Re: [PATCH 2/4] mtd: devices: elm: Add support for ELM error correction

[Peter Meerwald <pmeerw@pmeerw.net>]

some minor nitpicks below

> Platforms containing the ELM module can be used to correct errors
> reported by BCH 4, 8 & 16 bit ECC scheme. For now only 4 & 8 bit
> support is added.
> 
> Signed-off-by: Philip, Avinash <avinashphilip@ti.com>
> Cc: Grant Likely <grant.likely@secretlab.ca>
> Cc: Rob Herring <rob.herring@calxeda.com>
> Cc: Rob Landley <rob@landley.net>
> ---
> :000000 100644 0000000... b88ee83... A	Documentation/devicetree/bindings/mtd/elm.txt
> :100644 100644 395733a... 0f6a94b... M	drivers/mtd/devices/Makefile
> :000000 100644 0000000... 802b572... A	drivers/mtd/devices/elm.c
> :000000 100644 0000000... eb53163... A	include/linux/platform_data/elm.h
>  Documentation/devicetree/bindings/mtd/elm.txt |   18 +
>  drivers/mtd/devices/Makefile                  |    4 +-
>  drivers/mtd/devices/elm.c                     |  440 +++++++++++++++++++++++++
>  include/linux/platform_data/elm.h             |   60 ++++
>  4 files changed, 521 insertions(+), 1 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/mtd/elm.txt b/Documentation/devicetree/bindings/mtd/elm.txt
> new file mode 100644
> index 0000000..b88ee83
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/mtd/elm.txt
> @@ -0,0 +1,18 @@
> +Error location module
> +
> +Required properties:
> +- compatible: Must be "ti,elm"
> +- reg: physical base address and size of the registers map.
> +- interrupts: Interrupt number for the elm.
> +- interrupt-parent: The parent interrupt controller
> +
> +Optional properties:
> +- ti,hwmods: Name of the hwmod associated to the elm
> +
> +Example:
> +elm: elm@0 {
> +	compatible	= "ti,elm";
> +	reg = <0x48080000 0x2000>;
> +	interrupt-parent = <&intc>;
> +	interrupts = <4>;
> +};
> diff --git a/drivers/mtd/devices/Makefile b/drivers/mtd/devices/Makefile
> index 395733a..0f6a94b 100644
> --- a/drivers/mtd/devices/Makefile
> +++ b/drivers/mtd/devices/Makefile
> @@ -17,8 +17,10 @@ obj-$(CONFIG_MTD_LART)		+= lart.o
>  obj-$(CONFIG_MTD_BLOCK2MTD)	+= block2mtd.o
>  obj-$(CONFIG_MTD_DATAFLASH)	+= mtd_dataflash.o
>  obj-$(CONFIG_MTD_M25P80)	+= m25p80.o
> +obj-$(CONFIG_MTD_NAND_OMAP2)	+= elm.o
>  obj-$(CONFIG_MTD_SPEAR_SMI)	+= spear_smi.o
>  obj-$(CONFIG_MTD_SST25L)	+= sst25l.o
>  obj-$(CONFIG_MTD_BCM47XXSFLASH)	+= bcm47xxsflash.o
>  
> -CFLAGS_docg3.o			+= -I$(src)
> \ No newline at end of file
> +
> +CFLAGS_docg3.o			+= -I$(src)
> diff --git a/drivers/mtd/devices/elm.c b/drivers/mtd/devices/elm.c
> new file mode 100644
> index 0000000..802b572
> --- /dev/null
> +++ b/drivers/mtd/devices/elm.c
> @@ -0,0 +1,440 @@
> +/*
> + * Error Location Module
> + *
> + * Copyright (C) 2012 Texas Instruments Incorporated - http://www.ti.com/
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + */
> +
> +#include <linux/platform_device.h>
> +#include <linux/module.h>
> +#include <linux/interrupt.h>
> +#include <linux/io.h>
> +#include <linux/of.h>
> +#include <linux/pm_runtime.h>
> +#include <linux/platform_data/elm.h>
> +
> +#define ELM_IRQSTATUS			0x018
> +#define ELM_IRQENABLE			0x01c
> +#define ELM_LOCATION_CONFIG		0x020
> +#define ELM_PAGE_CTRL			0x080
> +#define ELM_SYNDROME_FRAGMENT_0		0x400
> +#define ELM_SYNDROME_FRAGMENT_6		0x418
> +#define ELM_LOCATION_STATUS		0x800
> +#define ELM_ERROR_LOCATION_0		0x880
> +
> +/* ELM Interrupt Status Register */
> +#define INTR_STATUS_PAGE_VALID		BIT(8)
> +
> +/* ELM Interrupt Enable Register */
> +#define INTR_EN_PAGE_MASK		BIT(8)
> +
> +/* ELM Location Configuration Register */
> +#define ECC_BCH_LEVEL_MASK		0x3
> +
> +/* ELM syndrome */
> +#define ELM_SYNDROME_VALID		BIT(16)
> +
> +/* ELM_LOCATION_STATUS Register */
> +#define ECC_CORRECTABLE_MASK		BIT(8)
> +#define ECC_NB_ERRORS_MASK		0x1f
> +
> +/* ELM_ERROR_LOCATION_0-15 Registers */
> +#define ECC_ERROR_LOCATION_MASK		0x1fff
> +
> +#define ELM_ECC_SIZE			0x7ff
> +
> +#define SYNDROME_FRAGMENT_REG_SIZE	0x40
> +#define ERROR_LOCATION_SIZE		0x100
> +#define MAX_BCH_ELM_ERROR		16
> +#define ELM_FRAGMENT_REG		7
> +
> +typedef u32 syn_t[ELM_FRAGMENT_REG];
> +typedef u32 elm_error_t[MAX_BCH_ELM_ERROR];
> +
> +struct elm_info {
> +	struct device *dev;
> +	void __iomem *elm_base;
> +	struct completion elm_completion;
> +	struct list_head list;
> +	enum bch_ecc bch_type;
