> -----Original Message----- > From: KOSAKI Motohiro [mailto:kosaki.motohiro@xxxxxxxxx] > Sent: Monday, May 14, 2012 3:33 PM > To: Inki Dae > Cc: airlied@xxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx; j.glisse@xxxxxxxxx; > minchan@xxxxxxxxxx; kyungmin.park@xxxxxxxxxxx; sw0312.kim@xxxxxxxxxxx; > jy0922.shim@xxxxxxxxxxx > Subject: Re: [PATCH 2/2 v4] drm/exynos: added userptr feature. > > > + npages = buf->size >> PAGE_SHIFT; > > Why round down? usually we use round up. > The size was already rounded up by exynos_drm_gem_userptr_ioctl so this is just used to get page count. > > > + down_read(¤t->mm->mmap_sem); > > + > > + /* > > + * Basically, all the pages from get_user_pages() can not be not > only > > + * migrated by CMA but also swapped out. > > + * > > + * The migration issue. > > + * - Pages reserved by CMA for some device using DMA could be > used by > > + * kernel and if the device driver wants to use those pages > > + * while being used by kernel then the pages are copied into > > + * other ones allocated to migrate them and then finally, > > + * the device driver can use the pages for itself. > > + * Thus, migrated, the pages being accessed by DMA could be > changed > > + * to other so this situation may incur that DMA accesses any > pages > > + * it doesn't want. > > + * > > + * But the use of get_user_pages is safe from such magration > issue > > + * because all the pages from get_user_pages CAN NOT be not only > > + * migrated, but also swapped out. > > + */ > > + get_npages = get_user_pages(current, current->mm, userptr, > > + npages, write, 1, buf->pages, NULL); > > Why force=1? It is almostly core-dump specific option. Why don't you > return I know that force indicates whether to force write access even if user mapping is readonly. so we just want to use pages from get_user_pages as read/write permission. > EFAULT when the page has write permission. IOW, Why your Xorg module > don't map memory w/ PROT_WRITE? No, Xorg can map memory w/ PROT_WRITE. Couldn't the Xorg map w/ PROT_WRITE if force = 1? plz, let me know if there is my missing point. Thanks, Inki Dae > > > > + up_read(¤t->mm->mmap_sem); > > + if (get_npages != npages) > > + DRM_ERROR("failed to get user_pages.\n"); _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
