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Date:   Fri, 24 Aug 2018 14:48:10 +0200
From:   Boris Brezillon <boris.brezillon@bootlin.com>
To:     Liang Yang <liang.yang@amlogic.com>
Cc:     Yixun Lan <yixun.lan@amlogic.com>, <linux-mtd@lists.infradead.org>,
        Rob Herring <robh@kernel.org>,
        Neil Armstrong <narmstrong@baylibre.com>,
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        Richard Weinberger <richard@nod.at>,
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        Marek Vasut <marek.vasut@gmail.com>,
        Jian Hu <jian.hu@amlogic.com>,
        Kevin Hilman <khilman@baylibre.com>,
        Carlo Caione <carlo@caione.org>,
        <linux-amlogic@lists.infradead.org>,
        Brian Norris <computersforpeace@gmail.com>,
        David Woodhouse <dwmw2@infradead.org>,
        <linux-arm-kernel@lists.infradead.org>,
        Jerome Brunet <jbrunet@baylibre.com>
Subject: Re: [RFC PATCH v2 2/2] mtd: rawnand: meson: add support for Amlogic
 NAND flash controller
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On Wed, 22 Aug 2018 22:08:42 +0800
Liang Yang <liang.yang@amlogic.com> wrote:

> > You have to wait tWB, that's for sure.
> >   
> we have a maximum 32 commands fifo. when command is written into 
> NFC_REG_CMD, it doesn't mean that command is executing right now, maybe 
> it is buffering on the queue.Assume one ERASE operation, when 2nd 
> command(0xd0) is written into NFC_REG_CMD and then come into 
> NAND_OP_WAITRDY_INSTR, if I read the RB status by register, it may be 
> wrong because 0xd0 may not being executed. it is unusual unless 
> buffering two many command.

You should flush the queue and wait for it to empty at the end of
->exec_op().

> so it seems that i still need to use nand_soft_waitrdy or wait cmd is 
> executed somewhere.

Don't you have a WAIT_FOR_RB instruction? What is NFC_CMD_RB for? Also,
NFC_CMD_IDLE seems to allow you to add an arbitrary delay, and that's
probably what you should use for tWB.