.gem_prime_vmap            = xen_drm_front_gem_prime_vmap,
>> -	.gem_prime_vunmap          = xen_drm_front_gem_prime_vunmap,
>> -	.gem_prime_mmap            = xen_drm_front_gem_prime_mmap,
>> -#endif
>>   };
>>   
>>   static int xen_drm_drv_init(struct xen_drm_front_info *front_info)
>> diff --git a/drivers/gpu/drm/xen/xen_drm_front.h b/drivers/gpu/drm/xen/xen_drm_front.h
>> index 16554b2463d8..2c2479b571ae 100644
>> --- a/drivers/gpu/drm/xen/xen_drm_front.h
>> +++ b/drivers/gpu/drm/xen/xen_drm_front.h
>> @@ -23,40 +23,14 @@
>>    *
>>    * Depending on the requirements for the para-virtualized environment, namely
>>    * requirements dictated by the accompanying DRM/(v)GPU drivers running in both
>> - * host and guest environments, number of operating modes of para-virtualized
>> - * display driver are supported:
>> - *
>> - * - display buffers can be allocated by either frontend driver or backend
>> - * - display buffers can be allocated to be contiguous in memory or not
>> - *
>> - * Note! Frontend driver itself has no dependency on contiguous memory for
>> - * its operation.
>> + * host and guest environments, display buffers can be allocated by either
>> + * frontend driver or backend.
>>    */
>>   
>>   /**
>>    * DOC: Buffers allocated by the frontend driver
>>    *
>> - * The below modes of operation are configured at compile-time via
>> - * frontend driver's kernel configuration:
>> - */
>> -
>> -/**
>> - * DOC: With GEM CMA helpers
>> - *
>> - * This use-case is useful when used with accompanying DRM/vGPU driver in
>> - * guest domain which was designed to only work with contiguous buffers,
>> - * e.g. DRM driver based on GEM CMA helpers: such drivers can only import
>> - * contiguous PRIME buffers, thus requiring frontend driver to provide
>> - * such. In order to implement this mode of operation para-virtualized
>> - * frontend driver can be configured to use GEM CMA helpers.
>> - */
>> -
>> -/**
>> - * DOC: Without GEM CMA helpers
>> - *
>> - * If accompanying drivers can cope with non-contiguous memory then, to
>> - * lower pressure on CMA subsystem of the kernel, driver can allocate
>> - * buffers from system memory.
>> + * In this mode of operation driver allocates buffers from system memory.
>>    *
>>    * Note! If used with accompanying DRM/(v)GPU drivers this mode of operation
>>    * may require IOMMU support on the platform, so accompanying DRM/vGPU
>> @@ -164,13 +138,9 @@ int xen_drm_front_mode_set(struct xen_drm_front_drm_pipeline *pipeline,
>>   			   u32 x, u32 y, u32 width, u32 height,
>>   			   u32 bpp, u64 fb_cookie);
>>   
>> -int xen_drm_front_dbuf_create_from_sgt(struct xen_drm_front_info *front_info,
>> -				       u64 dbuf_cookie, u32 width, u32 height,
>> -				       u32 bpp, u64 size, struct sg_table *sgt);
>> -
>> -int xen_drm_front_dbuf_create_from_pages(struct xen_drm_front_info *front_info,
>> -					 u64 dbuf_cookie, u32 width, u32 height,
>> -					 u32 bpp, u64 size, struct page **pages);
>> +int xen_drm_front_dbuf_create(struct xen_drm_front_info *front_info,
>> +			      u64 dbuf_cookie, u32 width, u32 height,
>> +			      u32 bpp, u64 size, struct page **pages);
>>   
>>   int xen_drm_front_fb_attach(struct xen_drm_front_info *front_info,
>>   			    u64 dbuf_cookie, u64 fb_cookie, u32 width,
>> diff --git a/drivers/gpu/drm/xen/xen_drm_front_gem.c b/drivers/gpu/drm/xen/xen_drm_front_gem.c
>> index 3b04a2269d7a..c85bfe7571cb 100644
>> --- a/drivers/gpu/drm/xen/xen_drm_front_gem.c
>> +++ b/drivers/gpu/drm/xen/xen_drm_front_gem.c
>> @@ -210,15 +210,9 @@ xen_drm_front_gem_import_sg_table(struct drm_device *dev,
>>   	if (ret < 0)
>>   		return ERR_PTR(ret);
>>   
>> -	/*
>> -	 * N.B. Although we have an API to create display buffer from sgt
>> -	 * we use pages API, because we still need those for GEM handling,
>> -	 * e.g. for mapping etc.
