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Date:   Mon, 28 May 2018 00:04:22 +0200
From:   Miquel Raynal <miquel.raynal@bootlin.com>
To:     Stefan Agner <stefan@agner.ch>
Cc:     boris.brezillon@bootlin.com, dwmw2@infradead.org,
        computersforpeace@gmail.com, marek.vasut@gmail.com,
        robh+dt@kernel.org, mark.rutland@arm.com, thierry.reding@gmail.com,
        mturquette@baylibre.com, sboyd@kernel.org, dev@lynxeye.de,
        richard@nod.at, marcel@ziswiler.com, krzk@kernel.org,
        digetx@gmail.com, benjamin.lindqvist@endian.se,
        jonathanh@nvidia.com, pdeschrijver@nvidia.com, pgaikwad@nvidia.com,
        mirza.krak@gmail.com, linux-mtd@lists.infradead.org,
        linux-tegra@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-clk@vger.kernel.org
Subject: Re: [RESEND PATCH 2/5] mtd: rawnand: add NVIDIA Tegra NAND Flash
 controller driver
Message-ID: <20180528000422.7f18dc5f@xps13>
In-Reply-To: <86fdf19ec92b732709732fb60199f16488b4b727.1526990589.git.stefan@agner.ch>
References: <cover.1526990589.git.stefan@agner.ch>
        <86fdf19ec92b732709732fb60199f16488b4b727.1526990589.git.stefan@agner.ch>
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Sender: linux-kernel-owner@vger.kernel.org
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Hi Stefan,

I just see your v2 while I'm sending my review on the driver, will
probably wait for v4 then ;)

Thanks for the work though!
Miquèl

On Tue, 22 May 2018 14:07:06 +0200, Stefan Agner <stefan@agner.ch>
wrote:

> Add support for the NAND flash controller found on NVIDIA
> Tegra 2 SoCs. This implementation does not make use of the
> command queue feature. Regular operations/data transfers are
> done in PIO mode. Page read/writes with hardware ECC make
> use of the DMA for data transfer.
> 
> Signed-off-by: Lucas Stach <dev@lynxeye.de>
> Signed-off-by: Stefan Agner <stefan@agner.ch>
> ---

[...]

> --- /dev/null
> +++ b/drivers/mtd/nand/raw/tegra_nand.c
> @@ -0,0 +1,915 @@
> +/*
> + * Copyright (C) 2018 Stefan Agner <stefan@agner.ch>
> + * Copyright (C) 2014-2015 Lucas Stach <dev@lynxeye.de>
> + * Copyright (C) 2012 Avionic Design GmbH
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.

Please use SPDX tag.

> + */
> +
> +#include <linux/clk.h>
> +#include <linux/completion.h>
> +#include <linux/delay.h>
> +#include <linux/dma-mapping.h>
> +#include <linux/err.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/interrupt.h>
> +#include <linux/io.h>
> +#include <linux/module.h>
> +#include <linux/mtd/partitions.h>
> +#include <linux/mtd/rawnand.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/reset.h>
> +
> +#define CMD					0x00
> +#define   CMD_GO				(1 << 31)
> +#define   CMD_CLE				(1 << 30)
> +#define   CMD_ALE				(1 << 29)
> +#define   CMD_PIO				(1 << 28)
> +#define   CMD_TX				(1 << 27)
> +#define   CMD_RX				(1 << 26)

Please use the BIT(x) macro instead of (1 << x)

> +#define   CMD_SEC_CMD				(1 << 25)
> +#define   CMD_AFT_DAT				(1 << 24)
> +#define   CMD_TRANS_SIZE(x)			(((x - 1) & 0xf) << 20)
> +#define   CMD_A_VALID				(1 << 19)
> +#define   CMD_B_VALID				(1 << 18)
> +#define   CMD_RD_STATUS_CHK			(1 << 17)
> +#define   CMD_RBSY_CHK				(1 << 16)
> +#define   CMD_CE(x)				(1 << (8 + ((x) & 0x7)))
> +#define   CMD_CLE_SIZE(x)			(((x - 1) & 0x3) << 4)
> +#define   CMD_ALE_SIZE(x)			(((x - 1) & 0xf) << 0)
> +

[...]

