video: sh_mobile_lcdcfb: Don't attempt to map zero-length scatterlists.

[platform/adaptation/renesas_rcar/renesas_kernel.git] / drivers / video / sh_mobile_lcdcfb.c

diff --git a/drivers/video/sh_mobile_lcdcfb.c b/drivers/video/sh_mobile_lcdcfb.c
index 3ad5157..b4b5de9 100644 (file)
--- a/drivers/video/sh_mobile_lcdcfb.c
+++ b/drivers/video/sh_mobile_lcdcfb.c
@@ -281,18 +281,34 @@ static void sh_mobile_lcdc_deferred_io(struct fb_info *info,
                                       struct list_head *pagelist)
 {
        struct sh_mobile_lcdc_chan *ch = info->par;
-       unsigned int nr_pages;
 
        /* enable clocks before accessing hardware */
        sh_mobile_lcdc_clk_on(ch->lcdc);
 
-       nr_pages = sh_mobile_lcdc_sginit(info, pagelist);
-       dma_map_sg(info->dev, ch->sglist, nr_pages, DMA_TO_DEVICE);
-
-       /* trigger panel update */
-       lcdc_write_chan(ch, LDSM2R, 1);
-
-       dma_unmap_sg(info->dev, ch->sglist, nr_pages, DMA_TO_DEVICE);
+       /*
+        * It's possible to get here without anything on the pagelist via
+        * sh_mobile_lcdc_deferred_io_touch() or via a userspace fsync()
+        * invocation. In the former case, the acceleration routines are
+        * stepped in to when using the framebuffer console causing the
+        * workqueue to be scheduled without any dirty pages on the list.
+        *
+        * Despite this, a panel update is still needed given that the
+        * acceleration routines have their own methods for writing in
+        * that still need to be updated.
+        *
+        * The fsync() and empty pagelist case could be optimized for,
+        * but we don't bother, as any application exhibiting such
+        * behaviour is fundamentally broken anyways.
+        */
+       if (!list_empty(pagelist)) {
+               unsigned int nr_pages = sh_mobile_lcdc_sginit(info, pagelist);
+
+               /* trigger panel update */
+               dma_map_sg(info->dev, ch->sglist, nr_pages, DMA_TO_DEVICE);
+               lcdc_write_chan(ch, LDSM2R, 1);
+               dma_unmap_sg(info->dev, ch->sglist, nr_pages, DMA_TO_DEVICE);
+       } else
+               lcdc_write_chan(ch, LDSM2R, 1);
 }
 
 static void sh_mobile_lcdc_deferred_io_touch(struct fb_info *info)