Date:	Sat, 13 Aug 2016 00:37:03 +0200
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	Kyle Roeschley <kyle.roeschley@...com>
Cc:	richard@....at, dwmw2@...radead.org, computersforpeace@...il.com,
	beanhuo@...ron.com, linux-mtd@...ts.infradead.org,
	linux-kernel@...r.kernel.org, nathan.sullivan@...com,
	xander.huff@...com, peterpansjtu@...il.com
Subject: Re: [PATCH v7 1/2] mtd: nand_bbt: Move BBT block selection logic
 out of write_bbt()

On Fri, 12 Aug 2016 16:58:22 -0500
Kyle Roeschley <kyle.roeschley@...com> wrote:

> From: Boris Brezillon <boris.brezillon@...e-electrons.com>
> 
> This clarifies the write_bbt() by removing the write label and
> clarifying the error/exit path.
> 
> Signed-off-by: Boris Brezillon <boris.brezillon@...e-electrons.com>
> Tested-by: Kyle Roeschley <kyle.roeschley@...com>
> ---
> v7: Move all code cleanup into first patch
>     Correct documentation of mark_bbt_block_bad
>     Make pr_warn messages consistent
>     Add Tested-bys
> 
> v6: Split functionality of write_bbt out into new functions
> 
> v5: De-duplicate bad block handling
> 
> v4: Don't ignore write protection while marking bad BBT blocks
>     Correctly call block_markbad
>     Minor cleanups
> 
> v3: Don't overload mtd->priv
>     Keep nand_erase_nand from erroring on protected BBT blocks
> 
> v2: Mark OOB area in each block as well as BBT
>     Avoid marking read-only, bad address, or known bad blocks as bad
> 
>  drivers/mtd/nand/nand_bbt.c | 114 +++++++++++++++++++++++++++++---------------
>  1 file changed, 76 insertions(+), 38 deletions(-)
> 
> diff --git a/drivers/mtd/nand/nand_bbt.c b/drivers/mtd/nand/nand_bbt.c
> index 2fbb523..918db24 100644
> --- a/drivers/mtd/nand/nand_bbt.c
> +++ b/drivers/mtd/nand/nand_bbt.c
> @@ -605,6 +605,69 @@ static void search_read_bbts(struct mtd_info *mtd, uint8_t *buf,
>  }
>  
>  /**
> + * get_bbt_block - Get the first valid eraseblock suitable to store a BBT
> + * @this: the NAND device
> + * @td: the BBT description
> + * @md: the mirror BBT descriptor
> + * @chip: the CHIP selector
> + *
> + * This functions returns a positive block number pointing a valid eraseblock
> + * suitable to store a BBT (i.e. in the range reserved for BBT), or -ENOSPC if
> + * all blocks are already used of marked bad. If td->pages[chip] was already
> + * pointing to a valid block we re-use it, otherwise we search for the next
> + * valid one.
> + */
> +static int get_bbt_block(struct nand_chip *this, struct nand_bbt_descr *td,
> +			 struct nand_bbt_descr *md, int chip)
> +{
> +	int startblock, dir, page, numblocks, i;
> +
> +	/*
> +	 * There was already a version of the table, reuse the page. This
> +	 * applies for absolute placement too, as we have the page number in
> +	 * td->pages.
> +	 */
> +	if (td->pages[chip] != -1)
> +		return td->pages[chip] >>
> +				(this->bbt_erase_shift - this->page_shift);
> +
> +	numblocks = (int)(this->chipsize >> this->bbt_erase_shift);
> +	if (!(td->options & NAND_BBT_PERCHIP))
> +		numblocks *= this->numchips;
> +
> +	/*
> +	 * Automatic placement of the bad block table. Search direction
> +	 * top -> down?
> +	 */
> +	if (td->options & NAND_BBT_LASTBLOCK) {
> +		startblock = numblocks * (chip + 1) - 1;
> +		dir = -1;
> +	} else {
> +		startblock = chip * numblocks;
> +		dir = 1;
> +	}
> +
> +	for (i = 0; i < td->maxblocks; i++) {
> +		int block = startblock + dir * i;
> +
> +		/* Check, if the block is bad */
> +		switch (bbt_get_entry(this, block)) {
> +		case BBT_BLOCK_WORN:
> +		case BBT_BLOCK_FACTORY_BAD:
> +			continue;
> +		}
> +
> +		page = block << (this->bbt_erase_shift - this->page_shift);
> +
> +		/* Check, if the block is used by the mirror table */
> +		if (!md || md->pages[chip] != page)
> +			return block;
> +	}
> +
> +	return -ENOSPC;
> +}
> +
> +/**
>   * write_bbt - [GENERIC] (Re)write the bad block table
>   * @mtd: MTD device structure
>   * @buf: temporary buffer
> @@ -621,7 +684,7 @@ static int write_bbt(struct mtd_info *mtd, uint8_t *buf,
>  	struct nand_chip *this = mtd_to_nand(mtd);
>  	struct erase_info einfo;
>  	int i, res, chip = 0;
> -	int bits, startblock, dir, page, offs, numblocks, sft, sftmsk;
> +	int bits, page, offs, numblocks, sft, sftmsk;
>  	int nrchips, pageoffs, ooboffs;
>  	uint8_t msk[4];
>  	uint8_t rcode = td->reserved_block_code;
> @@ -652,46 +715,21 @@ static int write_bbt(struct mtd_info *mtd, uint8_t *buf,
>  	}
>  
>  	/* Loop through the chips */
> -	for (; chip < nrchips; chip++) {
> -		/*
> -		 * There was already a version of the table, reuse the page
> -		 * This applies for absolute placement too, as we have the
> -		 * page nr. in td->pages.
> -		 */
> -		if (td->pages[chip] != -1) {
> -			page = td->pages[chip];
> -			goto write;
> +	while (chip < nrchips) {

