• Inki Dae's avatar
    drm/exynos: add userptr feature for g2d module · 2a3098ff
    Inki Dae authored
    This patch adds userptr feautre for G2D module.
    
    The userptr means user space address allocated by malloc().
    And the purpose of this feature is to make G2D's dma able
    to access the user space region.
    
    To user this feature, user should flag G2D_BUF_USRPTR to
    offset variable of struct drm_exynos_g2d_cmd and fill
    struct drm_exynos_g2d_userptr with user space address
    and size for it and then should set a pointer to
    drm_exynos_g2d_userptr object to data variable of struct
    drm_exynos_g2d_cmd. The last bit of offset variable is used
    to check if the cmdlist's buffer type is userptr or not.
    If userptr, the g2d driver gets user space address and size
    and then gets pages through get_user_pages().
    (another case is counted as gem handle)
    
    Below is sample codes:
    
    static void set_cmd(struct drm_exynos_g2d_cmd *cmd,
    		unsigned long offset, unsigned long data)
    {
    	cmd->offset = offset;
    	cmd->data = data;
    }
    
    static int solid_fill_test(int x, int y, unsigned long userptr)
    {
    	struct drm_exynos_g2d_cmd cmd_gem[5];
    	struct drm_exynos_g2d_userptr g2d_userptr;
    	unsigned int gem_nr = 0;
    	...
    
    	g2d_userptr.userptr = userptr;
    	g2d_userptr.size = x * y * 4;
    
    	set_cmd(&cmd_gem[gem_nr++], DST_BASE_ADDR_REG |
    					G2D_BUF_USERPTR,
    			(unsigned long)&g2d_userptr);
    	...
    }
    
    int main(int argc, char **argv)
    {
    	unsigned long addr;
    	...
    
    	addr = malloc(x * y * 4);
    	...
    
    	solid_fill_test(x, y, addr);
    	...
    }
    
    And next, the pages are mapped with iommu table and the device
    address is set to cmdlist so that G2D's dma can access it.
    As you may know, the pages from get_user_pages() are pinned.
    In other words, they CAN NOT be migrated and also swapped out.
    So the dma access would be safe.
    
    But the use of userptr feature has performance overhead so
    this patch also has memory pool to the userptr feature.
    Please, assume that user sends cmdlist filled with userptr
    and size every time to g2d driver, and the get_user_pages
    funcion will be called every time.
    
    The memory pool has maximum 64MB size and the userptr that
    user had ever sent, is holded in the memory pool.
    This meaning is that if the userptr from user is same as one
    in the memory pool, device address to the userptr in the memory
    pool is set to cmdlist.
    
    And last, the pages from get_user_pages() will be freed once
    user calls free() and the dma access is completed. Actually,
    get_user_pages() takes 2 reference counts if the user process
    has never accessed user region allocated by malloc(). Then, if
    the user calls free(), the page reference count becomes 1 and
    becomes 0 with put_page() call. And the reverse holds as well.
    This means how the pages backed are used by dma and freed.
    
    This patch is based on "drm/exynos: add iommu support for g2d",
    	https://patchwork.kernel.org/patch/1629481/Signed-off-by: default avatarInki Dae <inki.dae@samsung.com>
    Signed-off-by: default avatarKyungmin Park <kyungmin.park@samsung.com>
    2a3098ff
exynos_drm_drv.h 11.7 KB