[PATCH] mtd: nand: atmel: Relax tADL_min constraint

[Quentin Schulz]

Hi Boris,

On 23/08/2017 20:45, Boris Brezillon (by way of Boris Brezillon
<boris.brezillon at free-electrons.com>) wrote:
> Version 4 of the ONFI spec mandates that tADL be at least 400 nanoseconds,
> but, depending on the master clock rate, 400 ns may not fit in the tADL
> field of the SMC reg. We need to relax the check and accept the -ERANGE
> return code.
> 
> Note that previous versions of the ONFI spec had a lower tADL_min (100 or
> 200 ns). It's not clear why this timing constraint got increased but it
> seems most NANDs are fine with values lower than 400ns, so we should be
> safe.
> 
> Fixes: f9ce2eddf176 ("mtd: nand: atmel: Add ->setup_data_interface() hooks")
> Signed-off-by: Boris Brezillon <boris.brezillon at free-electrons.com>
Tested-by: Quentin Schulz <quentin.schulz at free-electrons.com>

Thanks,
Quentin

> ---
>  drivers/mtd/nand/atmel/nand-controller.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/nand/atmel/nand-controller.c b/drivers/mtd/nand/atmel/nand-controller.c
> index 2c8baa0c2c4e..ceec21bd30c4 100644
> --- a/drivers/mtd/nand/atmel/nand-controller.c
> +++ b/drivers/mtd/nand/atmel/nand-controller.c
> @@ -1364,7 +1364,18 @@ static int atmel_smc_nand_prepare_smcconf(struct atmel_nand *nand,
>  	ret = atmel_smc_cs_conf_set_timing(smcconf,
>  					   ATMEL_HSMC_TIMINGS_TADL_SHIFT,
>  					   ncycles);
> -	if (ret)
> +	/*
> +	 * Version 4 of the ONFI spec mandates that tADL be at least 400
> +	 * nanoseconds, but, depending on the master clock rate, 400 ns may not
> +	 * fit in the tADL field of the SMC reg. We need to relax the check and
> +	 * accept the -ERANGE return code.
> +	 *
> +	 * Note that previous versions of the ONFI spec had a lower tADL_min
> +	 * (100 or 200 ns). It's not clear why this timing constraint got
> +	 * increased but it seems most NANDs are fine with values lower than
> +	 * 400ns, so we should be safe.
> +	 */
> +	if (ret && ret != -ERANGE)
>  		return ret;
>  
>  	ncycles = DIV_ROUND_UP(conf->timings.sdr.tAR_min, mckperiodps);
> 

-- 
Quentin Schulz, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com