As per DW MobileStorage databook "each descriptor can transfer up to 4kB
of data in chained mode", moreover buffer size that is put in "des1" is
limited to 13 bits, i.e. for example on attempt to
IDMAC_SET_BUFFER1_SIZE(desc, 8192) size value that's effectively written
will be 0.

On the platform with 8kB PAGE_SIZE I see dw_mmc gets data blocks in
SG-list of 8kB size and that leads to unpredictable behavior of the
SD/MMC controller.

In particular on write to FAT partition of SD-card the controller will
stuck in the middle of DMA transaction.

Solution to the problem is simple - we need to pass large (> 4kB) data
buffers to the controller via multiple descriptors. And that's what
that change does.

What's interesting I did try original driver on same platform but
configured with 4kB PAGE_SIZE and may confirm that data blocks passed
in SG-list to dw_mmc never exeed 4kB limit - that explains why nobody
ever faced a problem I did.
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Seungwon Jeon <tgih.jun@samsung.com>
Cc: Jaehoon Chung <jh80.chung@samsung.com>
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: arc-linux-dev@synopsys.com
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>