> +static int tegra_nand_cmd(struct nand_chip *chip,
> +			 const struct nand_subop *subop)
> +{
> +	const struct nand_op_instr *instr;
> +	const struct nand_op_instr *instr_data_in = NULL;
> +	struct mtd_info *mtd = nand_to_mtd(chip);
> +	struct tegra_nand *nand = to_tegra_nand(mtd);
> +	unsigned int op_id = -1, trfr_in_sz = 0, trfr_out_sz = 0, offset = 0;
> +	bool first_cmd = true;
> +	bool force8bit;
> +	u32 cmd = 0;
> +	u32 value;
> +
> +	for (op_id = 0; op_id < subop->ninstrs; op_id++) {
> +		unsigned int naddrs, i;
> +		const u8 *addrs;
> +		u32 addr1 = 0, addr2 = 0;
> +
> +		instr = &subop->instrs[op_id];
> +
> +		switch (instr->type) {
> +		case NAND_OP_CMD_INSTR:
> +			if (first_cmd) {
> +				cmd |= CMD_CLE;
> +				writel(instr->ctx.cmd.opcode, nand->regs + CMD_1);
> +			} else {
> +				cmd |= CMD_SEC_CMD;
> +				writel(instr->ctx.cmd.opcode, nand->regs + CMD_2);
> +			}
> +			first_cmd = false;
> +			break;
> +		case NAND_OP_ADDR_INSTR:
> +			offset = nand_subop_get_addr_start_off(subop, op_id);
> +			naddrs = nand_subop_get_num_addr_cyc(subop, op_id);
> +			addrs = &instr->ctx.addr.addrs[offset];
> +
> +			cmd |= CMD_ALE | CMD_ALE_SIZE(naddrs);
> +			for (i = 0; i < min_t(unsigned int, 4, naddrs); i++)
> +				addr1 |= *addrs++ << (8 * i);
> +			naddrs -= i;
> +			for (i = 0; i < min_t(unsigned int, 4, naddrs); i++)
> +				addr2 |= *addrs++ << (8 * i);
> +			writel(addr1, nand->regs + ADDR_1);
> +			writel(addr2, nand->regs + ADDR_2);
> +			break;
> +
> +		case NAND_OP_DATA_IN_INSTR:
> +			trfr_in_sz = nand_subop_get_data_len(subop, op_id);
> +			offset = nand_subop_get_data_start_off(subop, op_id);
> +
> +			cmd |= CMD_TRANS_SIZE(trfr_in_sz) | CMD_PIO | CMD_RX | CMD_A_VALID;
> +
> +			instr_data_in = instr;
> +			break;
> +
> +		case NAND_OP_DATA_OUT_INSTR:
> +			trfr_out_sz = nand_subop_get_data_len(subop, op_id);
> +			offset = nand_subop_get_data_start_off(subop, op_id);
> +			trfr_out_sz = min_t(size_t, trfr_out_sz, 4);
> +
> +			cmd |= CMD_TRANS_SIZE(trfr_out_sz) | CMD_PIO | CMD_TX | CMD_A_VALID;
> +
> +			memcpy(&value, instr->ctx.data.buf.out + offset, trfr_out_sz);
> +			writel(value, nand->regs + RESP);
> +
> +			break;
> +		case NAND_OP_WAITRDY_INSTR:
> +			cmd |= CMD_RBSY_CHK;
> +			break;
> +
> +		}
> +	}
> +
> +
> +	cmd |= CMD_GO | CMD_CE(nand->cur_chip);
> +	writel(cmd, nand->regs + CMD);
> +	wait_for_completion(&nand->command_complete);

_timeout?