>> -	 */
>> -	ret = xen_drm_front_dbuf_create_from_pages(drm_info->front_info,
>> -						   xen_drm_front_dbuf_to_cookie(&xen_obj->base),
>> -						   0, 0, 0, size,
>> -						   xen_obj->pages);
>> +	ret = xen_drm_front_dbuf_create(drm_info->front_info,
>> +					xen_drm_front_dbuf_to_cookie(&xen_obj->base),
>> +					0, 0, 0, size, xen_obj->pages);
>>   	if (ret < 0)
>>   		return ERR_PTR(ret);
>>   
>> diff --git a/drivers/gpu/drm/xen/xen_drm_front_gem.h b/drivers/gpu/drm/xen/xen_drm_front_gem.h
>> index 55e531f5a763..d5ab734fdafe 100644
>> --- a/drivers/gpu/drm/xen/xen_drm_front_gem.h
>> +++ b/drivers/gpu/drm/xen/xen_drm_front_gem.h
>> @@ -27,8 +27,6 @@ struct page **xen_drm_front_gem_get_pages(struct drm_gem_object *obj);
>>   
>>   void xen_drm_front_gem_free_object_unlocked(struct drm_gem_object *gem_obj);
>>   
>> -#ifndef CONFIG_DRM_XEN_FRONTEND_CMA
>> -
>>   int xen_drm_front_gem_mmap(struct file *filp, struct vm_area_struct *vma);
>>   
>>   void *xen_drm_front_gem_prime_vmap(struct drm_gem_object *gem_obj);
>> @@ -38,6 +36,5 @@ void xen_drm_front_gem_prime_vunmap(struct drm_gem_object *gem_obj,
>>   
>>   int xen_drm_front_gem_prime_mmap(struct drm_gem_object *gem_obj,
>>   				 struct vm_area_struct *vma);
>> -#endif
>>   
>>   #endif /* __XEN_DRM_FRONT_GEM_H */
>> diff --git a/drivers/gpu/drm/xen/xen_drm_front_gem_cma.c b/drivers/gpu/drm/xen/xen_drm_front_gem_cma.c
>> deleted file mode 100644
>> index ba30a4bc2a39..000000000000
>> --- a/drivers/gpu/drm/xen/xen_drm_front_gem_cma.c
>> +++ /dev/null
>> @@ -1,79 +0,0 @@
>> -// SPDX-License-Identifier: GPL-2.0 OR MIT
>> -
>> -/*
>> - *  Xen para-virtual DRM device
>> - *
>> - * Copyright (C) 2016-2018 EPAM Systems Inc.
>> - *
>> - * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>> - */
>> -
>> -#include <drm/drmP.h>
>> -#include <drm/drm_gem.h>
>> -#include <drm/drm_fb_cma_helper.h>
>> -#include <drm/drm_gem_cma_helper.h>
>> -
>> -#include "xen_drm_front.h"
>> -#include "xen_drm_front_gem.h"
>> -
>> -struct drm_gem_object *
>> -xen_drm_front_gem_import_sg_table(struct drm_device *dev,
>> -				  struct dma_buf_attachment *attach,
>> -				  struct sg_table *sgt)
>> -{
>> -	struct xen_drm_front_drm_info *drm_info = dev->dev_private;
>> -	struct drm_gem_object *gem_obj;
>> -	struct drm_gem_cma_object *cma_obj;
>> -	int ret;
>> -
>> -	gem_obj = drm_gem_cma_prime_import_sg_table(dev, attach, sgt);
>> -	if (IS_ERR_OR_NULL(gem_obj))
>> -		return gem_obj;
>> -
>> -	cma_obj = to_drm_gem_cma_obj(gem_obj);
>> -
>> -	ret = xen_drm_front_dbuf_create_from_sgt(drm_info->front_info,
>> -						 xen_drm_front_dbuf_to_cookie(gem_obj),
>> -						 0, 0, 0, gem_obj->size,
>> -						 drm_gem_cma_prime_get_sg_table(gem_obj));
>> -	if (ret < 0)
>> -		return ERR_PTR(ret);
>> -
>> -	DRM_DEBUG("Imported CMA buffer of size %zu\n", gem_obj->size);
>> -
>> -	return gem_obj;
>> -}
>> -
>> -struct sg_table *xen_drm_front_gem_get_sg_table(struct drm_gem_object *gem_obj)
>> -{
>> -	return drm_gem_cma_prime_get_sg_table(gem_obj);
>> -}
>> -
>> -struct drm_gem_object *xen_drm_front_gem_create(struct drm_device *dev,
>> -						size_t size)
>> -{
>> -	struct xen_drm_front_drm_info *drm_info = dev->dev_private;
>> -	struct drm_gem_cma_object *cma_obj;
>> -
>> -	if (drm_info->front_info->cfg.be_alloc) {
>> -		/* This use-case is not yet supported and probably won't be */
