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SubjectRe: [PATCH] drm/xen-front: Make shmem backed display buffer coherent
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On 12/13/18 5:48 PM, Daniel Vetter wrote:
> On Thu, Dec 13, 2018 at 12:17:54PM +0200, Oleksandr Andrushchenko wrote:
>> Daniel, could you please comment?
> Cross-revieweing someone else's stuff would scale better,
fair enough
> I don't think
> I'll get around to anything before next year.

I put you on CC explicitly because you had comments on other patch [1]

and this one tries to solve the issue raised (I tried to figure out

at [2] if this is the way to go, but it seems I have no alternative here).

While at it [3] (I hope) addresses your comments and the series just

needs your single ack/nack to get in: all the rest ack/r-b are already

there. Do you mind looking at it?

> -Daniel

Thank you very much for your time,

Oleksandr

>> Thank you
>>
>> On 11/27/18 12:32 PM, Oleksandr Andrushchenko wrote:
>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>>
>>> When GEM backing storage is allocated with drm_gem_get_pages
>>> the backing pages may be cached, thus making it possible that
>>> the backend sees only partial content of the buffer which may
>>> lead to screen artifacts. Make sure that the frontend's
>>> memory is coherent and the backend always sees correct display
>>> buffer content.
>>>
>>> Fixes: c575b7eeb89f ("drm/xen-front: Add support for Xen PV display frontend")
>>>
>>> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>>> ---
>>> drivers/gpu/drm/xen/xen_drm_front_gem.c | 62 +++++++++++++++++++------
>>> 1 file changed, 48 insertions(+), 14 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/xen/xen_drm_front_gem.c b/drivers/gpu/drm/xen/xen_drm_front_gem.c
>>> index 47ff019d3aef..c592735e49d2 100644
>>> --- a/drivers/gpu/drm/xen/xen_drm_front_gem.c
>>> +++ b/drivers/gpu/drm/xen/xen_drm_front_gem.c
>>> @@ -33,8 +33,11 @@ struct xen_gem_object {
>>> /* set for buffers allocated by the backend */
>>> bool be_alloc;
>>> - /* this is for imported PRIME buffer */
>>> - struct sg_table *sgt_imported;
>>> + /*
>>> + * this is for imported PRIME buffer or the one allocated via
>>> + * drm_gem_get_pages.
>>> + */
>>> + struct sg_table *sgt;
>>> };
>>> static inline struct xen_gem_object *
>>> @@ -77,10 +80,21 @@ static struct xen_gem_object *gem_create_obj(struct drm_device *dev,
>>> return xen_obj;
>>> }
>>> +struct sg_table *xen_drm_front_gem_get_sg_table(struct drm_gem_object *gem_obj)
>>> +{
>>> + struct xen_gem_object *xen_obj = to_xen_gem_obj(gem_obj);
>>> +
>>> + if (!xen_obj->pages)
>>> + return ERR_PTR(-ENOMEM);
>>> +
>>> + return drm_prime_pages_to_sg(xen_obj->pages, xen_obj->num_pages);
>>> +}
>>> +
>>> static struct xen_gem_object *gem_create(struct drm_device *dev, size_t size)
>>> {
>>> struct xen_drm_front_drm_info *drm_info = dev->dev_private;
>>> struct xen_gem_object *xen_obj;
>>> + struct address_space *mapping;
>>> int ret;
>>> size = round_up(size, PAGE_SIZE);
>>> @@ -113,10 +127,14 @@ static struct xen_gem_object *gem_create(struct drm_device *dev, size_t size)
>>> xen_obj->be_alloc = true;
>>> return xen_obj;
>>> }
>>> +
>>> /*