> +
> +	if (instr_data_in) {
> +		u32 value;
> +		size_t n = min_t(size_t, trfr_in_sz, 4);
> +
> +		value = readl(nand->regs + RESP);
> +		memcpy(instr_data_in->ctx.data.buf.in + offset, &value, n);
> +	}
> +
> +	return 0;
> +}
> +
> +static const struct nand_op_parser tegra_nand_op_parser = NAND_OP_PARSER(
> +	NAND_OP_PARSER_PATTERN(tegra_nand_cmd,
> +		NAND_OP_PARSER_PAT_CMD_ELEM(true),
> +		NAND_OP_PARSER_PAT_ADDR_ELEM(true, 8),
> +		NAND_OP_PARSER_PAT_CMD_ELEM(true),
> +		NAND_OP_PARSER_PAT_WAITRDY_ELEM(true)),
> +	NAND_OP_PARSER_PATTERN(tegra_nand_cmd,
> +		NAND_OP_PARSER_PAT_DATA_OUT_ELEM(false, 4)),
> +	NAND_OP_PARSER_PATTERN(tegra_nand_cmd,
> +		NAND_OP_PARSER_PAT_CMD_ELEM(true),
> +		NAND_OP_PARSER_PAT_ADDR_ELEM(true, 8),
> +		NAND_OP_PARSER_PAT_CMD_ELEM(true),
> +		NAND_OP_PARSER_PAT_WAITRDY_ELEM(true),
> +		NAND_OP_PARSER_PAT_DATA_IN_ELEM(true, 4)),
> +	);
> +
> +static int tegra_nand_exec_op(struct nand_chip *chip,
> +			     const struct nand_operation *op,
> +			     bool check_only)
> +{
> +	return nand_op_parser_exec_op(chip, &tegra_nand_op_parser, op,
> +				      check_only);
> +}
> +static void tegra_nand_select_chip(struct mtd_info *mtd, int chip)
> +{
> +	struct tegra_nand *nand = to_tegra_nand(mtd);
> +
> +	nand->cur_chip = chip;

You should probably save the timings configuration and apply them back
here in case of using different chips.

> +}
> +
> +static u32 tegra_nand_fill_address(struct mtd_info *mtd, struct nand_chip *chip,
> +				   int page)
> +{
> +	struct tegra_nand *nand = to_tegra_nand(mtd);
> +
> +	/* Lower 16-bits are column, always 0 */
> +	writel(page << 16, nand->regs + ADDR_1);
> +
> +	if (chip->options & NAND_ROW_ADDR_3) {
> +		writel(page >> 16, nand->regs + ADDR_2);
> +		return 5;
> +	}
> +
> +	return 4;
> +}
> +
> +static int tegra_nand_read_page(struct mtd_info *mtd, struct nand_chip *chip,
> +				uint8_t *buf, int oob_required, int page)
> +{
> +	struct tegra_nand *nand = to_tegra_nand(mtd);
> +	u32 value, addrs;
> +
> +	writel(NAND_CMD_READ0, nand->regs + CMD_1);
> +	writel(NAND_CMD_READSTART, nand->regs + CMD_2);
> +
> +	addrs = tegra_nand_fill_address(mtd, chip, page);
> +
> +	value = readl(nand->regs + CFG);
> +	value |= CFG_HW_ECC | CFG_ERR_COR;
> +	writel(value, nand->regs + CFG);
> +
> +	writel(mtd->writesize - 1, nand->regs + DMA_CFG_A);
> +	writel(nand->data_dma, nand->regs + DATA_PTR);
> +
> +	if (oob_required) {
> +		writel(mtd_ooblayout_count_freebytes(mtd) - 1,
> +		       nand->regs + DMA_CFG_B);
> +		writel(nand->oob_dma, nand->regs + TAG_PTR);
> +	} else {
> +		writel(0, nand->regs + DMA_CFG_B);
> +		writel(0, nand->regs + TAG_PTR);
> +	}
> +
> +	value = DMA_CTRL_GO | DMA_CTRL_IN | DMA_CTRL_PERF_EN |
> +		DMA_CTRL_REUSE | DMA_CTRL_IE_DONE | DMA_CTRL_IS_DONE |
> +		DMA_CTRL_BURST_8 | DMA_CTRL_EN_A;
> +	if (oob_required)
> +		value |= DMA_CTRL_EN_B;
> +	writel(value, nand->regs + DMA_CTRL);
> +
> +	value = CMD_CLE | CMD_ALE | CMD_ALE_SIZE(addrs) | CMD_SEC_CMD |
> +		CMD_RBSY_CHK | CMD_GO | CMD_RX | CMD_TRANS_SIZE(9) |
> +		CMD_A_VALID | CMD_CE(nand->cur_chip);
> +	if (oob_required)
> +		value |= CMD_B_VALID;
> +	writel(value, nand->regs + CMD);
> +
> +	wait_for_completion(&nand->command_complete);
> +	wait_for_completion(&nand->dma_complete);
> +
> +	if (oob_required) {
> +		struct mtd_oob_region oobregion;
> +
> +		mtd_ooblayout_free(mtd, 0, &oobregion);

