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

[Arseniy Krasnov]

On 04.07.2023 12:41, Miquel Raynal wrote:
> Hi Arseniy,
> 
> avkrasnov@xxxxxxxxxxxxxx wrote on Tue, 4 Jul 2023 12:23:03 +0300:
> 
>> On 04.07.2023 11:36, Miquel Raynal wrote:
>>> Hi Arseniy,
>>>
>>> AVKrasnov@xxxxxxxxxxxxxx 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@xxxxxxxxxxxxxx>
>>>> ---
>>>>  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.

Hm I checked, that but if step size is not set in DTS, here it will be 0, 
then it will be selected in 'nand_ecc_choose_conf()' according provided 'ecc_caps'
and 'oobavail'...

Anyway, I'll do the following thing:

int nsectors;

if (nand->ecc.size)
    nsectors = mtd->writesize / nand->ecc.size; <--- this is for 512 ECC
else
    nsectors = mtd->writesize / 1024; <--- this is for default 1024 ECC

Thanks, Arseniy

> 
>>
>> 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