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Subject: Re: [PATCH] mtd: rawnand: stm32_fmc2: fix broken ECC
To:     Miquel Raynal <miquel.raynal@bootlin.com>
CC:     <richard@nod.at>, <vigneshr@ti.com>,
        <linux-mtd@lists.infradead.org>, <linux-kernel@vger.kernel.org>,
        <linux-stm32@st-md-mailman.stormreply.com>
References: <1603989492-6670-1-git-send-email-christophe.kerello@st.com>
 <20201030091905.111aa7a4@xps13>
From:   Christophe Kerello <christophe.kerello@st.com>
Message-ID: <d3073938-e714-6b5d-1dc9-36887b11de46@st.com>
Date:   Fri, 30 Oct 2020 09:31:25 +0100
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Hi Miquel,

On 10/30/20 9:19 AM, Miquel Raynal wrote:
> Hi Christophe,
> 
> Christophe Kerello <christophe.kerello@st.com> wrote on Thu, 29 Oct
> 2020 17:38:12 +0100:
> 
>> Since commit d7157ff49a5b ("mtd: rawnand: Use the ECC framework user
>> input parsing bits"), ECC are broken in FMC2 driver in case of
>> nand-ecc-step-size and nand-ecc-strength are not set in the device tree.
>> The default user configuration set in FMC2 driver is lost when
>> rawnand_dt_init function is called. To avoid to lose the default user
>> configuration, it is needed to move it in the new user_conf structure.
>>
>> Signed-off-by: Christophe Kerello <christophe.kerello@st.com>
>> Fixes: d7157ff49a5b ("mtd: rawnand: Use the ECC framework user input parsing bits")
>> ---
>>   drivers/mtd/nand/raw/stm32_fmc2_nand.c | 8 +++++---
>>   1 file changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/mtd/nand/raw/stm32_fmc2_nand.c b/drivers/mtd/nand/raw/stm32_fmc2_nand.c
>> index b31a581..dc86ac9 100644
>> --- a/drivers/mtd/nand/raw/stm32_fmc2_nand.c
>> +++ b/drivers/mtd/nand/raw/stm32_fmc2_nand.c
>> @@ -1846,6 +1846,7 @@ static int stm32_fmc2_nfc_probe(struct platform_device *pdev)
>>   	struct resource *res;
>>   	struct mtd_info *mtd;
>>   	struct nand_chip *chip;
>> +	struct nand_device *nanddev;
>>   	struct resource cres;
>>   	int chip_cs, mem_region, ret, irq;
>>   	int start_region = 0;
>> @@ -1952,10 +1953,11 @@ static int stm32_fmc2_nfc_probe(struct platform_device *pdev)
>>   	chip->options |= NAND_BUSWIDTH_AUTO | NAND_NO_SUBPAGE_WRITE |
>>   			 NAND_USES_DMA;
>>   
>> -	/* Default ECC settings */
>> +	/* Default ECC user settings */
>>   	chip->ecc.engine_type = NAND_ECC_ENGINE_TYPE_ON_HOST;
>> -	chip->ecc.size = FMC2_ECC_STEP_SIZE;
>> -	chip->ecc.strength = FMC2_ECC_BCH8;
>> +	nanddev = mtd_to_nanddev(mtd);
>> +	nanddev->ecc.user_conf.step_size = FMC2_ECC_STEP_SIZE;
>> +	nanddev->ecc.user_conf.strength = FMC2_ECC_BCH8;
>>   
>>   	/* Scan to find existence of the device */
>>   	ret = nand_scan(chip, nand->ncs);
> 
> Sorry for breaking the driver with this change, but now I think we
> should have all ECC related bits in ->attach() instead of ->probe().
> The ->attach() hook is called during the nand_scan() operation and at
> this point the chip's requirements/layout are known (not before). I
> know that certain controllers don't really care about that, here your
> simply hardcode these two fields and you don't need to know anything
> about the chip's properties. But as a bid to harmonize all drivers with
> the target of a generic ECC engine in mind, I think it's now time to
> move these three lines (chip->ecc.* = ...) at the top of ->attach().
> Also, these fields should have been populated by the core so perhaps
> the best approach is to check if the user requirements are synced with
> the controller's capabilities and error out otherwise?
> 
> We plan to send a fixes PR for -rc2, if the v2 arrives today I'll
> integrate it.

Ok. Issue is that the controller is initialized when 
stm32_fmc2_nfc_select_chip is called. This function will be called 
before the ->attach() hook, when the first command will be sent to the 
NAND device (reset command). So, moving the default ECC initialization
needs probably more modifications in the driver.
I will try to send a v2 today.

Regards,
Christophe Kerello.

> 
> Thanks,
> Miquèl
>