Don't you want to save the oobregion parameters once and then just
refer to them?

> +		memcpy(chip->oob_poi, nand->oob_buf + oobregion.offset,
> +		       mtd_ooblayout_count_freebytes(mtd));
> +	}
> +	memcpy(buf, nand->data_buf, mtd->writesize);
> +
> +	value = readl(nand->regs + CFG);
> +	value &= ~(CFG_HW_ECC | CFG_ERR_COR);
> +	writel(value, nand->regs + CFG);
> +
> +	value = readl(nand->regs + DEC_STATUS);
> +	if (value & DEC_STATUS_A_ECC_FAIL) {
> +		/*
> +		 * The ECC isn't smart enough to figure out if a page is
> +		 * completely erased and flags an error in this case. So we
> +		 * check the read data here to figure out if it's a legitimate
> +		 * error or a false positive.
> +		 */
> +		int i, err;
> +		int flips_threshold = chip->ecc.strength / 2;
> +		int max_bitflips = 0;
> +
> +		for (i = 0; i < chip->ecc.steps; i++) {
> +			u8 *data = buf + (chip->ecc.size * i);
> +			err = nand_check_erased_ecc_chunk(data, chip->ecc.size,

Are you sure the data was uncorrected there? I bet you have corrected
data in chip->ecc.size and should re-read the page with the raw
helpers before using nand_check_erased_ecc_chunk().
 
> +							  NULL, 0,
> +							  NULL, 0,
> +							  flips_threshold);

I think you should use chip->ecc.strength instead of flips_threshold
(and remove it).

> +			if (err < 0)
> +				return err;

In case of ECC failure you should increment ecc_stats.failed.

> +
> +			max_bitflips += max_bitflips;

max_bitflipts = max_t(unsigned int, max_bitflipts, err);

> +		}
> +
> +		return max_bitflips;
> +	}
> +
> +	if (nand->last_read_error) {
> +		int max_corr_cnt, corr_sec_flag;
> +
> +		value = readl(nand->regs + DEC_STAT_BUF);
> +		corr_sec_flag = (value & DEC_STAT_BUF_CORR_SEC_FLAG_MASK) >>
> +				DEC_STAT_BUF_CORR_SEC_FLAG_SHIFT;
> +		max_corr_cnt = (value & DEC_STAT_BUF_MAX_CORR_CNT_MASK) >>
> +			       DEC_STAT_BUF_MAX_CORR_CNT_SHIFT;
> +
> +		/*
> +		 * The value returned in the register is the maximum of
> +		 * bitflips encountered in any of the ECC regions. As there is
> +		 * no way to get the number of bitflips in a specific regions
> +		 * we are not able to deliver correct stats but instead
> +		 * overestimate the number of corrected bitflips by assuming
> +		 * that all regions where errors have been corrected
> +		 * encountered the maximum number of bitflips.
> +		 */
> +		mtd->ecc_stats.corrected += max_corr_cnt * hweight8(corr_sec_flag);

That's bad. But okay if we don't have the information.

