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Message-ID: <cc0e98e4-b92f-4da5-879d-7535e787b98f@broadcom.com>
Date: Thu, 22 Feb 2024 19:35:12 -0800
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Subject: Re: [PATCH v5 09/12] mtd: rawnand: brcmnand: Add support for getting
 ecc setting from strap
To: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Linux MTD List <linux-mtd@lists.infradead.org>,
 Linux ARM List <linux-arm-kernel@lists.infradead.org>,
 Broadcom Kernel List <bcm-kernel-feedback-list@broadcom.com>,
 f.fainelli@gmail.com, kursad.oney@broadcom.com, joel.peshkin@broadcom.com,
 anand.gore@broadcom.com, dregan@mail.com, kamal.dasu@broadcom.com,
 tomer.yacoby@broadcom.com, dan.beygelman@broadcom.com,
 David Regan <dregan@broadcom.com>, linux-kernel@vger.kernel.org,
 Vignesh Raghavendra <vigneshr@ti.com>,
 Brian Norris <computersforpeace@gmail.com>,
 Richard Weinberger <richard@nod.at>
References: <20240207202257.271784-1-william.zhang@broadcom.com>
 <20240207202257.271784-10-william.zhang@broadcom.com>
 <20240220105313.5e3c600d@xps-13>
From: William Zhang <william.zhang@broadcom.com>
In-Reply-To: <20240220105313.5e3c600d@xps-13>
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Hi Miquel,

On 2/20/24 01:53, Miquel Raynal wrote:
> Hi William,
> 
> william.zhang@broadcom.com wrote on Wed,  7 Feb 2024 12:22:54 -0800:
> 
>> BCMBCA broadband SoC based board design does not specify ecc setting in
>> dts but rather use the SoC NAND strap info to obtain the ecc strength
>> and spare area size setting. Add brcm,nand-ecc-use-strap dts propety for
>> this purpose and update driver to support this option.
>>
>> The generic nand ecc settings still take precedence over this flag. For
>> example, if nand-ecc-strength is set in the dts, the driver ignores the
>> strap setting and falls back to original behavior. This makes sure that
>> the existing BCMBCA board dts still works the old way even the strap
>> flag is set in the BCMBCA chip dtsi.
>>
>> Signed-off-by: William Zhang <william.zhang@broadcom.com>
>> Reviewed-by: David Regan <dregan@broadcom.com>
>>
>> ---
>>
>> Changes in v5: None
>> Changes in v4:
>> - Update the comments for ecc setting selection
>>
>> Changes in v3: None
>> Changes in v2:
>> - Minor cosmetic fixes
>>
>>   drivers/mtd/nand/raw/brcmnand/brcmnand.c | 83 ++++++++++++++++++++++--
>>   1 file changed, 76 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/mtd/nand/raw/brcmnand/brcmnand.c b/drivers/mtd/nand/raw/brcmnand/brcmnand.c
>> index 73fdf7ce21aa..efeee9e80213 100644
>> --- a/drivers/mtd/nand/raw/brcmnand/brcmnand.c
>> +++ b/drivers/mtd/nand/raw/brcmnand/brcmnand.c
>> @@ -1038,6 +1038,19 @@ static inline int brcmnand_sector_1k_shift(struct brcmnand_controller *ctrl)
>>   		return -1;
>>   }
>>   
>> +static int brcmnand_get_sector_size_1k(struct brcmnand_host *host)
>> +{
>> +	struct brcmnand_controller *ctrl = host->ctrl;
>> +	int shift = brcmnand_sector_1k_shift(ctrl);
>> +	u16 acc_control_offs = brcmnand_cs_offset(ctrl, host->cs,
>> +						  BRCMNAND_CS_ACC_CONTROL);
>> +
>> +	if (shift < 0)
>> +		return 0;
>> +
>> +	return (nand_readreg(ctrl, acc_control_offs) >> shift) & 0x1;
> 
> What is this & 0x1 ? If you return a yes/no value, please make this
> function return a bool. Also, please use intermediate steps to clarify
> what you do.
> 
> sector_1k_bit = ...;
> acc = nand_readreg();
> return acc & BIT(sector_1k_bit);
> 
> Or something like that.
> 
This sector 1k bit is just single bit field. But we do want to return 
negative for error condition and 0 for 512 sector and 1 for 1K sector 
size. Will add intermediate steps.

