Though dev->line[] is u8 array we work with it as with u16, u24 or u32
pixels, and also pass it to memcpy() and it's better to align it to at
least 4.
Before the patch, on x86 offsetof(vivi_dev, line) was 1003 and after
patch it is 1004.
There is slight performance increase, but I think is is slight, only
because we start copying not from line[0]:
    ---- 8< ---- drivers/media/platform/vivi.c
    static void vivi_fillbuff(struct vivi_dev *dev, struct vivi_buffer *buf)
    {
            ...
            for (h = 0; h < hmax; h++)
                    memcpy(vbuf + h * wmax * dev->pixelsize,
                           dev->line + (dev->mv_count % wmax) * dev->pixelsize,
                           wmax * dev->pixelsize);
before:
    # cmdline : /home/kirr/local/perf/bin/perf record -g -a sleep 20
    #
    # Samples: 49K of event 'cycles'
    # Event count (approx.): 16799780016
    #
    # Overhead          Command         Shared Object
    # ........  ...............  ....................
    #
        27.51%             rawv  libc-2.13.so          [.] __memcpy_ssse3
        23.77%           vivi-*  [kernel.kallsyms]     [k] memcpy
         9.96%             Xorg  [unknown]             [.] 0xa76f5e12
         4.94%           vivi-*  [vivi]                [k] gen_text.constprop.6
         4.44%             rawv  [vivi]                [k] gen_twopix
         3.17%           vivi-*  [vivi]                [k] vivi_fillbuff
         2.45%             rawv  [vivi]                [k] precalculate_line
         1.20%          swapper  [kernel.kallsyms]     [k] read_hpet
    23.77%           vivi-*  [kernel.kallsyms]     [k] memcpy
                     |
                     --- memcpy
                        |
                        |--99.28%-- vivi_fillbuff
                        |          vivi_thread
                        |          kthread
                        |          ret_from_kernel_thread
                         --0.72%-- [...]
after:
    # cmdline : /home/kirr/local/perf/bin/perf record -g -a sleep 20
    #
    # Samples: 49K of event 'cycles'
    # Event count (approx.): 16475832370
    #
    # Overhead          Command           Shared Object
    # ........  ...............  ......................
    #
        29.07%             rawv  libc-2.13.so            [.] __memcpy_ssse3
        20.57%           vivi-*  [kernel.kallsyms]       [k] memcpy
        10.20%             Xorg  [unknown]               [.] 0xa7301494
         5.16%           vivi-*  [vivi]                  [k] gen_text.constprop.6
         4.43%             rawv  [vivi]                  [k] gen_twopix
         4.36%           vivi-*  [vivi]                  [k] vivi_fillbuff
         2.42%             rawv  [vivi]                  [k] precalculate_line
         1.33%          swapper  [kernel.kallsyms]       [k] read_hpet
Signed-off-by: Kirill Smelkov <kirr@mns.spb.ru>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>