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Date:   Mon, 17 Jun 2019 14:35:10 +0200
From:   Miquel Raynal <miquel.raynal@bootlin.com>
To:     masonccyang@mxic.com.tw
Cc:     bbrezillon@kernel.org, broonie@kernel.org,
        christophe.kerello@st.com, computersforpeace@gmail.com,
        devicetree@vger.kernel.org, dwmw2@infradead.org,
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        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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Hi Mason,

masonccyang@mxic.com.tw wrote on Wed, 29 May 2019 11:12:08 +0800:

> 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().  

Most of the chips today are CS-don't-care, which chip are you using?

Is this behavior publicly documented?

Is this LPM mode always activated?

> 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() ?
> 

No, if really needed, we could add a "macro op done" flag in the nand
operation structure.


Thanks,
Miquèl