> +		nand->last_read_error = false;
> +		return value;
> +	}
> +
> +	return 0;
> +}
> +
> +static int tegra_nand_write_page(struct mtd_info *mtd, struct nand_chip *chip,
> +				 const uint8_t *buf, int oob_required, int page)
> +{
> +	struct tegra_nand *nand = to_tegra_nand(mtd);
> +	u32 value, addrs;
> +
> +	writel(NAND_CMD_SEQIN, nand->regs + CMD_1);
> +	writel(NAND_CMD_PAGEPROG, nand->regs + CMD_2);
> +
> +	addrs = tegra_nand_fill_address(mtd, chip, page);
> +
> +	value = readl(nand->regs + CFG);
> +	value |= CFG_HW_ECC | CFG_ERR_COR;
> +	writel(value, nand->regs + CFG);

You might want to test with the _relaxed() operators?

> +
> +	memcpy(nand->data_buf, buf, mtd->writesize);
> +
> +	writel(mtd->writesize - 1, nand->regs + DMA_CFG_A);
> +	writel(nand->data_dma, nand->regs + DATA_PTR);
> +
> +	if (oob_required) {
> +		struct mtd_oob_region oobregion;
> +
> +		mtd_ooblayout_free(mtd, 0, &oobregion);
> +		memcpy(nand->oob_buf, chip->oob_poi + oobregion.offset,
> +		       mtd_ooblayout_count_freebytes(mtd));
> +		writel(mtd_ooblayout_count_freebytes(mtd) - 1,
> +		       nand->regs + DMA_CFG_B);
> +		writel(nand->oob_dma, nand->regs + TAG_PTR);
> +	} else {
> +		writel(0, nand->regs + DMA_CFG_B);
> +		writel(0, nand->regs + TAG_PTR);
> +	}
> +
> +	value = DMA_CTRL_GO | DMA_CTRL_OUT | DMA_CTRL_PERF_EN |
> +		DMA_CTRL_IE_DONE | DMA_CTRL_IS_DONE |
> +		DMA_CTRL_BURST_8 | DMA_CTRL_EN_A;
> +	if (oob_required)
> +		value |= DMA_CTRL_EN_B;

Line here

> +	writel(value, nand->regs + DMA_CTRL);
> +
> +	value = CMD_CLE | CMD_ALE | CMD_ALE_SIZE(addrs) | CMD_SEC_CMD |
> +		CMD_AFT_DAT | CMD_RBSY_CHK | CMD_GO | CMD_TX | CMD_A_VALID |
> +		CMD_TRANS_SIZE(9) | CMD_CE(nand->cur_chip);
> +	if (oob_required)
> +		value |= CMD_B_VALID;

Line here

> +	writel(value, nand->regs + CMD);
> +
> +	wait_for_completion(&nand->command_complete);
> +	wait_for_completion(&nand->dma_complete);
> +
> +	value = readl(nand->regs + CFG);
> +	value &= ~(CFG_HW_ECC | CFG_ERR_COR);
> +	writel(value, nand->regs + CFG);
> +
> +	return 0;
> +}
> +
> +static void tegra_nand_setup_timing(struct tegra_nand *nand, int mode)
> +{
> +	/*
> +	 * The period (and all other timings in this function) is in ps,
> +	 * so need to take care here to avoid integer overflows.

You might wanna check __DIVIDE, PSEC_TO_NSEC and PSEC_TO_MSEC macros in
rawnand.h. You could use them in the following derivations.

