linux-kernel - RE: [RFC PATCH 02/10] mtd: nand: omap: Always use chip->ecc.steps for BCH sector count

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Date:	Fri, 11 Jul 2014 07:43:13 +0000
From:	"Gupta, Pekon" <pekon@...com>
To:	"Quadros, Roger" <rogerq@...com>,
	"tony@...mide.com" <tony@...mide.com>,
	"computersforpeace@...il.com" <computersforpeace@...il.com>
CC:	"javier@...hile0.org" <javier@...hile0.org>,
	"ezequiel.garcia@...e-electrons.com" 
	<ezequiel.garcia@...e-electrons.com>,
	"dwmw2@...radead.org" <dwmw2@...radead.org>,
	"jg1.han@...sung.com" <jg1.han@...sung.com>,
	"Nori, Sekhar" <nsekhar@...com>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [RFC PATCH 02/10] mtd: nand: omap: Always use chip->ecc.steps
 for BCH sector count

>From: Quadros, Roger
>
>Instead of hardcoding use the pre-calculated chip->ecc.steps for
>configuring number of sectors to process with the BCH algorithm.
>
>This also avoids unnecessary access to the ECC_CONFIG register in
>omap_calculate_ecc_bch().
>
>Signed-off-by: Roger Quadros <rogerq@...com>
>---
> drivers/mtd/nand/omap2.c | 9 +++------
> 1 file changed, 3 insertions(+), 6 deletions(-)
>
>diff --git a/drivers/mtd/nand/omap2.c b/drivers/mtd/nand/omap2.c
>index 5b8739c..6f3d7cd 100644
>--- a/drivers/mtd/nand/omap2.c
>+++ b/drivers/mtd/nand/omap2.c
>@@ -1066,10 +1066,10 @@ static void __maybe_unused omap_enable_hwecc_bch(struct mtd_info
>*mtd, int mode)
> 	unsigned int ecc_size1, ecc_size0;
>
> 	/* GPMC configurations for calculating ECC */
>+	nsectors = chip->ecc.steps;
> 	switch (ecc_opt) {
> 	case OMAP_ECC_BCH4_CODE_HW_DETECTION_SW:
> 		bch_type = 0;
>-		nsectors = 1;
> 		if (mode == NAND_ECC_READ) {
> 			wr_mode	  = BCH_WRAPMODE_6;
> 			ecc_size0 = BCH_ECC_SIZE0;
>@@ -1082,7 +1082,6 @@ static void __maybe_unused omap_enable_hwecc_bch(struct mtd_info
>*mtd, int mode)
> 		break;
> 	case OMAP_ECC_BCH4_CODE_HW:
> 		bch_type = 0;
>-		nsectors = chip->ecc.steps;
> 		if (mode == NAND_ECC_READ) {
> 			wr_mode	  = BCH_WRAPMODE_1;
> 			ecc_size0 = BCH4R_ECC_SIZE0;
>@@ -1095,7 +1094,6 @@ static void __maybe_unused omap_enable_hwecc_bch(struct mtd_info
>*mtd, int mode)
> 		break;
> 	case OMAP_ECC_BCH8_CODE_HW_DETECTION_SW:
> 		bch_type = 1;
>-		nsectors = 1;
> 		if (mode == NAND_ECC_READ) {
> 			wr_mode	  = BCH_WRAPMODE_6;
> 			ecc_size0 = BCH_ECC_SIZE0;
>@@ -1108,7 +1106,6 @@ static void __maybe_unused omap_enable_hwecc_bch(struct mtd_info
>*mtd, int mode)
> 		break;
> 	case OMAP_ECC_BCH8_CODE_HW:
> 		bch_type = 1;
>-		nsectors = chip->ecc.steps;
> 		if (mode == NAND_ECC_READ) {
> 			wr_mode	  = BCH_WRAPMODE_1;
> 			ecc_size0 = BCH8R_ECC_SIZE0;
>@@ -1121,7 +1118,6 @@ static void __maybe_unused omap_enable_hwecc_bch(struct mtd_info
>*mtd, int mode)
> 		break;
> 	case OMAP_ECC_BCH16_CODE_HW:
> 		bch_type = 0x2;
>-		nsectors = chip->ecc.steps;
> 		if (mode == NAND_ECC_READ) {
> 			wr_mode	  = 0x01;
> 			ecc_size0 = 52; /* ECC bits in nibbles per sector */
>@@ -1176,6 +1172,7 @@ static int __maybe_unused omap_calculate_ecc_bch(struct mtd_info *mtd,
> {
> 	struct omap_nand_info *info = container_of(mtd, struct omap_nand_info,
> 						   mtd);
>+	struct nand_chip *chip = mtd->priv;
> 	int eccbytes	= info->nand.ecc.bytes;
> 	struct gpmc_nand_regs	*gpmc_regs = &info->reg;
> 	u8 *ecc_code;
>@@ -1183,7 +1180,7 @@ static int __maybe_unused omap_calculate_ecc_bch(struct mtd_info *mtd,
> 	u32 val;
> 	int i, j;
>
>-	nsectors = ((readl(info->reg.gpmc_ecc_config) >> 4) & 0x7) + 1;
>+	nsectors = chip->ecc.steps;

Sorry NAK.. I'm sure you are breaking something here :-)

NAND driver supports multiple ECC schemes like;
OMAP_ECC_CODE_HAM1_HW (support for legacy reasons)
OMAP_ECC_CODE_BCH4_HW_DETECTION_SW (needed for OMAP3 and AM35xx)
OMAP_ECC_CODE_BCH4_HW
OMAP_ECC_CODE_BCH8_HW
OMAP_ECC_CODE_BCH8_HW_DETECTION_SW  (needed for OMAP3 and AM35xx)
OMAP_ECC_CODE_BCH16_HW

IIRC ..
- software based ecc-schemes OMAP_ECC_CODE_BCHx_HW_DETECTION_SW
  Reads/Write in per-sector granularity. (here nsector != chip->ecc.steps)

- hardware based ecc-schemes OMAP_ECC_CODE_BCHx_HW, perform
  Reads/Write in per-page granularity (or something like this).
  Therefore you have custom implementation of 
  chip->ecc.read_page = omap_read_page_bch()
 Also if you change the configurations here, it will break the compatibility with
 u-boot, so images flashed via u-boot will stop to boot in kernel and vice-versa.

I suggest, please refrain from these tweaks for now..
All these optimizations have been tested on multiple scenario so please test
all ecc-schemes before doing anything, otherwise you will end-up in
a bad loop of breaking and fixing NAND driver :-).


with regards, pekon
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