fbdev: Put mmap for deferred I/O into drivers

The fbdev mmap function fb_mmap() unconditionally overrides the
driver's implementation if deferred I/O has been activated. This
makes it hard to implement mmap with anything but a vmalloc()'ed
software buffer. That is specifically a problem for DRM, where
video memory is maintained by a memory manager.

Leave the mmap handling to drivers and expect them to call the
helper for deferred I/O by thmeselves.

v4:
	* unlock mm_lock in fb_mmap() error path (Dan)
v3:
	* fix warning if fb_mmap is missing (kernel test robot)
v2:
	* print a helpful error message if the defio setup is
	  incorrect (Javier)
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220429100834.18898-2-tzimmermann@suse.de

drivers/gpu/drm/drm_fb_helper.c

@@ -2118,7 +2118,9 @@ static int drm_fbdev_fb_mmap(struct fb_info *info, struct vm_area_struct *vma)
 {
 	struct drm_fb_helper *fb_helper = info->par;
 
-	if (fb_helper->dev->driver->gem_prime_mmap)
+	if (drm_fbdev_use_shadow_fb(fb_helper))
+		return fb_deferred_io_mmap(info, vma);
+	else if (fb_helper->dev->driver->gem_prime_mmap)
 		return fb_helper->dev->driver->gem_prime_mmap(fb_helper->buffer->gem, vma);
 	else
 		return -ENODEV;

drivers/gpu/drm/vmwgfx/vmwgfx_fb.c

@@ -619,6 +619,7 @@ static const struct fb_ops vmw_fb_ops = {
 	.fb_imageblit = vmw_fb_imageblit,
 	.fb_pan_display = vmw_fb_pan_display,
 	.fb_blank = vmw_fb_blank,
+	.fb_mmap = fb_deferred_io_mmap,
 };
 
 int vmw_fb_init(struct vmw_private *vmw_priv)

drivers/hid/hid-picolcd_fb.c

@@ -428,6 +428,7 @@ static const struct fb_ops picolcdfb_ops = {
 	.fb_imageblit = picolcd_fb_imageblit,
 	.fb_check_var = picolcd_fb_check_var,
 	.fb_set_par   = picolcd_set_par,
+	.fb_mmap      = fb_deferred_io_mmap,
 };
 
 

drivers/staging/fbtft/fbtft-core.c

@@ -652,6 +652,7 @@ struct fb_info *fbtft_framebuffer_alloc(struct fbtft_display *display,
 	fbops->fb_imageblit =      fbtft_fb_imageblit;
 	fbops->fb_setcolreg =      fbtft_fb_setcolreg;
 	fbops->fb_blank     =      fbtft_fb_blank;
+	fbops->fb_mmap      =      fb_deferred_io_mmap;
 
 	fbdefio->delay =           HZ / fps;
 	fbdefio->sort_pagelist =   true;

drivers/video/fbdev/broadsheetfb.c

@@ -1055,6 +1055,7 @@ static const struct fb_ops broadsheetfb_ops = {
 	.fb_fillrect	= broadsheetfb_fillrect,
 	.fb_copyarea	= broadsheetfb_copyarea,
 	.fb_imageblit	= broadsheetfb_imageblit,
+	.fb_mmap	= fb_deferred_io_mmap,
 };
 
 static struct fb_deferred_io broadsheetfb_defio = {

drivers/video/fbdev/core/fb_defio.c

@@ -181,6 +181,7 @@ int fb_deferred_io_mmap(struct fb_info *info, struct vm_area_struct *vma)
 	vma->vm_private_data = info;
 	return 0;
 }
+EXPORT_SYMBOL_GPL(fb_deferred_io_mmap);
 
 /* workqueue callback */
 static void fb_deferred_io_work(struct work_struct *work)

drivers/video/fbdev/core/fbmem.c

@@ -1334,7 +1334,6 @@ static int
 fb_mmap(struct file *file, struct vm_area_struct * vma)
 {
 	struct fb_info *info = file_fb_info(file);
-	int (*fb_mmap_fn)(struct fb_info *info, struct vm_area_struct *vma);
 	unsigned long mmio_pgoff;
 	unsigned long start;
 	u32 len;
@@ -1343,14 +1342,7 @@ fb_mmap(struct file *file, struct vm_area_struct * vma)
 		return -ENODEV;
 	mutex_lock(&info->mm_lock);
 
-	fb_mmap_fn = info->fbops->fb_mmap;
-
-#if IS_ENABLED(CONFIG_FB_DEFERRED_IO)
-	if (info->fbdefio)
-		fb_mmap_fn = fb_deferred_io_mmap;
-#endif
-
-	if (fb_mmap_fn) {
+	if (info->fbops->fb_mmap) {
 		int res;
 