> +	 */
> +	unsigned int rate = clk_get_rate(nand->clk) / 1000000;
> +	unsigned int period = DIV_ROUND_UP(1000000, rate);
> +	const struct nand_sdr_timings *timings;
> +	u32 val, reg = 0;
> +
> +	timings = onfi_async_timing_mode_to_sdr_timings(mode);
> +
> +	val = DIV_ROUND_UP(max3(timings->tAR_min, timings->tRR_min,
> +				timings->tRC_min), period);
> +	if (val > 2)
> +		val -= 3;
> +	reg |= TIMING_TCR_TAR_TRR(val);
> +
> +	val = DIV_ROUND_UP(max(max(timings->tCS_min, timings->tCH_min),
> +				   max(timings->tALS_min, timings->tALH_min)),

Is the second line aligned correctly?

> +			   period);
> +	if (val > 1)
> +		val -= 2;

This is weird and I would recommend a comment.

> +	reg |= TIMING_TCS(val);
> +
> +	val = DIV_ROUND_UP(max(timings->tRP_min, timings->tREA_max) + 6000,
> +			   period);
> +	reg |= TIMING_TRP(val) | TIMING_TRP_RESP(val);
> +
> +	reg |= TIMING_TWB(DIV_ROUND_UP(timings->tWB_max, period));
> +	reg |= TIMING_TWHR(DIV_ROUND_UP(timings->tWHR_min, period));
> +	reg |= TIMING_TWH(DIV_ROUND_UP(timings->tWH_min, period));
> +	reg |= TIMING_TWP(DIV_ROUND_UP(timings->tWP_min, period));
> +	reg |= TIMING_TRH(DIV_ROUND_UP(timings->tRHW_min, period));
> +
> +	writel(reg, nand->regs + TIMING_1);
> +
> +	val = DIV_ROUND_UP(timings->tADL_min, period);
> +	if (val > 2)
> +		val -= 3;

Ditto

> +	reg = TIMING_TADL(val);
> +
> +	writel(reg, nand->regs + TIMING_2);
> +}
> +
> +static void tegra_nand_setup_chiptiming(struct tegra_nand *nand)
> +{
> +	struct nand_chip *chip = &nand->chip;
> +	int mode;
> +
> +	mode = onfi_get_async_timing_mode(chip);
> +	if (mode == ONFI_TIMING_MODE_UNKNOWN)
> +		mode = chip->onfi_timing_mode_default;
> +	else
> +		mode = fls(mode);
> +
> +	tegra_nand_setup_timing(nand, mode);
> +}

You can drop this function and use tegra_nand_setup_timing directly as
hook for ->setup_data_interface().

> +
> +static int tegra_nand_probe(struct platform_device *pdev)
> +{
> +	struct reset_control *rst;
> +	struct tegra_nand *nand;

Would you mind having another name for the tegra_nand structure than
just 'nand'? I found it confusing as, following Boris comment, it won't
be a 'NAND device' structure but rather more a controller structure.

> +	struct nand_chip *chip;
> +	struct mtd_info *mtd;
> +	struct resource *res;
> +	unsigned long value;

s/value/reg/ ? or something more explicit?

