Date:   Wed, 20 Jun 2018 12:34:01 +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 2018-06-18 17:05, Miquel Raynal wrote:
> Hi Abhishek,
> 
> Boris, one question for you below :)
> 
>> >> >> >>   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.
>> >> > > I see, thanks for pointing this thread.
>> > > Well for now then let's keep our driver-specific implementation.
>> > > I will just ask you to do a consistent check as requested above (you
>> > can copy code from the core) and add a comment above this function
>> > explaining why it is needed (what you just told me).
>> >
>>   Hi Miquel,
>> 
>>   I explored more regarding making custom bad block functions in this
>>   thread and it looks like, we can move to generic block_bad function
>>   by small changes in QCOM NAND driver
>>   only. The main problem was, in read page with ECC, the bad block
>>   byte was skipped.
>> 
>>   But controller is copying the bad block bytes in another register
>>   with following status bytes.
>> 
>>   BAD_BLOCK_STATUS : With every page read operation, when the 
>> controller
>>   reads a page with a bad block, it writes the bad block status data 
>> into
>>   this register.
>> 
>>   We can update the BBM bytes at start of OOB data in read_oob 
>> function
>>   with these status bytes. It will help in getting rid of 
>> driver-specific
>>   implementation for chip->block_bad.
> 
> If think this is acceptable.
> 
>> 
>>   For chip->block_markbad, if we want to get rid of
>>   driver-specific implementation then we can have
>>   following logic
>> 
>>   in write_oob function check for bad block bytes in oob
>>   and do the raw write for updating BBM bytes alone in
>>   flash if BBM bytes are non 0xff.
> 
> Ok but this will have to be properly explained in a descriptive 
> comment!
> 
> Maybe Boris can give its point of view on the subject. Is it worth
> adding the above 'hacks' in the qcom driver and get rid of the
> driver-specific ->is_bad()/->mark_bad() impementations?

  Thanks Miquel.

  I will remove this patch from this patch series and will send
  separate patch series for all bad block handling related changes
  once things are finalized.

  Regards,
  Abhishek

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