Re: [PATCH] mtd: rawnand: arasan: Fix clock rate in NV-DDR

From: Miquel Raynal
Date: Tue Nov 30 2021 - 02:20:23 EST


Hi Olga,

okitain@xxxxxxxxx wrote on Mon, 29 Nov 2021 21:06:05 +0300:

> Hi Miquel,
>
> On 29.11.2021 11:55, Miquel Raynal wrote:
> > Hi Olga,
> >
> > Please add all the MTD maintainers in copy, as requested by
> > get_maintainers.pl.
> >
> > okitain@xxxxxxxxx wrote on Sat, 27 Nov 2021 21:07:58
> > +0300:
> >
> >> According to the Arasan NAND controller spec,
> >> the flash clock rate for SDR must be <= 100 MHz,
> >> while for NV-DDR it must be the same as the rate
> >> of the CLK line for the mode.
> >
> > I completely missed that, where did you get the information?
>
> The "Data Interface Transitions" chapter of the spec contains timings for flash clock setup in NV-DDR
> and NV-DDR2 modes. The "time period" of those clocks is equal to tCK in NV-DDR and tRC in NV-DDR2.
>
> The same chapter should have information about necessary steps to switch from NV-DDR to SDR,
> which includes setting the flash clock to 100 MHz.
>
>
> Just to make sure i'm not shooting myself in the foot: am I changing the right clock?
> The documentation points out that we have to change flash_clk, which i thought was
> nfc->controller_clk and set up by anand->clk, but it seems like it might actually be nfc->bus_clk.

I believe I made a serious mistake, re-reading the code it feels like
I'm changing the system's clock (which basically changes nothing in our
case) instead of changing the NAND bus clock.

> In that case, does setting nfc->controller_clk to 100 MHz by default make sense?
> There isn't a hard limit on what the system clock might be (beyond a specific SoC),
> but there are timing requirements for the flash clock, and so setting a specific
> system clock frequency seems unnecessary for most devices.
>

Please create a two-patch series:
1- Setting the right clock in the current code base (inverting bus_clk
and controller_clk where relevant, setting one to 100MHz and letting
the other as it is)
2- Changing the default NV-DDR rate based on tCK (below patch).

Do you have the necessary hardware for testing?

> >> The driver previously always set 100 MHz for NV-DDR, which
> >> would result in incorrect behavior for NV-DDR modes 0-4.
> >>
> >> The appropriate clock rate can be calculated
> >> from the NV-DDR timing parameters as 1/tCK, or for rates
> >> measured in picoseconds, 10^12 / nand_nvddr_timings->tCK_min.
> >>
> >
> > You need a couple of Fixes + Cc: stable tags here, otherwise the
> > patch looks good to me.
> >
>
> Will include in the next iteration of the patch, thank you.
>
> >> Signed-off-by: Olga Kitaina <okitain@xxxxxxxxx>
> >> ---
> >> drivers/mtd/nand/raw/arasan-nand-controller.c | 8 +++++++-
> >> 1 file changed, 7 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/mtd/nand/raw/arasan-nand-controller.c b/drivers/mtd/nand/raw/arasan-nand-controller.c
> >> index 53bd10738418..ed4ee9942441 100644
> >> --- a/drivers/mtd/nand/raw/arasan-nand-controller.c
> >> +++ b/drivers/mtd/nand/raw/arasan-nand-controller.c
> >> @@ -18,6 +18,7 @@
> >> #include <linux/gpio/consumer.h>
> >> #include <linux/interrupt.h>
> >> #include <linux/iopoll.h>
> >> +#include <linux/math64.h>
> >> #include <linux/module.h>
> >> #include <linux/mtd/mtd.h>
> >> #include <linux/mtd/partitions.h>
> >> @@ -1043,7 +1044,12 @@ static int anfc_setup_interface(struct nand_chip *chip, int target,
> >> DQS_BUFF_SEL_OUT(dqs_mode);
> >> }
> >>
> >> - anand->clk = ANFC_XLNX_SDR_DFLT_CORE_CLK;
> >> + if (nand_interface_is_sdr)
> >> + anand->clk = ANFC_XLNX_SDR_DFLT_CORE_CLK;
> >> + else
> >> + /* ONFI timings are defined in picoseconds */
> >> + anand->clk = div_u64((u64)NSEC_PER_SEC * 1000,
> >> + conf->timings.nvddr.tCK_min);
> >>
> >> /*
> >> * Due to a hardware bug in the ZynqMP SoC, SDR timing modes 0-1 work
> >>
> >> base-commit: f53d4c109a666bf1a4883b45d546fba079258717
> >
> >
> > Thanks,
> > Miquèl
> >


Thanks,
Miquèl