> +	int irq, err = 0;
> +
> +	nand = devm_kzalloc(&pdev->dev, sizeof(*nand), GFP_KERNEL);
> +	if (!nand)
> +		return -ENOMEM;
> +
> +	nand->dev = &pdev->dev;
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	nand->regs = devm_ioremap_resource(&pdev->dev, res);
> +	if (IS_ERR(nand->regs))
> +		return PTR_ERR(nand->regs);
> +
> +	irq = platform_get_irq(pdev, 0);
> +	err = devm_request_irq(&pdev->dev, irq, tegra_nand_irq, 0,
> +			       dev_name(&pdev->dev), nand);
> +	if (err)
> +		return err;
> +
> +	rst = devm_reset_control_get(&pdev->dev, "nand");
> +	if (IS_ERR(rst))
> +		return PTR_ERR(rst);
> +
> +	nand->clk = devm_clk_get(&pdev->dev, "nand");
> +	if (IS_ERR(nand->clk))
> +		return PTR_ERR(nand->clk);
> +
> +	nand->wp_gpio = gpiod_get_optional(&pdev->dev, "wp-gpios",
> +					   GPIOD_OUT_HIGH);
> +	if (IS_ERR(nand->wp_gpio))
> +		return PTR_ERR(nand->wp_gpio);
> +
> +	err = clk_prepare_enable(nand->clk);
> +	if (err)
> +		return err;
> +
> +	reset_control_assert(rst);
> +	udelay(2);
> +	reset_control_deassert(rst);
> +
> +	value = HWSTATUS_RDSTATUS_MASK(1) | HWSTATUS_RDSTATUS_VALUE(0) |
> +		HWSTATUS_RBSY_MASK(NAND_STATUS_READY) |
> +		HWSTATUS_RBSY_VALUE(NAND_STATUS_READY);
> +	writel(NAND_CMD_STATUS, nand->regs + HWSTATUS_CMD);
> +	writel(value, nand->regs + HWSTATUS_MASK);
> +
> +	init_completion(&nand->command_complete);
> +	init_completion(&nand->dma_complete);
> +
> +	/* clear interrupts */
> +	value = readl(nand->regs + ISR);
> +	writel(value, nand->regs + ISR);
> +
> +	writel(DMA_CTRL_IS_DONE, nand->regs + DMA_CTRL);
> +
> +	/* enable interrupts */
> +	value = IER_UND | IER_OVR | IER_CMD_DONE | IER_ECC_ERR | IER_GIE;
> +	writel(value, nand->regs + IER);
> +
> +	/* reset config */
> +	writel(0, nand->regs + CFG);
> +
> +	chip = &nand->chip;
> +	mtd = nand_to_mtd(chip);
> +
> +	mtd->dev.parent = &pdev->dev;
> +	mtd->name = "tegra_nand";

I just figured it was undocumented (yet) but you could have a label
string property in your nand DT node that tells you the name of the
MTD device instead of something too generic like tegra_nand.

> +	mtd->owner = THIS_MODULE;
> +
> +	nand_set_flash_node(chip, pdev->dev.of_node);
> +	nand_set_controller_data(chip, nand);
> +
> +	chip->options = NAND_NO_SUBPAGE_WRITE;
> +	chip->exec_op = tegra_nand_exec_op;
> +	chip->select_chip = tegra_nand_select_chip;
> +	tegra_nand_setup_timing(nand, 0);

You really should implement ->setup_data_interface() and let the core
handle the timings issue entirely (mind that chipnr is not the NAND
chip id but more the CS id asserted for the pointed NAND chip).
 
> +
> +	err = nand_scan_ident(mtd, 1, NULL);
> +	if (err)
> +		goto err_disable_clk;
> +
> +	if (chip->bbt_options & NAND_BBT_USE_FLASH)
> +		chip->bbt_options |= NAND_BBT_NO_OOB;
> +
> +	nand->data_buf = dmam_alloc_coherent(&pdev->dev, mtd->writesize,
> +					    &nand->data_dma, GFP_KERNEL);

Do you need these buffers before nand_scan_tail() or could you simply
use the ones allocated by the core right after?