> +};
> +
> +static LIST_HEAD(elm_devices);
> +
> +static void elm_write_reg(void *offset, u32 val)
> +{
> +	writel(val, offset);
> +}
> +
> +static u32 elm_read_reg(void *offset)
> +{
> +	return readl(offset);
> +}
> +
> +/**
> + * elm_config - Configure ELM module
> + * @info:	elm info
> + */
> +static void elm_config(struct elm_info *info)
> +{
> +	u32 reg_val;
> +
> +	reg_val = (info->bch_type & ECC_BCH_LEVEL_MASK) | (ELM_ECC_SIZE << 16);
> +	elm_write_reg(info->elm_base + ELM_LOCATION_CONFIG, reg_val);
> +}
> +
> +/**
> + * elm_configure_page_mode - Enable/Disable page mode
> + * @info:	elm info
> + * @index:	index number of syndrome fragment vector
> + * @enable:	enable/disable flag for page mode
> + *
> + * Enable page mode for syndrome fragment index
> + */
> +static void elm_configure_page_mode(struct elm_info *info, int index,
> +		bool enable)
> +{
> +	u32 reg_val;
> +
> +	reg_val = elm_read_reg(info->elm_base + ELM_PAGE_CTRL);
> +	if (enable)
> +		reg_val |= BIT(index);	/* enable page mode */
> +	else
> +		reg_val &= ~BIT(index);	/* disable page mode */
> +
> +	elm_write_reg(info->elm_base + ELM_PAGE_CTRL, reg_val);
> +}
> +
> +static void rearrange_bch4(u8 *syndrome)
> +{
> +	/*
> +	 * BCH4 has 52 bit used for ecc, but OOB stored with
> +	 * nibble 0 appended, removes appended 0 nibble
> +	 */
> +	u64 *dst = (u64 *)syndrome;
> +	*dst >>= 4;
> +}
> +
> +/**
> + * elm_reverse_eccdata - Reverse ecc data
> + * @info:	elm info
> + * @ecc_data:	buffer for calculated ecc
> + * @syndrome:	buffer for syndrome polynomial
> + *
> + * ecc_data has to be reversed for syndrome vector
> + */
> +static void elm_reverse_eccdata(struct elm_info *info, u8 *ecc_data,
> +		u8 *syndrome)
> +{
> +	int i;
> +	int bch_size = info->bch_type ? BCH8_ECC_OOB_BYTES : BCH4_SIZE;
> +
> +	for (i = 0; i < bch_size; i++)
> +		syndrome[bch_size - 1 - i] = ecc_data[i];
> +
> +	/*
> +	 * syndrome polynomial to be rearranged for BCH 4 ecc scheme as 52
> +	 * bits being used and 4 bits being appended in syndrome vector
> +	 */
> +	if (info->bch_type == BCH4_ECC)
> +		rearrange_bch4(syndrome);
> +}
> +
> +/**
> + * elm_load_syndrome - Load ELM syndrome reg
> + * @info:	elm info
> + * @index:	syndrome fragment index
> + * @syndrome:	Syndrome polynomial
> + *
> + * Load syndrome fragment registers with syndrome polynomial
> + */
> +static void elm_load_syndrome(struct elm_info *info, int index, u8 *syndrome)
> +{
> +	int i;
> +	int max = info->bch_type ? BCH8_SYNDROME_SIZE : BCH4_SYNDROME_SIZE;
> +	void *syn_frag_base = info->elm_base + ELM_SYNDROME_FRAGMENT_0;
> +	syn_t *syn_fragment;
> +	u32 reg_val;
> +
> +	elm_configure_page_mode(info, index, true);
> +	syn_fragment = syn_frag_base + SYNDROME_FRAGMENT_REG_SIZE * index;
> +
> +	for (i = 0; i < max; i++) {
> +		reg_val = syndrome[0] | syndrome[1] << 8 | syndrome[2] << 16 |
> +			syndrome[3] << 24;
> +		elm_write_reg(*syn_fragment + i, reg_val);
> +		/* Update syndrome polynomial pointer */
> +		syndrome += 4;
> +	}
> +}
> +
> +/**
> + * elm_start_processing - start elm syndrome processing
> + * @info:	elm info
> + * @err_vec:	elm error vectors
> + *
> + * Set syndrome valid bit for syndrome fragment registers for which
> + * elm syndrome fragment registers are loaded. This enables elm module
> + * to start processing syndrome vectors.
> + */
> +static void elm_start_processing(struct elm_info *info,
> +		struct elm_errorvec *err_vec)
> +{
> +	int i;
> +	void *offset;
> +	u32 reg_val;
> +
> +	/*
> +	 * Set syndrome vector valid so that ELM module will process it for
> +	 * vectors error is reported
> +	 */
> +	for (i = 0; i < ERROR_VECTOR_MAX; i++) {
> +		if (err_vec[i].error_reported) {
> +			offset = info->elm_base + ELM_SYNDROME_FRAGMENT_6 + i *
> +				SYNDROME_FRAGMENT_REG_SIZE;
> +			reg_val = elm_read_reg(offset);
> +			reg_val |= ELM_SYNDROME_VALID;
> +			elm_write_reg(offset, reg_val);
> +		}
> +	}
> +}
> +
> +/**
> + * elm_error_correction - locate correctable error position
> + * @info:	elm info
> + * @err_vec:	elm error vectors
> + *
> + * On completion of processing by elm module, error location status
> + * register updated with correctable/uncorrectable error information.
> + * In case of correctable errors, number of errors located from
> + * elm location status register & read the these many positions from

