linux-kernel - Re: [PATCH v3 13/16] mtd: rawnand: qcom: minor code reorganization for bad block check

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Date:   Mon, 28 May 2018 15:40:52 +0530
From:   Abhishek Sahu <absahu@...eaurora.org>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Boris Brezillon <boris.brezillon@...tlin.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mtd@...ts.infradead.org, Andy Gross <andy.gross@...aro.org>,
        Archit Taneja <architt@...eaurora.org>
Subject: Re: [PATCH v3 13/16] mtd: rawnand: qcom: minor code reorganization
 for bad block check

On 2018-05-28 12:33, Miquel Raynal wrote:
> Hi Abhishek,
> 
>> >>  /* implements ecc->read_page() */
>> >>  static int qcom_nandc_read_page(struct mtd_info *mtd, struct >> nand_chip *chip,
>> >>  				uint8_t *buf, int oob_required, int page)
>> >> @@ -2118,6 +2083,7 @@ static int qcom_nandc_block_bad(struct mtd_info >> *mtd, loff_t ofs)
>> >>  	struct nand_ecc_ctrl *ecc = &chip->ecc;
>> >>  	int page, ret, bbpos, bad = 0;
>> >>  	u32 flash_status;
>> >> +	u8 *bbm_bytes_buf = chip->data_buf;
>> >> >>  	page = (int)(ofs >> chip->page_shift) & chip->pagemask;
>> >> >> @@ -2128,11 +2094,31 @@ static int qcom_nandc_block_bad(struct >> mtd_info *mtd, loff_t ofs)
>> >>  	 * that contains the BBM
>> >>  	 */
>> >>  	host->use_ecc = false;
>> >> +	bbpos = mtd->writesize - host->cw_size * (ecc->steps - 1);
>> > > Are we sure there is no layout with only 1 step?
>> 
>>   All the layouts are such that, the BBM will come in
>>   first byte of spare area.
>> 
>>   For 4 bit ECC, the cw_size is 528 so for 2K page
>> 
>>    2048 - 528 * 3 = 464
> 
> My question was more about small page NANDs. But I suppose it works
> too if ecc->steps == 1.
> 

  Correct Miquel.

>> 
>>   So for last CW, the 464 is BBM (i.e 2048th byte) in
>>   full page.
>> 
>> > >> >>  	clear_bam_transaction(nandc);
>> >> -	ret = copy_last_cw(host, page);
>> >> -	if (ret)
>> >> +	clear_read_regs(nandc);
>> >> +
>> >> +	set_address(host, host->cw_size * (ecc->steps - 1), page);
>> >> +	update_rw_regs(host, 1, true);
>> >> +
>> >> +	/*
>> >> +	 * The last codeword data will be copied from NAND device to NAND
>> >> +	 * controller internal HW buffer. Copy only required BBM size bytes
>> >> +	 * from this HW buffer to bbm_bytes_buf which is present at
>> >> +	 * bbpos offset.
>> >> +	 */
>> >> +	nandc_set_read_loc(nandc, 0, bbpos, host->bbm_size, 1);
>> >> +	config_nand_single_cw_page_read(nandc);
>> >> +	read_data_dma(nandc, FLASH_BUF_ACC + bbpos, bbm_bytes_buf,
>> >> +		      host->bbm_size, 0);
>> >> +
>> >> +	ret = submit_descs(nandc);
>> >> +	free_descs(nandc);
>> >> +	if (ret) {
>> >> +		dev_err(nandc->dev, "failed to copy bad block bytes\n");
>> >>  		goto err;
>> >> +	}
>> >> >>  	flash_status = le32_to_cpu(nandc->reg_read_buf[0]);
>> >> >> @@ -2141,12 +2127,10 @@ static int qcom_nandc_block_bad(struct >> mtd_info *mtd, loff_t ofs)
>> >>  		goto err;
>> >>  	}
>> >> >> -	bbpos = mtd->writesize - host->cw_size * (ecc->steps - 1);
>> >> -
>> >> -	bad = nandc->data_buffer[bbpos] != 0xff;
>> >> +	bad = bbm_bytes_buf[0] != 0xff;
>> > > This is suspect as it still points to the beginning of the data buffer.
>> > Can you please check you did not meant bbm_bytes_buf[bbpos]?
>> >
>>   The main thing here is
>>   nandc_set_read_loc(nandc, 0, bbpos, host->bbm_size, 1);
>> 
>>   After reading one complete CW from NAND, the data will be still
>>   in NAND HW buffer.
>> 
>>   The above register tells that we need to read data from
>>   bbpos of size host->bbm_size (which is 1 byte for 8 bus witdh
>>   and 2 byte for 16 bus width) in bbm_bytes_buf.
> 
> I see: idx 0 in bbm_bytes_buf is the data at offset bbpos. Then
> it's ok.
> 
>> 
>>   So bbm_bytes_buf[0] will contain the BBM first byte.
>>   and bbm_bytes_buf[1] will contain the BBM second byte.
>> 
>>   Regards,
>>   Abhishek
>> 
>> >> >>  	if (chip->options & NAND_BUSWIDTH_16)
>> >> -		bad = bad || (nandc->data_buffer[bbpos + 1] != 0xff);
>> >> +		bad = bad || (bbm_bytes_buf[1] != 0xff);
> 
> Sorry, my mistake, I did not see the above line.
> 
> However, technically, the BBM could be located in the first, second or
> last page of the block. You should check the three of them are 0xFF
> before declaring the block is not bad.
> 
> The more I look at the function, the more I wonder if you actually need
> it. Why does the generic nand_block_bad() implementation in the core
> do not fit?

  The BBM bytes can be accessed in raw mode only for QCOM NAND
  Contoller. We started with following patch for initial patches

  http://patchwork.ozlabs.org/patch/508565/

  I am also not very much sure, how can we go ahead now.
  Ideally we need to use generic function only which
  requires raw_read.

  Thanks,
  Abhishek