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To:     "Miquel Raynal" <miquel.raynal@bootlin.com>
Cc:     bbrezillon@kernel.org, broonie@kernel.org,
        christophe.kerello@st.com, computersforpeace@gmail.com,
        devicetree@vger.kernel.org, dwmw2@infradead.org,
        geert@linux-m68k.org, juliensu@mxic.com.tw, lee.jones@linaro.org,
        liang.yang@amlogic.com, linux-kernel@vger.kernel.org,
        linux-mtd@lists.infradead.org, linux-spi@vger.kernel.org,
        marcel.ziswiler@toradex.com, marek.vasut@gmail.com,
        mark.rutland@arm.com, paul.burton@mips.com, richard@nod.at,
        robh+dt@kernel.org, stefan@agner.ch, zhengxunli@mxic.com.tw
Subject: Re: [PATCH v3 2/4] mtd: rawnand: Add Macronix MX25F0A NAND controller
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Message-ID: <OFE923A8E5.50375C30-ON48258409.0009AE1B-48258409.00119767@mxic.com.tw>
From:   masonccyang@mxic.com.tw
Date:   Wed, 29 May 2019 11:12:08 +0800
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Hi Miquel,

> > > > > > +static void mxic_nand_select_chip(struct nand_chip *chip, int 
 
> > chipnr) 
> > > > > 
> > > > > _select_target() is preferred now 
> > > > 
> > > > Do you mean I implement mxic_nand_select_target() to control #CS ?
> > > > 
> > > > If so, I need to call mxic_nand_select_target( ) to control #CS ON
> > > > and then #CS OFF in _exec_op() due to nand_select_target()<in 
> > nand_base,c> 
> > > > is still calling chip->legacy.select_chip ? 
> > > 
> > > You must forget about the ->select_chip() callback. Now it should be
> > > handled directly from the controller driver. Please have a look at 
the
> > > commit pointed against the marvell_nand.c driver. 
> > 
> > I have no Marvell NFC datasheet and have one question.
> > 
> > In marvell_nand.c, there is no xxx_deselect_target() or 
> > something like that doing #CS OFF.
> > marvell_nfc_select_target() seems always to make one of chip or die
> > #CS keep low.
> > 
> > Is it right ?
> 
> Yes, AFAIR there is no "de-assert" mechanism in this controller.
> 
> > 
> > How to make all #CS keep high for NAND to enter 
> > low-power standby mode if driver don't use "legacy.select_chip()" ?
> 
> See commit 02b4a52604a4 ("mtd: rawnand: Make ->select_chip() optional
> when ->exec_op() is implemented") which states:
> 
>         "When [->select_chip() is] not implemented, the core is assuming
>    the CS line is automatically asserted/deasserted by the driver
>    ->exec_op() implementation."
> 
> Of course, the above is right only when the controller driver supports
> the ->exec_op() interface. 

Currently, it seems that we will get the incorrect data and error
operation due to CS in error toggling if CS line is controlled in 
->exec_op().
i.e,. 

1) In nand_onfi_detect() to call nand_exec_op() twice by 
nand_read_param_page_op() and annd_read_data_op()

2) In nand_write_page_xxx to call nand_exec_op() many times by
nand_prog_page_begin_op(), nand_write_data_op() and 
nand_prog_page_end_op().


Should we consider to add a CS line controller in struct nand_controller
i.e,.

struct nand_controller {
         struct mutex lock;
         const struct nand_controller_ops *ops;
+          void (*select_chip)(struct nand_chip *chip, int cs);
};

to replace legacy.select_chip() ?


To patch in nand_select_target() and nand_deselect_target()

void nand_select_target(struct nand_chip *chip, unsigned int cs)
{
        /*
         * cs should always lie between 0 and chip->numchips, when that's 
not
         * the case it's a bug and the caller should be fixed.
         */
        if (WARN_ON(cs > chip->numchips))
                return;

        chip->cur_cs = cs;

+       if (chip->controller->select_chip)
+               chip->controller->select_chip(chip, cs);
+
        if (chip->legacy.select_chip)
                chip->legacy.select_chip(chip, cs);
}

void nand_deselect_target(struct nand_chip *chip)
{
+       if (chip->controller->select_chip)
+               chip->controller->select_chip(chip, -1);
+
        if (chip->legacy.select_chip)
                chip->legacy.select_chip(chip, -1);

        chip->cur_cs = -1;
}


> 
> So if you think it is not too time consuming and worth the trouble to
> assert/deassert the CS at each operation, you may do it in your driver.
> 
> 
> Thanks,
> Miqu?l

thanks & best regards,
Mason

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