linux-kernel - Re: [PATCH v2] mtd: rawnand: denali: add more delays before latching incoming data

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Date:   Wed, 22 Apr 2020 17:37:47 +0200
From:   Marek Vasut <marex@...x.de>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        linux-mtd@...ts.infradead.org, Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mtd: rawnand: denali: add more delays before latching
 incoming data

On 4/22/20 5:36 PM, Miquel Raynal wrote:
> Hi Marek,
> 
> Marek Vasut <marex@...x.de> wrote on Wed, 22 Apr 2020 17:29:53 +0200:
> 
>> On 3/17/20 8:18 AM, Masahiro Yamada wrote:
>>> The Denali IP have several registers to specify how many clock cycles
>>> should be waited between falling/rising signals. You can improve the
>>> NAND access performance by programming these registers with optimized
>>> values.
>>>
>>> Because struct nand_sdr_timings represents the device requirement
>>> in pico seconds, denali_setup_data_interface() computes the register
>>> values by dividing the device timings with the clock period.
>>>
>>> Marek Vasut reported this driver in the latest kernel does not work
>>> on his SOCFPGA board. (The on-board NAND chip is mode 5)
>>>
>>> The suspicious parameter is acc_clks, so this commit relaxes it.
>>>
>>> The Denali NAND Flash Memory Controller User's Guide describes this
>>> register as follows:
>>>
>>>   acc_clks
>>>     signifies the number of bus interface clk_x clock cycles,
>>>     controller should wait from read enable going low to sending
>>>     out a strobe of clk_x for capturing of incoming data.
>>>
>>> Currently, acc_clks is calculated only based on tREA, the delay on the
>>> chip side. This does not include additional delays that come from the
>>> data path on the PCB and in the SoC, load capacity of the pins, etc.
>>>
>>> This relatively becomes a big factor on faster timing modes like mode 5.
>>>
>>> Before supporting the ->setup_data_interface() hook (e.g. Linux 4.12),
>>> the Denali driver hacks acc_clks in a couple of ways [1] [2] to support
>>> the timing mode 5.
>>>
>>> We would not go back to the hard-coded acc_clks, but we need to include
>>> this factor into the delay somehow. Let's say the amount of the additional
>>> delay is 10000 pico sec.
>>>
>>> In the new calculation, acc_clks is determined by timings->tREA_max +
>>> data_setup_on_host.
>>>
>>> Also, prolong the RE# low period to make sure the data hold is met.
>>>
>>> Finally, re-center the data latch timing for extra safety.
>>>
>>> [1] https://github.com/torvalds/linux/blob/v4.12/drivers/mtd/nand/denali.c#L276
>>> [2] https://github.com/torvalds/linux/blob/v4.12/drivers/mtd/nand/denali.c#L282
>>>
>>> Reported-by: Marek Vasut <marex@...x.de>
>>> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>  
>>
>> I tested it on the AV SoCFPGA, this seems to work, so feel free to apply.
> 
> 
> Great! Thanks a lot for testing, would you mind sending your Tested-by?

Lightly
Tested-by: Marek Vasut <marex@...x.de>