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Date:   Wed, 19 Jun 2019 10:09:04 +0200
From:   Miquel Raynal <miquel.raynal@bootlin.com>
To:     masonccyang@mxic.com.tw
Cc:     "Boris Brezillon" <boris.brezillon@collabora.com>,
        bbrezillon@kernel.org, broonie@kernel.org,
        christophe.kerello@st.com, computersforpeace@gmail.com,
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        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, 19 Jun 2019 16:04:43 +0800:

> Hi Boris,
> 
> > 
> > Re: [PATCH v3 2/4] mtd: rawnand: Add Macronix MX25F0A NAND controller
> > 
> > On Tue, 18 Jun 2019 08:14:36 +0200
> > Boris Brezillon <boris.brezillon@collabora.com> wrote:
> >   
> > > > > > > > 
> > > > > > > > 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().   
> > 
> > Oh, and please provide the modifications you added on top of this patch.
> > Right now we're speculating on what you've done which is definitely not
> > an efficient way to debug this sort of issues.  
> 

We really need to see the datasheet of the NAND chip which has a
problem and how this LPM mode is advertized to understand what the
chip expects and eventually how to work-around it.

> The patch is to add in beginning of ->exec_op() to control CS# low and 
> before return from ->exec_op() to control CS# High.
> i.e,.
> static in mxic_nand_exec_op( )
> {
>  cs_to_low();
> 
> 
> 
>  cs_to_high();
>  return;
> }
> 
> But for nand_onfi_detect(), 
> it calls nand_read_param_page_op() and then nand_read_data_op().
> mxic_nand_exec_op() be called twice for nand_onfi_detect()

Yes, this is expected and usually chips don't care.

> and
> driver will get incorrect ONFI parameter table data from 
> nand_read_data_op().
> 

Thanks,
Miquèl