Re: [PATCH 4/8] mtd: Add support for emulated SLC mode on MLC NANDs

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Richard,

Richard Weinberger <richard@nod.at> wrote on Thu, 9 Jan 2020 00:49:02
+0100 (CET):

> ----- Ursprüngliche Mail -----
> > Von: "Miquel Raynal" <miquel.raynal@bootlin.com>
> > An: "richard" <richard@nod.at>, "Vignesh Raghavendra" <vigneshr@ti.com>, "Tudor Ambarus" <Tudor.Ambarus@microchip.com>,
> > "linux-mtd" <linux-mtd@lists.infradead.org>
> > CC: "Boris Brezillon" <boris.brezillon@collabora.com>, "Thomas Petazzoni" <thomas.petazzoni@bootlin.com>, "Boris
> > Brezillon" <boris.brezillon@bootlin.com>, "Miquel Raynal" <miquel.raynal@bootlin.com>
> > Gesendet: Montag, 30. Dezember 2019 17:51:25
> > Betreff: [PATCH 4/8] mtd: Add support for emulated SLC mode on MLC NANDs  
> 
> > From: Boris Brezillon <boris.brezillon@bootlin.com>
> > 
> > MLC NANDs can be made a bit more reliable if we only program the lower
> > page of each pair. At least, this solves the paired-pages corruption
> > issue.
> > 
> > Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
> > Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> > ---
> > drivers/mtd/mtdcore.c          | 189 ++++++++++++++++++++++++++++++---
> > drivers/mtd/mtdpart.c          |  54 ++++++----
> > include/linux/mtd/mtd.h        |   7 +-
> > include/linux/mtd/partitions.h |   2 +
> > include/uapi/mtd/mtd-abi.h     |   1 +
> > 5 files changed, 213 insertions(+), 40 deletions(-)
> > 
> > diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
> > index 2916674208b3..de0a692ecb29 100644
> > --- a/drivers/mtd/mtdcore.c
> > +++ b/drivers/mtd/mtdcore.c
> > @@ -617,6 +617,19 @@ int add_mtd_device(struct mtd_info *mtd)
> > 		    !(mtd->flags & MTD_NO_ERASE)))
> > 		return -EINVAL;
> > 
> > +	/*
> > +	 * MTD_MLC_IN_SLC_MODE can only be set on partitions, when the master  
> 
> I suggest giving a name which indicates that we are actually emulating
> an SLC. Maybe MTD_SLC_EMULATION?
> Some MLC NANDs support SLC mode in hardware, MTD_MLC_IN_SLC_MODE reads like
> this feature.

You're right. What about MTD_SLC_ON_MLC_EMULATION?

I like to see that we are manipulating MLC NANDs.

> 
> > +	 * is an MLC NAND and has a proper pairing scheme defined.
> > +	 * We also reject masters that implement ->_writev() for now, because
> > +	 * NAND controller drivers don't implement this hook, and adding the
> > +	 * SLC -> MLC address/length conversion to this path is useless if we
> > +	 * don't have a user.
> > +	 */
> > +	if (mtd->flags & MTD_MLC_IN_SLC_MODE &&
> > +	    (!mtd_is_partition(mtd) || master->type != MTD_MLCNANDFLASH ||
> > +	     !master->pairing || master->_writev))
> > +		return -EINVAL;
> > +
> > 	mutex_lock(&mtd_table_mutex);
> > 
> > 	i = idr_alloc(&mtd_idr, mtd, 0, 0, GFP_KERNEL);
> > @@ -632,6 +645,14 @@ int add_mtd_device(struct mtd_info *mtd)
> > 	if (mtd->bitflip_threshold == 0)
> > 		mtd->bitflip_threshold = mtd->ecc_strength;
> > 
> > +	if (mtd->flags & MTD_MLC_IN_SLC_MODE) {
> > +		int ngroups = mtd_pairing_groups(master);
> > +
> > +		mtd->erasesize /= ngroups;
> > +		mtd->size = (u64)mtd_div_by_eb(mtd->size, master) *
> > +			    mtd->erasesize;  
> 
> Can we please have a helper for this? You use this formula many times.

Absolutely!