 		/*
@@ -1358,9 +1350,19 @@ fb_mmap(struct file *file, struct vm_area_struct * vma)
 		 * SME protection is removed ahead of the call
 		 */
 		vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
-		res = fb_mmap_fn(info, vma);
+		res = info->fbops->fb_mmap(info, vma);
 		mutex_unlock(&info->mm_lock);
 		return res;
+#if IS_ENABLED(CONFIG_FB_DEFERRED_IO)
+	} else if (info->fbdefio) {
+		/*
+		 * FB deferred I/O wants you to handle mmap in your drivers. At a
+		 * minimum, point struct fb_ops.fb_mmap to fb_deferred_io_mmap().
+		 */
+		dev_warn_once(info->dev, "fbdev mmap not set up for deferred I/O.\n");
+		mutex_unlock(&info->mm_lock);
+		return -ENODEV;
+#endif
 	}
 
 	/*

drivers/video/fbdev/hecubafb.c

@@ -204,6 +204,7 @@ static const struct fb_ops hecubafb_ops = {
 	.fb_fillrect	= hecubafb_fillrect,
 	.fb_copyarea	= hecubafb_copyarea,
 	.fb_imageblit	= hecubafb_imageblit,
+	.fb_mmap	= fb_deferred_io_mmap,
 };
 
 static struct fb_deferred_io hecubafb_defio = {

drivers/video/fbdev/hyperv_fb.c

@@ -909,6 +909,7 @@ static const struct fb_ops hvfb_ops = {
 	.fb_copyarea = hvfb_cfb_copyarea,
 	.fb_imageblit = hvfb_cfb_imageblit,
 	.fb_blank = hvfb_blank,
+	.fb_mmap = fb_deferred_io_mmap,
 };
 
 

drivers/video/fbdev/metronomefb.c

@@ -564,6 +564,7 @@ static const struct fb_ops metronomefb_ops = {
 	.fb_fillrect	= metronomefb_fillrect,
 	.fb_copyarea	= metronomefb_copyarea,
 	.fb_imageblit	= metronomefb_imageblit,
+	.fb_mmap	= fb_deferred_io_mmap,
 };
 
 static struct fb_deferred_io metronomefb_defio = {

drivers/video/fbdev/sh_mobile_lcdcfb.c

@@ -1480,6 +1480,9 @@ sh_mobile_lcdc_overlay_mmap(struct fb_info *info, struct vm_area_struct *vma)
 {
 	struct sh_mobile_lcdc_overlay *ovl = info->par;
 
+	if (info->fbdefio)
+		return fb_deferred_io_mmap(info, vma);
+
 	return dma_mmap_coherent(ovl->channel->lcdc->dev, vma, ovl->fb_mem,
 				 ovl->dma_handle, ovl->fb_size);
 }
@@ -1954,6 +1957,9 @@ sh_mobile_lcdc_mmap(struct fb_info *info, struct vm_area_struct *vma)
 {
 	struct sh_mobile_lcdc_chan *ch = info->par;
 
+	if (info->fbdefio)
+		return fb_deferred_io_mmap(info, vma);
+
 	return dma_mmap_coherent(ch->lcdc->dev, vma, ch->fb_mem,
 				 ch->dma_handle, ch->fb_size);
 }

drivers/video/fbdev/smscufx.c

@@ -779,6 +779,9 @@ static int ufx_ops_mmap(struct fb_info *info, struct vm_area_struct *vma)
 	unsigned long offset = vma->vm_pgoff << PAGE_SHIFT;
 	unsigned long page, pos;
 
+	if (info->fbdefio)
+		return fb_deferred_io_mmap(info, vma);
+
 	if (vma->vm_pgoff > (~0UL >> PAGE_SHIFT))
 		return -EINVAL;
 	if (size > info->fix.smem_len)

drivers/video/fbdev/ssd1307fb.c

@@ -368,6 +368,7 @@ static const struct fb_ops ssd1307fb_ops = {
 	.fb_fillrect	= ssd1307fb_fillrect,
 	.fb_copyarea	= ssd1307fb_copyarea,
 	.fb_imageblit	= ssd1307fb_imageblit,
+	.fb_mmap	= fb_deferred_io_mmap,
 };
 
 static void ssd1307fb_deferred_io(struct fb_info *info,

drivers/video/fbdev/udlfb.c

@@ -326,6 +326,9 @@ static int dlfb_ops_mmap(struct fb_info *info, struct vm_area_struct *vma)
 	unsigned long offset = vma->vm_pgoff << PAGE_SHIFT;
 	unsigned long page, pos;
 
+	if (info->fbdefio)
+		return fb_deferred_io_mmap(info, vma);
+
 	if (vma->vm_pgoff > (~0UL >> PAGE_SHIFT))
 		return -EINVAL;
 	if (size > info->fix.smem_len)

drivers/video/fbdev/xen-fbfront.c

@@ -338,6 +338,7 @@ static const struct fb_ops xenfb_fb_ops = {
 	.fb_imageblit	= xenfb_imageblit,
 	.fb_check_var	= xenfb_check_var,
 	.fb_set_par     = xenfb_set_par,
+	.fb_mmap	= fb_deferred_io_mmap,
 };
 
 static irqreturn_t xenfb_event_handler(int rq, void *dev_id)