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Commit e2dc4c4b authored by Sujit Reddy Thumma's avatar Sujit Reddy Thumma
Browse files

mtd: msm_qpic_nand: Support for partial page read 



MTD core layer can request the chip drivers to read data from any
offset unaligned with NAND page and any length less the NAND page
size. The controller does not support partial page read. So instead
of returning not supported error simulate the behavior using bounce
buffers.

Change-Id: I0fc22fa039fe7247822bd8c89ce8de5d7349ace6
Signed-off-by: default avatarSujit Reddy Thumma <sthumma@codeaurora.org>
parent 76ccdc74

drivers/mtd/devices/msm_qpic_nand.c

+76 −1
Original line number Diff line number Diff line
@@ -1748,6 +1748,75 @@ validate_mtd_params_failed: 
	return err;

}



/**

 * msm_nand_read_partial_page() - read partial page

 * @mtd: pointer to mtd info

 * @from: start address of the page

 * @ops: pointer to mtd_oob_ops

 *

 * Reads a page into a bounce buffer and copies the required

 * number of bytes to actual buffer. The pages that are aligned

 * do not use bounce buffer.

 */

static int msm_nand_read_partial_page(struct mtd_info *mtd,

		loff_t from, struct mtd_oob_ops *ops)

{

	int err = 0;

	unsigned char *actual_buf;

	unsigned char *bounce_buf;

	loff_t aligned_from;

	loff_t offset;

	size_t len;

	size_t actual_len;



	actual_len = ops->len;

	actual_buf = ops->datbuf;



	bounce_buf = kmalloc(mtd->writesize, GFP_KERNEL);

	if (!bounce_buf) {

		pr_err("%s: could not allocate memory\n", __func__);

		err = -ENOMEM;

		goto out;

	}



	/* Get start address of page to read from */

	ops->len = mtd->writesize;

	offset = from & (mtd->writesize - 1);

	aligned_from = from - offset;



	for (;;) {

		bool no_copy = false;



		len = mtd->writesize - offset;

		if (len > actual_len)

			len = actual_len;



		if (offset == 0 && len == mtd->writesize)

			no_copy = true;



		ops->datbuf = no_copy ? actual_buf : bounce_buf;

		err = msm_nand_read_oob(mtd, aligned_from, ops);

		if (err < 0)

			break;



		if (!no_copy)

			memcpy(actual_buf, bounce_buf + offset, len);



		actual_len -= len;

		ops->retlen += len;

		if (actual_len == 0)

			break;



		actual_buf += len;

		offset = 0;

		aligned_from += mtd->writesize;

	}



	kfree(bounce_buf);

out:

	return err;

}



/*

 * Function that gets called from upper layers such as MTD/YAFFS2 to read a

 * page with only main data.
@@ -1764,7 +1833,13 @@ static int msm_nand_read(struct mtd_info *mtd, loff_t from, size_t len, 
	ops.ooblen = 0;

	ops.datbuf = buf;

	ops.oobbuf = NULL;



	if (!(from & (mtd->writesize - 1)) && !(len % mtd->writesize))

		/* read pages on page boundary */

		ret = msm_nand_read_oob(mtd, from, &ops);

	else

		ret = msm_nand_read_partial_page(mtd, from, &ops);



	*retlen = ops.retlen;

	return ret;

}