>> -		DRM_ERROR("Backend allocated buffers and CMA helpers are not supported at the same time\n");
>> -		return ERR_PTR(-EINVAL);
>> -	}
>> -
>> -	cma_obj = drm_gem_cma_create(dev, size);
>> -	if (IS_ERR_OR_NULL(cma_obj))
>> -		return ERR_CAST(cma_obj);
>> -
>> -	return &cma_obj->base;
>> -}
>> -
>> -void xen_drm_front_gem_free_object_unlocked(struct drm_gem_object *gem_obj)
>> -{
>> -	drm_gem_cma_free_object(gem_obj);
>> -}
>> -
>> -struct page **xen_drm_front_gem_get_pages(struct drm_gem_object *gem_obj)
>> -{
>> -	return NULL;
>> -}
>> diff --git a/drivers/gpu/drm/xen/xen_drm_front_shbuf.c b/drivers/gpu/drm/xen/xen_drm_front_shbuf.c
>> index 19914dde4b3d..d5705251a0d6 100644
>> --- a/drivers/gpu/drm/xen/xen_drm_front_shbuf.c
>> +++ b/drivers/gpu/drm/xen/xen_drm_front_shbuf.c
>> @@ -89,10 +89,6 @@ void xen_drm_front_shbuf_free(struct xen_drm_front_shbuf *buf)
>>   	}
>>   	kfree(buf->grefs);
>>   	kfree(buf->directory);
>> -	if (buf->sgt) {
>> -		sg_free_table(buf->sgt);
>> -		kvfree(buf->pages);
>> -	}
>>   	kfree(buf);
>>   }
>>   
>> @@ -350,17 +346,6 @@ static int grant_references(struct xen_drm_front_shbuf *buf)
>>   
>>   static int alloc_storage(struct xen_drm_front_shbuf *buf)
>>   {
>> -	if (buf->sgt) {
>> -		buf->pages = kvmalloc_array(buf->num_pages,
>> -					    sizeof(struct page *), GFP_KERNEL);
>> -		if (!buf->pages)
>> -			return -ENOMEM;
>> -
>> -		if (drm_prime_sg_to_page_addr_arrays(buf->sgt, buf->pages,
>> -						     NULL, buf->num_pages) < 0)
>> -			return -EINVAL;
>> -	}
>> -
>>   	buf->grefs = kcalloc(buf->num_grefs, sizeof(*buf->grefs), GFP_KERNEL);
>>   	if (!buf->grefs)
>>   		return -ENOMEM;
>> @@ -396,12 +381,6 @@ xen_drm_front_shbuf_alloc(struct xen_drm_front_shbuf_cfg *cfg)
>>   	struct xen_drm_front_shbuf *buf;
>>   	int ret;
>>   
>> -	/* either pages or sgt, not both */
>> -	if (unlikely(cfg->pages && cfg->sgt)) {
>> -		DRM_ERROR("Cannot handle buffer allocation with both pages and sg table provided\n");
>> -		return NULL;
>> -	}
>> -
>>   	buf = kzalloc(sizeof(*buf), GFP_KERNEL);
>>   	if (!buf)
>>   		return NULL;
>> @@ -413,7 +392,6 @@ xen_drm_front_shbuf_alloc(struct xen_drm_front_shbuf_cfg *cfg)
>>   
>>   	buf->xb_dev = cfg->xb_dev;
>>   	buf->num_pages = DIV_ROUND_UP(cfg->size, PAGE_SIZE);
>> -	buf->sgt = cfg->sgt;
>>   	buf->pages = cfg->pages;
>>   
>>   	buf->ops->calc_num_grefs(buf);
>> diff --git a/drivers/gpu/drm/xen/xen_drm_front_shbuf.h b/drivers/gpu/drm/xen/xen_drm_front_shbuf.h
>> index 8c037fd7608b..7545c692539e 100644
>> --- a/drivers/gpu/drm/xen/xen_drm_front_shbuf.h
>> +++ b/drivers/gpu/drm/xen/xen_drm_front_shbuf.h
>> @@ -29,16 +29,9 @@ struct xen_drm_front_shbuf {
>>   	grant_ref_t *grefs;
>>   	unsigned char *directory;
>>   
>> -	/*
>> -	 * there are 2 ways to provide backing storage for this shared buffer:
>> -	 * either pages or sgt. if buffer created from sgt then we own
>> -	 * the pages and must free those ourselves on closure
>> -	 */
>>   	int num_pages;
>>   	struct page **pages;
>>   
>> -	struct sg_table *sgt;
>> -
>>   	struct xenbus_device *xb_dev;
>>   
>>   	/* these are the ops used internally depending on be_alloc mode */
>> @@ -52,7 +45,6 @@ struct xen_drm_front_shbuf_cfg {
>>   	struct xenbus_device *xb_dev;
>>   	size_t size;
>>   	struct page **pages;
>> -	struct sg_table *sgt;
>>   	bool be_alloc;
>>   };
>>   
>> -- 
>> 2.17.0
>>
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