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

From: Marek Vasut
Date: Wed Apr 22 2020 - 11:30:00 EST


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@xxxxxxx>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>

I tested it on the AV SoCFPGA, this seems to work, so feel free to apply.