linux-kernel - Re: [PATCH RFC 3/3] mtd: rawnand: Add support Macronix power down mode

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Date:   Tue, 8 Oct 2019 10:06:50 +0800
From:   masonccyang@...c.com.tw
To:     "Miquel Raynal" <miquel.raynal@...tlin.com>
Cc:     bbrezillon@...nel.org, computersforpeace@...il.com,
        dwmw2@...radead.org, frieder.schrempf@...tron.de,
        gregkh@...uxfoundation.org, juliensu@...c.com.tw,
        linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org,
        marcel.ziswiler@...adex.com, marek.vasut@...il.com, richard@....at,
        tglx@...utronix.de, vigneshr@...com
Subject: Re: [PATCH RFC 3/3] mtd: rawnand: Add support Macronix power down mode

Hi Miquel,

> > +int nand_power_down_op(struct nand_chip *chip)
> > +{
> > +   int ret;
> > +
> > +   if (nand_has_exec_op(chip)) {
> > +      struct nand_op_instr instrs[] = {
> > +         NAND_OP_CMD(NAND_CMD_POWER_DOWN, 0),
> > +      };
> > +
> > +      struct nand_operation op = NAND_OPERATION(chip->cur_cs, 
instrs);
> > +
> > +      ret = nand_exec_op(chip, &op);
> > +      if (ret)
> > +         return ret;
> > +
> > +   } else {
> > +      chip->legacy.cmdfunc(chip, NAND_CMD_POWER_DOWN, -1, -1);
> > +   }
> > +
> > +   return 0;
> > +}
> > +
> > +static int mxic_nand_suspend(struct mtd_info *mtd)
> > +{
> > +   struct nand_chip *chip = mtd_to_nand(mtd);
> > +
> > +   mutex_lock(&chip->lock);
> > +
> > +   nand_select_target(chip, 0);
> > +   nand_power_down_op(chip);
> > +   nand_deselect_target(chip);
> > +
> > +   chip->suspend = 1;
> > +   mutex_unlock(&chip->lock);
> > +
> > +   return 0;
> > +}
> > +
> > +static void mxic_nand_resume(struct mtd_info *mtd)
> > +{
> > +   struct nand_chip *chip = mtd_to_nand(mtd);
> > +
> > +   mutex_lock(&chip->lock);
> > +   // toggle #CS pin to resume NAND device
> 
> C++ style comments are forbidden in code.

okay, got it. thanks.

> 
> > +   nand_select_target(chip, 0);
> 
> On several NAND controllers there is no way to act on the CS line
> without actually writing bytes to the NAND chip. So basically this
> is very likely to not work.

any other way to make it work ? GPIO ?
or just have some comments description here.
i.e,.

/* The NAND chip will exit the deep power down mode with #CS toggling, 
 * please refer to datasheet for the timing requirement of tCRDP and tRDP.
 */

> 
> > +   ndelay(20);
> 
> Is this delay known somewhere? Is this purely experimental?

it's timing requirement tCRDP 20 ns(min) to release device
from deep power-down mode. 
You may download datasheet at
https://www.macronix.com/zh-tw/products/NAND-Flash/SLC-NAND-Flash/Pages/spec.aspx?p=MX30LF4G28AD&m=SLC%20NAND&n=PM2579 

> 
> > +   nand_deselect_target(chip);
> > +
> > +   if (chip->suspend)
> > +      chip->suspended = 0;
> > +   else
> > +      pr_err("%s call for a chip which is not in suspended state\n",
> > +             __func__);
> > +   mutex_unlock(&chip->lock);
> > +}

thanks & best regards,
Mason

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