Re: [PATCH] mtd: rawnand: denali: add more delays before latching incoming data

[Marek Vasut]

On 3/22/20 6:42 PM, Masahiro Yamada wrote:
> On Sat, Mar 21, 2020 at 2:15 AM Marek Vasut <marex@xxxxxxx> wrote:
>>
>> On 3/20/20 6:11 PM, Miquel Raynal wrote:
>>> Hi Marek,
>>>
>>> Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> wrote on Mon, 16 Mar
>>> 2020 19:43:07 +0900:
>>>
>>>> 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@xxxxxxx>
>>>> Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
>>>> ---
>>>
>>> Can you please give this patch a try and report the result?
>>
>> It's on my list, don't worry.
> 
> 
> Preferably, please test v2.

Yes, I see the V2.