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

[Abhishek Sahu]

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