linux-kernel - Re: [RFC PATCH v1 2/2] mtd: rawnand: meson: support for 512B ECC step size

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Message-ID: <20230704114110.25ca9de4@xps-13>
Date:   Tue, 4 Jul 2023 11:41:10 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Arseniy Krasnov <avkrasnov@...rdevices.ru>
Cc:     Liang Yang <liang.yang@...ogic.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Kevin Hilman <khilman@...libre.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        <oxffffaa@...il.com>, <kernel@...rdevices.ru>,
        <linux-mtd@...ts.infradead.org>, <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-amlogic@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v1 2/2] mtd: rawnand: meson: support for 512B ECC
 step size

Hi Arseniy,

avkrasnov@...rdevices.ru wrote on Tue, 4 Jul 2023 12:23:03 +0300:

> On 04.07.2023 11:36, Miquel Raynal wrote:
> > Hi Arseniy,
> > 
> > AVKrasnov@...rdevices.ru wrote on Wed, 28 Jun 2023 12:29:36 +0300:
> >   
> >> Meson NAND supports both 512B and 1024B ECC step size.
> >>
> >> Signed-off-by: Arseniy Krasnov <AVKrasnov@...rdevices.ru>
> >> ---
> >>  drivers/mtd/nand/raw/meson_nand.c | 47 +++++++++++++++++++++++--------
> >>  1 file changed, 35 insertions(+), 12 deletions(-)
> >>
> >> diff --git a/drivers/mtd/nand/raw/meson_nand.c b/drivers/mtd/nand/raw/meson_nand.c
> >> index 345212e8c691..6cc4f63b86c8 100644
> >> --- a/drivers/mtd/nand/raw/meson_nand.c
> >> +++ b/drivers/mtd/nand/raw/meson_nand.c
> >> @@ -135,6 +135,7 @@ struct meson_nfc_nand_chip {
> >>  struct meson_nand_ecc {
> >>  	u32 bch;
> >>  	u32 strength;
> >> +	u32 size;
> >>  };
> >>  
> >>  struct meson_nfc_data {
> >> @@ -190,7 +191,8 @@ struct meson_nfc {
> >>  };
> >>  
> >>  enum {
> >> -	NFC_ECC_BCH8_1K		= 2,
> >> +	NFC_ECC_BCH8_512	= 1,
> >> +	NFC_ECC_BCH8_1K,
> >>  	NFC_ECC_BCH24_1K,
> >>  	NFC_ECC_BCH30_1K,
> >>  	NFC_ECC_BCH40_1K,
> >> @@ -198,15 +200,16 @@ enum {
> >>  	NFC_ECC_BCH60_1K,
> >>  };
> >>  
> >> -#define MESON_ECC_DATA(b, s)	{ .bch = (b),	.strength = (s)}
> >> +#define MESON_ECC_DATA(b, s, sz)	{ .bch = (b), .strength = (s), .size = (sz) }
> >>  
> >>  static struct meson_nand_ecc meson_ecc[] = {
> >> -	MESON_ECC_DATA(NFC_ECC_BCH8_1K, 8),
> >> -	MESON_ECC_DATA(NFC_ECC_BCH24_1K, 24),
> >> -	MESON_ECC_DATA(NFC_ECC_BCH30_1K, 30),
> >> -	MESON_ECC_DATA(NFC_ECC_BCH40_1K, 40),
> >> -	MESON_ECC_DATA(NFC_ECC_BCH50_1K, 50),
> >> -	MESON_ECC_DATA(NFC_ECC_BCH60_1K, 60),
> >> +	MESON_ECC_DATA(NFC_ECC_BCH8_512, 8,  512),
> >> +	MESON_ECC_DATA(NFC_ECC_BCH8_1K,  8,  1024),
> >> +	MESON_ECC_DATA(NFC_ECC_BCH24_1K, 24, 1024),
> >> +	MESON_ECC_DATA(NFC_ECC_BCH30_1K, 30, 1024),
> >> +	MESON_ECC_DATA(NFC_ECC_BCH40_1K, 40, 1024),
> >> +	MESON_ECC_DATA(NFC_ECC_BCH50_1K, 50, 1024),
> >> +	MESON_ECC_DATA(NFC_ECC_BCH60_1K, 60, 1024),
> >>  };
> >>  
> >>  static int meson_nand_calc_ecc_bytes(int step_size, int strength)
> >> @@ -224,8 +227,27 @@ static int meson_nand_calc_ecc_bytes(int step_size, int strength)
> >>  
> >>  NAND_ECC_CAPS_SINGLE(meson_gxl_ecc_caps,