I'm probably missing something, but why are you turning the for loop
into a while loop in this patch? The commit message does not mention
that, and I don't see why you need it before you actually start
reworking the code to recover from BBT write failures (which is done in
patch 2).

> +		int block;
> +
> +		block = get_bbt_block(this, td, md, chip);
> +		if (block < 0) {
> +			pr_err("No space left to write bad block table\n");
> +			res = block;
> +			goto outerr;
>  		}
>  
>  		/*
> -		 * Automatic placement of the bad block table. Search direction
> -		 * top -> down?
> +		 * get_bbt_block() returns a block number, shift the value to
> +		 * get a page number.
>  		 */
> -		if (td->options & NAND_BBT_LASTBLOCK) {
> -			startblock = numblocks * (chip + 1) - 1;
> -			dir = -1;
> -		} else {
> -			startblock = chip * numblocks;
> -			dir = 1;
> -		}
> -
> -		for (i = 0; i < td->maxblocks; i++) {
> -			int block = startblock + dir * i;
> -			/* Check, if the block is bad */
> -			switch (bbt_get_entry(this, block)) {
> -			case BBT_BLOCK_WORN:
> -			case BBT_BLOCK_FACTORY_BAD:
> -				continue;
> -			}
> -			page = block <<
> -				(this->bbt_erase_shift - this->page_shift);
> -			/* Check, if the block is used by the mirror table */
> -			if (!md || md->pages[chip] != page)
> -				goto write;
> -		}
> -		pr_err("No space left to write bad block table\n");
> -		return -ENOSPC;
> -	write:
> +		page = block << (this->bbt_erase_shift - this->page_shift);
>  
>  		/* Set up shift count and masks for the flash table */
>  		bits = td->options & NAND_BBT_NRBITS_MSK;
> @@ -800,7 +838,7 @@ static int write_bbt(struct mtd_info *mtd, uint8_t *buf,
>  			 (unsigned long long)to, td->version[chip]);
>  
>  		/* Mark it as used */
> -		td->pages[chip] = page;
> +		td->pages[chip++] = page;
>  	}
>  	return 0;
>  

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