[RFC PATCH v2 2/2] mtd: rawnand: meson: add support for Amlogic NAND flash controller

[liang.yang@amlogic.com (Liang Yang)]

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.
> .
>