>>> * need to allocate backing pages now, so we can share those
>>> * with the backend
>>> */
>>> + mapping = xen_obj->base.filp->f_mapping;
>>> + mapping_set_gfp_mask(mapping, GFP_USER | __GFP_DMA32);
>>> +
>>> xen_obj->num_pages = DIV_ROUND_UP(size, PAGE_SIZE);
>>> xen_obj->pages = drm_gem_get_pages(&xen_obj->base);
>>> if (IS_ERR_OR_NULL(xen_obj->pages)) {
>>> @@ -125,8 +143,27 @@ static struct xen_gem_object *gem_create(struct drm_device *dev, size_t size)
>>> goto fail;
>>> }
>>> + xen_obj->sgt = xen_drm_front_gem_get_sg_table(&xen_obj->base);
>>> + if (IS_ERR_OR_NULL(xen_obj->sgt)){
>>> + ret = PTR_ERR(xen_obj->sgt);
>>> + xen_obj->sgt = NULL;
>>> + goto fail_put_pages;
>>> + }
>>> +
>>> + if (!dma_map_sg(dev->dev, xen_obj->sgt->sgl, xen_obj->sgt->nents,
>>> + DMA_BIDIRECTIONAL)) {
>>> + ret = -EFAULT;
>>> + goto fail_free_sgt;
>>> + }
>>> +
>>> return xen_obj;
>>> +fail_free_sgt:
>>> + sg_free_table(xen_obj->sgt);
>>> + xen_obj->sgt = NULL;
>>> +fail_put_pages:
>>> + drm_gem_put_pages(&xen_obj->base, xen_obj->pages, true, false);
>>> + xen_obj->pages = NULL;
>>> fail:
>>> DRM_ERROR("Failed to allocate buffer with size %zu\n", size);
>>> return ERR_PTR(ret);
>>> @@ -149,7 +186,7 @@ void xen_drm_front_gem_free_object_unlocked(struct drm_gem_object *gem_obj)
>>> struct xen_gem_object *xen_obj = to_xen_gem_obj(gem_obj);
>>> if (xen_obj->base.import_attach) {
>>> - drm_prime_gem_destroy(&xen_obj->base, xen_obj->sgt_imported);
>>> + drm_prime_gem_destroy(&xen_obj->base, xen_obj->sgt);
>>> gem_free_pages_array(xen_obj);
>>> } else {
>>> if (xen_obj->pages) {
>>> @@ -158,6 +195,13 @@ void xen_drm_front_gem_free_object_unlocked(struct drm_gem_object *gem_obj)
>>> xen_obj->pages);
>>> gem_free_pages_array(xen_obj);
>>> } else {
>>> + if (xen_obj->sgt) {
>>> + dma_unmap_sg(xen_obj->base.dev->dev,
>>> + xen_obj->sgt->sgl,
>>> + xen_obj->sgt->nents,
>>> + DMA_BIDIRECTIONAL);
>>> + sg_free_table(xen_obj->sgt);
>>> + }
>>> drm_gem_put_pages(&xen_obj->base,
>>> xen_obj->pages, true, false);
>>> }
>>> @@ -174,16 +218,6 @@ struct page **xen_drm_front_gem_get_pages(struct drm_gem_object *gem_obj)
>>> return xen_obj->pages;
>>> }
>>> -struct sg_table *xen_drm_front_gem_get_sg_table(struct drm_gem_object *gem_obj)
>>> -{
>>> - struct xen_gem_object *xen_obj = to_xen_gem_obj(gem_obj);
>>> -
>>> - if (!xen_obj->pages)
>>> - return ERR_PTR(-ENOMEM);
>>> -
>>> - return drm_prime_pages_to_sg(xen_obj->pages, xen_obj->num_pages);
>>> -}
>>> -
>>> struct drm_gem_object *
>>> xen_drm_front_gem_import_sg_table(struct drm_device *dev,
>>> struct dma_buf_attachment *attach,
>>> @@ -203,7 +237,7 @@ xen_drm_front_gem_import_sg_table(struct drm_device *dev,
>>> if (ret < 0)
>>> return ERR_PTR(ret);
>>> - xen_obj->sgt_imported = sgt;
>>> + xen_obj->sgt = sgt;
>>> ret = drm_prime_sg_to_page_addr_arrays(sgt, xen_obj->pages,
>>> NULL, xen_obj->num_pages);
>> _______________________________________________
>> dri-devel mailing list
>> dri-devel@lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/dri-devel

[1] https://patchwork.kernel.org/patch/10693787/

[2] https://lists.xen.org/archives/html/xen-devel/2018-11/msg02882.html

[3] https://patchwork.kernel.org/patch/10705853/


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