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To:     "Miquel Raynal" <miquel.raynal@bootlin.com>
Cc:     bbrezillon@kernel.org,
        "Boris Brezillon" <boris.brezillon@collabora.com>,
        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: <OFFCBB8981.B840C87C-ON48258423.00311FA8-48258423.0031EBDD@mxic.com.tw>
From:   masonccyang@mxic.com.tw
Date:   Mon, 24 Jun 2019 17:05:16 +0800
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Sender: linux-kernel-owner@vger.kernel.org
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Hi Miquel, 


> > > > > > > > > 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.

As I replied to Boris's email previously.
I think I have fixed the problem and the root cause is the our NFC's TX 
FIFO 
counter do a unnecessary reset in CS control function.
currently, doing CS# control in ->exec_op() is OK to me.

In addition, by Jones's comments about MFD, 
I will re-submit this raw NAND ctlr driver instead of MFD and raw-nand. 
----------------------------------------------------------------------->
MFD is for registering child devices of chips which offer 
genuine cross-subsystem functionality. 

It is not designed for mode selecting, or as a place to shove shared code 
just because a better location doesn't appear to exist. 
------------------------------------------------------------------------<

thanks & best regards,
Mason


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