should probably be: "... & read the positions from ..."?

> + * elm error location register.
> + */
> +static void elm_error_correction(struct elm_info *info,
> +		struct elm_errorvec *err_vec)
> +{
> +	int i, j, errors = 0;
> +	void *err_loc_base = info->elm_base + ELM_ERROR_LOCATION_0;
> +	elm_error_t *err_loc;
> +	void *offset;
> +	u32 reg_val;
> +
> +	for (i = 0; i < ERROR_VECTOR_MAX; i++) {
> +		/* check error reported */
> +		if (err_vec[i].error_reported) {
> +			offset = info->elm_base + ELM_LOCATION_STATUS +
> +				i * ERROR_LOCATION_SIZE;
> +			reg_val = elm_read_reg(offset);
> +			/* check correctable error or not */
> +			if (reg_val & ECC_CORRECTABLE_MASK) {
> +				err_loc = err_loc_base +
> +					i * ERROR_LOCATION_SIZE;
> +				/* read count of correctable errors */
> +				err_vec[i].error_count = reg_val &
> +					ECC_NB_ERRORS_MASK;
> +
> +				/* update the error locations in error vector */
> +				for (j = 0; j < err_vec[i].error_count; j++) {
> +
> +					reg_val = elm_read_reg(*err_loc + j);
> +					err_vec[i].error_loc[j] = reg_val &
> +						ECC_ERROR_LOCATION_MASK;
> +				}
> +
> +				errors += err_vec[i].error_count;
> +			} else {
> +				err_vec[i].error_uncorrectable++;
> +			}

extra braces above

> +
> +			/* clearing interrupts for processed error vectors */
> +			elm_write_reg(info->elm_base + ELM_IRQSTATUS, BIT(i));
> +
> +			/* disable page mode */
> +			elm_configure_page_mode(info, i, false);
> +		}
> +	}
> +
> +	return;
> +}
> +
> +/**
> + * elm_decode_bch_error_page - Locate error position
> + * @info:	elm info

should be dev, not info

> + * @ecc_calc:	calculated ECC bytes from GPMC
> + * @err_vec:	elm error vectors
> + *
> + * Called with one or greater reported and is vectors with error reported
> + * is updated in err_vec[].error_reported
> + */

I do not understand the statement "Called with one ..."

