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

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Date:   Tue, 30 Nov 2021 08:20:17 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Olga Kitaina <okitain@...il.com>
Cc:     linux-mtd@...ts.infradead.org, nagasure@...inx.com, richard@....at,
        vigneshr@...com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd: rawnand: arasan: Fix clock rate in NV-DDR

Hi Olga,

okitain@...il.com 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@...il.com 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@...il.com>
> >> ---
> >>  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