>> +}
>> +
>>   static void brcmnand_set_sector_size_1k(struct brcmnand_host *host, int val)
>>   {
>>   	struct brcmnand_controller *ctrl = host->ctrl;
>> @@ -1055,6 +1068,38 @@ static void brcmnand_set_sector_size_1k(struct brcmnand_host *host, int val)
>>   	nand_writereg(ctrl, acc_control_offs, tmp);
>>   }
>>   
>> +static int brcmnand_get_spare_size(struct brcmnand_host *host)
>> +{
>> +	struct brcmnand_controller *ctrl = host->ctrl;
>> +	u16 acc_control_offs = brcmnand_cs_offset(ctrl, host->cs,
>> +						  BRCMNAND_CS_ACC_CONTROL);
>> +	u32 acc = nand_readreg(ctrl, acc_control_offs);
>> +
>> +	return (acc & brcmnand_spare_area_mask(ctrl));
>> +}
>> +
>> +static int brcmnand_get_ecc_strength(struct brcmnand_host *host)
> 
> 					_from_strap
> 
>> +{
>> +	struct brcmnand_controller *ctrl = host->ctrl;
>> +	u16 acc_control_offs = brcmnand_cs_offset(ctrl, host->cs,
>> +						  BRCMNAND_CS_ACC_CONTROL);
>> +	int sector_size_1k = brcmnand_get_sector_size_1k(host);
>> +	int spare_area_size, ecc_level, ecc_strength;
>> +	u32 acc;
>> +
>> +	spare_area_size = brcmnand_get_spare_size(host);
>> +	acc = nand_readreg(ctrl, acc_control_offs);
>> +	ecc_level = (acc & brcmnand_ecc_level_mask(ctrl)) >> ctrl->ecc_level_shift;
> 
> Please use FIELD_PREP/FIELD_GET.
> 
These macros do not work here as the mask is not constant.

>> +	if (sector_size_1k)
>> +		ecc_strength = ecc_level * 2;
>> +	else if (spare_area_size == 16 && ecc_level == 15)
>> +		ecc_strength = 1; /* hamming */
>> +	else
>> +		ecc_strength = ecc_level;
>> +
>> +	return ecc_strength;
>> +}
>> +
>>   /***********************************************************************
>>    * CS_NAND_SELECT
>>    ***********************************************************************/
>> @@ -2622,19 +2667,43 @@ static int brcmnand_setup_dev(struct brcmnand_host *host)
>>   		nanddev_get_memorg(&chip->base);
>>   	struct brcmnand_controller *ctrl = host->ctrl;
>>   	struct brcmnand_cfg *cfg = &host->hwcfg;
>> -	char msg[128];
>> +	struct device_node *np = nand_get_flash_node(chip);
>>   	u32 offs, tmp, oob_sector;
>> -	int ret;
>> +	int ret, sector_size_1k = 0;
>> +	bool use_strap = false;
>> +	char msg[128];
>>   
>>   	memset(cfg, 0, sizeof(*cfg));
>> +	use_strap = of_property_read_bool(np, "brcm,nand-ecc-use-strap");
>>   
>> -	ret = of_property_read_u32(nand_get_flash_node(chip),
>> -				   "brcm,nand-oob-sector-size",
>> +	/*
>> +	 * Set ECC size and strength based on hw configuration from strap
>> +	 * if brcm,nand-ecc-use-strap is set. However if nand-ecc-strength
>> +	 * is set, its value will be used and ignore the strap setting.
> 
> Please error out in this case. It's one or the other, not both.
> 
Will update.

>> +	 */
>> +	if (chip->ecc.strength)
>> +		use_strap = 0;
>> +
>> +	if (use_strap) {
>> +		chip->ecc.strength = brcmnand_get_ecc_strength(host);
>> +		sector_size_1k = brcmnand_get_sector_size_1k(host);
>> +		if (chip->ecc.size == 0) {
>> +			if (sector_size_1k < 0)
>> +				chip->ecc.size = 512;
>> +			else
>> +				chip->ecc.size = 512 << sector_size_1k;
>> +		}
> 
> I'd instead make a function named brcmnand_get_ecc_settings() with the
> chip->ecc parameter, so you can directly fill the entries without
> getting another time the sector_size_1k thing.
> 
> Strength and step size are tightly linked, it does make sense to derive
> them both at the same time.
> 
Will update.

>> +	}
>> +
>> +	ret = of_property_read_u32(np, "brcm,nand-oob-sector-size",
>>   				   &oob_sector);
>>   	if (ret) {
>> -		/* Use detected size */
>> -		cfg->spare_area_size = mtd->oobsize /
>> -					(mtd->writesize >> FC_SHIFT);
>> +		if (use_strap)
>> +			cfg->spare_area_size = brcmnand_get_spare_size(host);
>> +		else
>> +			/* Use detected size */
>> +			cfg->spare_area_size = mtd->oobsize /
>> +						(mtd->writesize >> FC_SHIFT);
>>   	} else {
>>   		cfg->spare_area_size = oob_sector;
>>   	}
> 
> 
> Thanks,
> Miquèl

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