> +void elm_decode_bch_error_page(struct device *dev, u8 *ecc_calc,
> +		struct elm_errorvec *err_vec)
> +{
> +	int i;
> +	u8 syndrome[BCH_MAX_ECC_BYTES_PER_SECTOR] = {0}, *syn_p;
> +	struct elm_info *info = dev_get_drvdata(dev);
> +	u32 reg_val;
> +
> +	/* enable page mode interrupt */
> +	reg_val = elm_read_reg(info->elm_base + ELM_IRQSTATUS);
> +	elm_write_reg(info->elm_base + ELM_IRQSTATUS,
> +			reg_val & INTR_STATUS_PAGE_VALID);
> +	elm_write_reg(info->elm_base + ELM_IRQENABLE, INTR_EN_PAGE_MASK);
> +
> +	syn_p = syndrome;
> +	for (i = 0; i < ERROR_VECTOR_MAX; i++) {
> +		if (err_vec[i].error_reported) {
> +			elm_reverse_eccdata(info, ecc_calc, syn_p);
> +			elm_load_syndrome(info, i, syn_p);
> +		}
> +
> +		ecc_calc += info->bch_type ? BCH8_SIZE : BCH4_SIZE;
> +		syn_p += OOB_SECTOR_SIZE;
> +	}
> +
> +	elm_start_processing(info, err_vec);
> +
> +	/*
> +	 * In case of error reported, wait for ELM module to finish
> +	 * locating error correction
> +	 */
> +	wait_for_completion(&info->elm_completion);
> +
> +	/* disable page mode interrupt */
> +	reg_val = elm_read_reg(info->elm_base + ELM_IRQENABLE);
> +	elm_write_reg(info->elm_base + ELM_IRQENABLE,
> +			reg_val & ~INTR_EN_PAGE_MASK);
> +	elm_error_correction(info, err_vec);
> +}
> +EXPORT_SYMBOL(elm_decode_bch_error_page);
> +
> +static irqreturn_t elm_isr(int this_irq, void *dev_id)
> +{
> +	u32 reg_val;
> +	struct elm_info *info = dev_id;
> +
> +	reg_val = elm_read_reg(info->elm_base + ELM_IRQSTATUS);
> +
> +	/* all error vectors processed */
> +	if (reg_val & INTR_STATUS_PAGE_VALID) {
> +		elm_write_reg(info->elm_base + ELM_IRQSTATUS,
> +				reg_val & INTR_STATUS_PAGE_VALID);
> +		complete(&info->elm_completion);
> +		return IRQ_HANDLED;
> +	}
> +
> +	return IRQ_NONE;
> +}
> +
> +struct device *elm_request(enum bch_ecc bch_type)
> +{
> +	struct elm_info *info;
> +
> +	list_for_each_entry(info, &elm_devices, list) {
> +		if (info && info->dev) {
> +				info->bch_type = bch_type;
> +				elm_config(info);
> +				return info->dev;
> +		}
> +	}
> +
> +	return NULL;
> +}
> +EXPORT_SYMBOL(elm_request);
> +
> +static int __devinit elm_probe(struct platform_device *pdev)
> +{
> +	int ret = 0;
> +	struct resource *res, *irq;
> +	struct elm_info *info;
> +
> +	info = devm_kzalloc(&pdev->dev, sizeof(*info), GFP_KERNEL);
> +	if (!info) {
> +		dev_err(&pdev->dev, "failed to allocate memory\n");
> +		return -ENOMEM;
> +	}
> +
> +	info->dev = &pdev->dev;
> +
> +	irq = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
> +	if (!irq) {
> +		dev_err(&pdev->dev, "no irq resource defined\n");
> +		return -ENODEV;
> +	}
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	if (!res) {
> +		dev_err(&pdev->dev, "no memory resource defined\n");
> +		return -ENODEV;
> +	}
> +
> +
> +	info->elm_base = devm_request_and_ioremap(&pdev->dev, res);
> +	if (!info->elm_base)
> +		return -EADDRNOTAVAIL;
> +
> +
> +	ret = devm_request_irq(&pdev->dev, irq->start, elm_isr, 0,
> +			pdev->name, info);
> +	if (ret) {