> +	if (!nand->data_buf) {
> +		err = -ENOMEM;
> +		goto err_disable_clk;
> +	}
> +
> +	nand->oob_buf = dmam_alloc_coherent(&pdev->dev, mtd->oobsize,
> +					    &nand->oob_dma, GFP_KERNEL);
> +	if (!nand->oob_buf) {
> +		err = -ENOMEM;
> +		goto err_disable_clk;
> +	}
> +
> +	chip->ecc.mode = NAND_ECC_HW;
> +	chip->ecc.size = 512;
> +	chip->ecc.read_page = tegra_nand_read_page;
> +	chip->ecc.write_page = tegra_nand_write_page;
> +
> +	value = readl(nand->regs + CFG);
> +	value |= CFG_PIPE_EN | CFG_SKIP_SPARE | CFG_SKIP_SPARE_SIZE_4 |
> +		 CFG_TAG_BYTE_SIZE(mtd_ooblayout_count_freebytes(mtd) - 1);
> +
> +	if (chip->options & NAND_BUSWIDTH_16)
> +		value |= CFG_BUS_WIDTH_16;
> +
> +	switch (mtd->oobsize) {
> +	case 16:
> +		mtd_set_ooblayout(mtd, &tegra_nand_oob_16_ops);
> +		chip->ecc.strength = 1;
> +		chip->ecc.bytes = 4;
> +		break;
> +	case 64:
> +		mtd_set_ooblayout(mtd, &tegra_nand_oob_64_ops);
> +		chip->ecc.strength = 8;
> +		chip->ecc.bytes = 18;
> +		value |= CFG_ECC_SEL | CFG_TVAL_8;
> +		break;
> +	case 128:
> +		mtd_set_ooblayout(mtd, &tegra_nand_oob_128_ops);
> +		chip->ecc.strength = 8;
> +		chip->ecc.bytes = 18;
> +		value |= CFG_ECC_SEL | CFG_TVAL_8;
> +		break;
> +	case 224:
> +		mtd_set_ooblayout(mtd, &tegra_nand_oob_224_ops);
> +		chip->ecc.strength = 8;
> +		chip->ecc.bytes = 18;
> +		value |= CFG_ECC_SEL | CFG_TVAL_8;
> +		break;
> +	default:
> +		dev_err(&pdev->dev, "unhandled OOB size %d\n", mtd->oobsize);
> +		err = -ENODEV;
> +		goto err_disable_clk;
> +	}
> +
> +	switch (mtd->writesize) {
> +	case 256:
> +		value |= CFG_PS_256;
> +		break;
> +	case 512:
> +		value |= CFG_PS_512;
> +		break;
> +	case 1024:
> +		value |= CFG_PS_1024;
> +		break;
> +	case 2048:
> +		value |= CFG_PS_2048;
> +		break;
> +	case 4096:
> +		value |= CFG_PS_4096;
> +		break;
> +	default:
> +		dev_err(&pdev->dev, "unhandled writesize %d\n", mtd->writesize);
> +		err = -ENODEV;
> +		goto err_disable_clk;
> +	}
> +
> +	writel(value, nand->regs + CFG);
> +
> +	tegra_nand_setup_chiptiming(nand);
> +
> +	err = nand_scan_tail(mtd);
> +	if (err)
> +		goto err_disable_clk;
> +
> +	err = mtd_device_register(mtd, NULL, 0);
> +	if (err)
> +		goto err_cleanup_nand;
> +
> +	platform_set_drvdata(pdev, nand);
> +
> +	return 0;
> +
> +err_cleanup_nand:
> +	nand_cleanup(chip);
> +err_disable_clk:
> +	clk_disable_unprepare(nand->clk);
> +	return err;
> +}
> +
> +static int tegra_nand_remove(struct platform_device *pdev)
> +{
> +	struct tegra_nand *nand = platform_get_drvdata(pdev);
> +
> +	nand_release(nand_to_mtd(&nand->chip));
> +
> +	clk_disable_unprepare(nand->clk);
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id tegra_nand_of_match[] = {
> +	{ .compatible = "nvidia,tegra20-nand" },
> +	{ /* sentinel */ }
> +};
> +
> +static struct platform_driver tegra_nand_driver = {
> +	.driver = {
> +		.name = "tegra-nand",
> +		.of_match_table = tegra_nand_of_match,
> +	},
> +	.probe = tegra_nand_probe,
> +	.remove = tegra_nand_remove,
> +};
> +module_platform_driver(tegra_nand_driver);
> +
> +MODULE_DESCRIPTION("NVIDIA Tegra NAND driver");
> +MODULE_AUTHOR("Thierry Reding <thierry.reding@nvidia.com>");
> +MODULE_AUTHOR("Lucas Stach <dev@lynxeye.de>");
> +MODULE_AUTHOR("Stefan Agner <stefan@agner.ch>");
> +MODULE_LICENSE("GPL v2");
> +MODULE_DEVICE_TABLE(of, tegra_nand_of_match);