> >>  		     meson_nand_calc_ecc_bytes, 1024, 8, 24, 30, 40, 50, 60);
> >> -NAND_ECC_CAPS_SINGLE(meson_axg_ecc_caps,
> >> -		     meson_nand_calc_ecc_bytes, 1024, 8);
> >> +
> >> +static const int axg_stepinfo_strengths[] = { 8 };
> >> +static const struct nand_ecc_step_info axg_stepinfo_1024 = {
> >> +	.stepsize = 1024,
> >> +	.strengths = axg_stepinfo_strengths,
> >> +	.nstrengths = ARRAY_SIZE(axg_stepinfo_strengths)
> >> +};
> >> +
> >> +static const struct nand_ecc_step_info axg_stepinfo_512 = {
> >> +	.stepsize = 512,
> >> +	.strengths = axg_stepinfo_strengths,
> >> +	.nstrengths = ARRAY_SIZE(axg_stepinfo_strengths)
> >> +};
> >> +
> >> +static const struct nand_ecc_step_info axg_stepinfo[] = { axg_stepinfo_1024, axg_stepinfo_512 };
> >> +
> >> +static const struct nand_ecc_caps meson_axg_ecc_caps = {
> >> +	.stepinfos = axg_stepinfo,
> >> +	.nstepinfos = ARRAY_SIZE(axg_stepinfo),
> >> +	.calc_ecc_bytes = meson_nand_calc_ecc_bytes,
> >> +};
> >>  
> >>  static struct meson_nfc_nand_chip *to_meson_nand(struct nand_chip *nand)
> >>  {
> >> @@ -1259,7 +1281,8 @@ static int meson_nand_bch_mode(struct nand_chip *nand)
> >>  		return -EINVAL;
> >>  
> >>  	for (i = 0; i < ARRAY_SIZE(meson_ecc); i++) {
> >> -		if (meson_ecc[i].strength == nand->ecc.strength) {
> >> +		if (meson_ecc[i].strength == nand->ecc.strength &&
> >> +		    meson_ecc[i].size == nand->ecc.size) {
> >>  			meson_chip->bch_mode = meson_ecc[i].bch;
> >>  			return 0;
> >>  		}
> >> @@ -1278,7 +1301,7 @@ static int meson_nand_attach_chip(struct nand_chip *nand)
> >>  	struct meson_nfc *nfc = nand_get_controller_data(nand);
> >>  	struct meson_nfc_nand_chip *meson_chip = to_meson_nand(nand);
> >>  	struct mtd_info *mtd = nand_to_mtd(nand);
> >> -	int nsectors = mtd->writesize / 1024;
> >> +	int nsectors = mtd->writesize / 512;  
> > 
> > This cannot be unconditional, right?  
> 
> Hello Miquel!
> 
> Yes, this code looks strange. 'nsectors' is used to calculate space in OOB
> that could be used by ECC engine (this value will be passed as 'oobavail'
> to 'nand_ecc_choose_conf()'). Idea of 512 is to consider "worst" case
> for ECC, e.g. minimal number of bytes for ECC engine (and at the same time
> maximum number of free bytes). For Meson, if ECC step size is 512, then we
> have 4 x 2 free bytes in OOB (if step size if 1024 then we have 2 x 2 free
> bytes in OOB).
> 
> I think this code could be reworked in the following way:
> 
> if ECC step size is already known here (from DTS), calculate 'nsectors' using
> given value (div by 512 for example). Otherwise calculate 'nsectors' in the
> current manner:

It will always be known when these function are run. There is no
guessing here.

> 
> int nsectors = mtd->writesize / 1024;
> 
> Moreover 1024 is default ECC step size for this driver, so default behaviour
> will be preserved.

Yes, otherwise you would break existing users.

> 
> Thanks, Arseniy
> 
> >   
> >>  	int raw_writesize;
> >>  	int ret;
> >>    
> > 
> > 
> > Thanks,
> > Miquèl  


Thanks,
Miquèl