Re: [PATCH 18/21] udlfb: allow reallocating the framebuffer

[kbuild test robot <lkp@intel.com>]

Hi Mikulas,

I love your patch! Perhaps something to improve:

[auto build test WARNING on drm/drm-next]
[also build test WARNING on v4.17-rc7 next-20180601]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Mikulas-Patocka/USB-DisplayLink-patches/20180603-233013
base:   git://people.freedesktop.org/~airlied/linux.git drm-next
reproduce:
        # apt-get install sparse
        make ARCH=x86_64 allmodconfig
        make C=1 CF=-D__CHECK_ENDIAN__


sparse warnings: (new ones prefixed by >>)


vim +1198 drivers/video/fbdev/udlfb.c

  1171	
  1172	/*
  1173	 * Assumes &info->lock held by caller
  1174	 * Assumes no active clients have framebuffer open
  1175	 */
  1176	static int dlfb_realloc_framebuffer(struct dlfb_data *dlfb, struct fb_info *info, u32 new_len)
  1177	{
  1178		u32 old_len = info->fix.smem_len;
> 1179		unsigned char *old_fb = info->screen_base;
  1180		unsigned char *new_fb;
  1181		unsigned char *new_back = NULL;
  1182	
  1183		new_len = PAGE_ALIGN(new_len);
  1184	
  1185		if (new_len > old_len) {
  1186			/*
  1187			 * Alloc system memory for virtual framebuffer
  1188			 */
  1189			new_fb = vmalloc(new_len);
  1190			if (!new_fb) {
  1191				dev_err(info->dev, "Virtual framebuffer alloc failed\n");
  1192				return -ENOMEM;
  1193			}
  1194			memset(new_fb, 0xff, new_len);
  1195	
  1196			if (info->screen_base) {
  1197				memcpy(new_fb, old_fb, old_len);
> 1198				dlfb_deferred_vfree(dlfb, info->screen_base);
  1199			}
  1200	
  1201			info->screen_base = new_fb;
  1202			info->fix.smem_len = new_len;
  1203			info->fix.smem_start = (unsigned long) new_fb;
  1204			info->flags = udlfb_info_flags;
  1205	
  1206			/*
  1207			 * Second framebuffer copy to mirror the framebuffer state
  1208			 * on the physical USB device. We can function without this.
  1209			 * But with imperfect damage info we may send pixels over USB
  1210			 * that were, in fact, unchanged - wasting limited USB bandwidth
  1211			 */
  1212			if (shadow)
  1213				new_back = vzalloc(new_len);
  1214			if (!new_back)
  1215				dev_info(info->dev,
  1216					 "No shadow/backing buffer allocated\n");
  1217			else {
  1218				dlfb_deferred_vfree(dlfb, dlfb->backing_buffer);
  1219				dlfb->backing_buffer = new_back;
  1220			}
  1221		}
  1222		return 0;
  1223	}
  1224	

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