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

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Date:   Mon, 23 Mar 2020 02:42:48 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Marek Vasut <marex@...x.de>
Cc:     Miquel Raynal <miquel.raynal@...tlin.com>,
        linux-mtd <linux-mtd@...ts.infradead.org>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mtd: rawnand: denali: add more delays before latching
 incoming data

On Sat, Mar 21, 2020 at 2:15 AM Marek Vasut <marex@...x.de> wrote:
>
> On 3/20/20 6:11 PM, Miquel Raynal wrote:
> > Hi Marek,
> >
> > Masahiro Yamada <yamada.masahiro@...ionext.com> 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@...x.de>
> >> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> >> ---
> >
> > Can you please give this patch a try and report the result?
>
> It's on my list, don't worry.


Preferably, please test v2.

Thanks.


-- 
Best Regards
Masahiro Yamada