> +		dev_err(&pdev->dev, "failure requesting irq %i\n", irq->start);
> +		return ret;
> +	}
> +
> +	pm_runtime_enable(&pdev->dev);
> +	if (pm_runtime_get_sync(&pdev->dev)) {
> +		ret = -EINVAL;
> +		pm_runtime_disable(&pdev->dev);
> +		dev_err(&pdev->dev, "can't enable clock\n");
> +		return ret;
> +	}
> +
> +	init_completion(&info->elm_completion);
> +	INIT_LIST_HEAD(&info->list);
> +	list_add(&info->list, &elm_devices);
> +	platform_set_drvdata(pdev, info);
> +	return ret;
> +}
> +
> +static int __devexit elm_remove(struct platform_device *pdev)
> +{
> +	pm_runtime_put_sync(&pdev->dev);
> +	pm_runtime_disable(&pdev->dev);
> +	platform_set_drvdata(pdev, NULL);
> +	return 0;
> +}
> +
> +
> +#ifdef CONFIG_OF
> +static const struct of_device_id elm_of_match[] = {
> +	{ .compatible = "ti,elm" },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, elm_of_match);
> +#endif
> +
> +static struct platform_driver elm_driver = {
> +	.driver		= {
> +		.name	= "elm",
> +		.of_match_table = of_match_ptr(elm_of_match),
> +		.owner	= THIS_MODULE,
> +	},
> +	.probe		= elm_probe,
> +	.remove		= __devexit_p(elm_remove),
> +};
> +
> +module_platform_driver(elm_driver);
> +
> +MODULE_DESCRIPTION("ELM driver for BCH error correction");
> +MODULE_AUTHOR("Texas Instruments");
> +MODULE_ALIAS("platform: elm");
> +MODULE_LICENSE("GPL v2");
> diff --git a/include/linux/platform_data/elm.h b/include/linux/platform_data/elm.h
> new file mode 100644
> index 0000000..eb53163
> --- /dev/null
> +++ b/include/linux/platform_data/elm.h
> @@ -0,0 +1,60 @@
> +/*
> + * BCH Error Location Module
> + *
> + * Copyright (C) 2012 Texas Instruments Incorporated - http://www.ti.com/
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + */
> +
> +#ifndef __ELM_H
> +#define __ELM_H
> +
> +enum bch_ecc {
> +	BCH4_ECC = 0,
> +	BCH8_ECC,
> +	BCH16_ECC,
> +};
> +
> +/* ELM support 8 error syndrome process */
> +#define ERROR_VECTOR_MAX		8
> +#define OOB_SECTOR_SIZE			16
> +
> +#define BCH_MAX_ECC_BYTES_PER_SECTOR	(OOB_SECTOR_SIZE * ERROR_VECTOR_MAX)
> +
> +#define BCH8_ECC_OOB_BYTES		13
> +/* RBL requires 14 byte even though BCH8 uses only 13 byte */

not sure what RBL is?

> +#define BCH8_SIZE			(BCH8_ECC_OOB_BYTES + 1)
> +#define BCH4_SIZE			7
> +
> +#define	BCH8_SYNDROME_SIZE		4	/* 13 bytes of ecc */
> +#define	BCH4_SYNDROME_SIZE		2	/* 7 bytes of ecc */
> +
> +/**
> + * struct elm_errorvec - error vector for elm
> + * @error_reported:		set true for vectors error is reported
> + *
> + * @error_count:		number of correctable errors in the sector
> + * @error_uncorrectable:	number of uncorrectable errors
> + * @error_loc:			buffer for error location
> + *
> + */
> +struct elm_errorvec {
> +	bool error_reported;
> +	int error_count;
> +	int error_uncorrectable;
> +	int error_loc[ERROR_VECTOR_MAX];
> +};
> +
> +void elm_decode_bch_error_page(struct device *dev, u8 *ecc_calc,
> +		struct elm_errorvec *err_vec);
> +struct device *elm_request(enum bch_ecc bch_type);
> +#endif /* __ELM_H */
> 

-- 

Peter Meerwald
+43-664-2444418 (mobile)