> 
> > +	}
> > +
> > 	if (is_power_of_2(mtd->erasesize))
> > 		mtd->erasesize_shift = ffs(mtd->erasesize) - 1;
> > 	else
> > @@ -1074,9 +1095,11 @@ int mtd_erase(struct mtd_info *mtd, struct erase_info
> > *instr)
> > {
> > 	struct mtd_info *master = mtd_get_master(mtd);
> > 	u64 mst_ofs = mtd_get_master_ofs(mtd, 0);
> > +	struct erase_info adjinstr;
> > 	int ret;
> > 
> > 	instr->fail_addr = MTD_FAIL_ADDR_UNKNOWN;
> > +	adjinstr = *instr;
> > 
> > 	if (!mtd->erasesize || !master->_erase)
> > 		return -ENOTSUPP;
> > @@ -1091,12 +1114,27 @@ int mtd_erase(struct mtd_info *mtd, struct erase_info
> > *instr)
> > 
> > 	ledtrig_mtd_activity();
> > 
> > -	instr->addr += mst_ofs;
> > -	ret = master->_erase(master, instr);
> > -	if (instr->fail_addr != MTD_FAIL_ADDR_UNKNOWN)
> > -		instr->fail_addr -= mst_ofs;
> > +	if (mtd->flags & MTD_MLC_IN_SLC_MODE) {
> > +		adjinstr.addr = (loff_t)mtd_div_by_eb(instr->addr, mtd) *
> > +				master->erasesize;
> > +		adjinstr.len = ((u64)mtd_div_by_eb(instr->addr + instr->len, mtd) *
> > +				master->erasesize) -
> > +			       adjinstr.addr;
> > +	}
> > +
> > +	adjinstr.addr += mst_ofs;
> > +
> > +	ret = master->_erase(master, &adjinstr);
> > +
> > +	if (adjinstr.fail_addr != MTD_FAIL_ADDR_UNKNOWN) {
> > +		instr->fail_addr = adjinstr.fail_addr - mst_ofs;
> > +		if (mtd->flags & MTD_MLC_IN_SLC_MODE) {
> > +			instr->fail_addr = mtd_div_by_eb(instr->fail_addr,
> > +							 master);
> > +			instr->fail_addr *= mtd->erasesize;
> > +		}
> > +	}
> > 
> > -	instr->addr -= mst_ofs;
> > 	return ret;
> > }
> > EXPORT_SYMBOL_GPL(mtd_erase);
> > @@ -1276,6 +1314,101 @@ static int mtd_check_oob_ops(struct mtd_info *mtd,
> > loff_t offs,
> > 	return 0;
> > }
> > 
> > +static int mtd_read_oob_std(struct mtd_info *mtd, loff_t from,
> > +			    struct mtd_oob_ops *ops)
> > +{
> > +	struct mtd_info *master = mtd_get_master(mtd);
> > +	int ret;
> > +
> > +	from = mtd_get_master_ofs(mtd, from);
> > +	if (master->_read_oob)
> > +		ret = master->_read_oob(master, from, ops);
> > +	else
> > +		ret = master->_read(master, from, ops->len, &ops->retlen,
> > +				    ops->datbuf);
> > +
> > +	return ret;
> > +}
> > +
> > +static int mtd_write_oob_std(struct mtd_info *mtd, loff_t to,
> > +			     struct mtd_oob_ops *ops)
> > +{
> > +	struct mtd_info *master = mtd_get_master(mtd);
> > +	int ret;
> > +
> > +	to = mtd_get_master_ofs(mtd, to);
> > +	if (master->_write_oob)
> > +		ret = master->_write_oob(master, to, ops);
> > +	else
> > +		ret = master->_write(master, to, ops->len, &ops->retlen,
> > +				     ops->datbuf);
> > +
> > +	return ret;
> > +}
> > +
> > +static int mtd_oob_io_slc(struct mtd_info *mtd, loff_t start, bool read,
> > +			  struct mtd_oob_ops *ops)  
> 
> The name is misleading. We don't do OOB IO on a SLC NAND,
> we emulate SLC.

What would you recommend? mtd_oob_io_emul_slc?

> 
> Thanks,
> //richard

Thanks,
Miquèl

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