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Subject: Re: [RFC PATCH v2 2/2] mtd: rawnand: meson: add support for Amlogic
 NAND flash controller
To:     Boris Brezillon <boris.brezillon@bootlin.com>
CC:     Yixun Lan <yixun.lan@amlogic.com>, <linux-mtd@lists.infradead.org>,
        Rob Herring <robh@kernel.org>,
        Neil Armstrong <narmstrong@baylibre.com>,
        Martin Blumenstingl <martin.blumenstingl@googlemail.com>,
        Richard Weinberger <richard@nod.at>,
        <linux-kernel@vger.kernel.org>,
        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>
References: <20180719094612.5833-1-yixun.lan@amlogic.com>
 <20180719094612.5833-3-yixun.lan@amlogic.com>
 <20180801235045.5b4d8211@bbrezillon>
 <42877a0d-9830-0626-3f64-e49a326eaa3c@amlogic.com>
 <20180817155608.5929b37a@bbrezillon>
 <96e538a5-1232-11f2-8b9e-5ddb09dcc2de@amlogic.com>
 <20180824144810.31c929a5@bbrezillon>
From:   Liang Yang <liang.yang@amlogic.com>
Message-ID: <fdea2d54-7a68-64ec-8bb4-4a94677a3293@amlogic.com>
Date:   Tue, 28 Aug 2018 21:21:48 +0800
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Hi Boris,

On 8/24/2018 8:48 PM, Boris Brezillon wrote:
> 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.
> 
> em, I can wait for RB by reading the status from register now. but when 
calling nand_soft_waitrdy, i really met a problem. One *jiffies* is 
about 4ms. When programming, it pass 1ms to 
instr->ctx.waitrdy.timeout_ms and nand_soft_waitrdy will be only one 
*jiffies* to reach timeout. And then calling nand_soft_waitrdy maybe at 
the tail of 4ms interval, it may only wait 100us and next jiffies 
arrive. Is it correct?
>