mtd: rawnand: denali: refactor raw page accessors

The Denali IP adopts the syndrome page layout (payload and ECC are
interleaved). The *_page_raw() and *_oob() callbacks are complicated
because they must hide the underlying layout used by the hardware,
and always return contiguous in-band and out-of-band data.

The Denali IP cannot reuse nand_{read,write}_page_raw_syndrome()
in nand_base.c because its hardware ECC engine skips some of first
bytes in OOB. That is why this driver implements specially-crafted
*_page_raw() and *_oob() hooks.

Currently, similar code is duplicated to reorganize the data layout.
For example, denali_read_page_raw() and denali_write_page_raw() look
almost the same. The complexity is partly due to the DMA transfer
used for better performance of *_page_raw() accessors.

On second thought, we do not need to care about their performance
because MTD_OPS_RAW is rarely used.

Let's focus on code cleanups rather than the performance. This commit
removes the internal buffer for DMA, and factors out as much code as
possible.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

drivers/mtd/nand/raw/denali.h

@@ -303,7 +303,6 @@ struct denali_nand_info {
 	u32 irq_mask;			/* interrupts we are waiting for */
 	u32 irq_status;			/* interrupts that have happened */
 	int irq;
-	void *buf;			/* for syndrome layout conversion */
 	int dma_avail;			/* can support DMA? */
 	int devs_per_cs;		/* devices connected in parallel */
 	int oob_skip_bytes;		/* number of bytes reserved for BBM */