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Subject: Re: [RFC PATCH v2 2/2] mtd: rawnand: meson: add support for Amlogic
 NAND flash controller
From:   Liang Yang <liang.yang@amlogic.com>
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>
 <fdea2d54-7a68-64ec-8bb4-4a94677a3293@amlogic.com>
 <20180828152645.457dab5c@bbrezillon>
 <9abf0461-159b-db45-9ded-3d6cb2cc64db@amlogic.com>
Message-ID: <5061c929-8db0-3f4c-ec34-303fc351dfdd@amlogic.com>
Date:   Wed, 29 Aug 2018 18:29:05 +0800
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On 8/29/2018 6:08 PM, Liang Yang wrote:
> 
> On 8/28/2018 9:26 PM, Boris Brezillon wrote:
>> On Tue, 28 Aug 2018 21:21:48 +0800
>> Liang Yang <liang.yang@amlogic.com> wrote:
>>
>>> 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?
>>
>> Hm, no. If you initialize the time you compare to (using time_before()
>> or time_after()) correctly it should not happen. Anyway, I keep thinking
>> this is not how it should be done. Did you try NFC_CMD_RB? Did you ask
>> HW designers what it was created for?
>>
> I am using NFC_CMD_RB and checking with irq. it is ok now.
there are two usages for NFC_CMD_RB. One reads the data status 
continuously by hardware after sending 0x70 command; the other checks 
the r/b IO status continuously.both can send irq when r/b is ready.

>> .
>>