Re: [PATCH v2 1/5] mtd: rawnand: mtk: Correct low level time calculation of r/w cycle

[Miquel Raynal <miquel.raynal@xxxxxxxxxxx>]

Hi Xiaolei,

Xiaolei Li <xiaolei.li@xxxxxxxxxxxx> wrote on Tue, 30 Apr 2019 18:02:46
+0800:

> At present, the flow of calculating AC timing of read/write cycle in SDR
> mode is that:
> At first, calculate high hold time which is valid for both read and write
> cycle using the max value between tREH_min and tWH_min.
> Secondly, calculate WE# pulse width using tWP_min.
> Thridly, calculate RE# pulse width using the bigger one between tREA_max
> and tRP_min.
> 
> But NAND SPEC shows that Controller should also meet write/read cycle time.
> That is write cycle time should be more than tWC_min and read cycle should
> be more than tRC_min. Obviously, we do not achieve that now.
> 
> This patch corrects the low level time calculation to meet minimum
> read/write cycle time required. After getting the high hold time, WE# low
> level time will be promised to meet tWP_min and tWC_min requirement,
> and RE# low level time will be promised to meet tREA_max, tRP_min and
> tRC_min requirement.
> 
> Fixes: edfee3619c49 ("mtd: nand: mtk: add ->setup_data_interface() hook")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Xiaolei Li <xiaolei.li@xxxxxxxxxxxx>
> ---
>  drivers/mtd/nand/raw/mtk_nand.c | 24 +++++++++++++++++++++---
>  1 file changed, 21 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/mtd/nand/raw/mtk_nand.c b/drivers/mtd/nand/raw/mtk_nand.c
> index b6b4602f5132..4fbb0c6ecae3 100644
> --- a/drivers/mtd/nand/raw/mtk_nand.c
> +++ b/drivers/mtd/nand/raw/mtk_nand.c
> @@ -508,7 +508,8 @@ static int mtk_nfc_setup_data_interface(struct nand_chip *chip, int csline,
>  {
>  	struct mtk_nfc *nfc = nand_get_controller_data(chip);
>  	const struct nand_sdr_timings *timings;
> -	u32 rate, tpoecs, tprecs, tc2r, tw2r, twh, twst, trlt;
> +	u32 rate, tpoecs, tprecs, tc2r, tw2r, twh, twst = 0, trlt = 0;
> +	u32 thold;
>  
>  	timings = nand_get_sdr_timings(conf);
>  	if (IS_ERR(timings))
> @@ -544,11 +545,28 @@ static int mtk_nfc_setup_data_interface(struct nand_chip *chip, int csline,
>  	twh = DIV_ROUND_UP(twh * rate, 1000000) - 1;
>  	twh &= 0xf;
>  
> -	twst = timings->tWP_min / 1000;
> +	/* Calculate real WE#/RE# hold time in nanosecond */
> +	thold = (twh + 1) * 1000000 / rate;
> +	/* nanosecond to picosecond */
> +	thold *= 1000;
> +
> +	/**

        /*

> +	 * WE# low level time should be expaned to meet WE# pulse time
> +	 * and WE# cycle time at the same time.
> +	 */
> +	if (thold < timings->tWC_min)
> +		twst = timings->tWC_min - thold;
> +	twst = max(timings->tWP_min, twst) / 1000;
>  	twst = DIV_ROUND_UP(twst * rate, 1000000) - 1;
>  	twst &= 0xf;
>  
> -	trlt = max(timings->tREA_max, timings->tRP_min) / 1000;
> +	/**

Ditto

> +	 * RE# low level time should be expaned to meet RE# pulse time,
> +	 * RE# access time and RE# cycle time at the same time.
> +	 */
> +	if (thold < timings->tRC_min)
> +		trlt = timings->tRC_min - thold;
> +	trlt = max3(trlt, timings->tREA_max, timings->tRP_min) / 1000;
>  	trlt = DIV_ROUND_UP(trlt * rate, 1000000) - 1;
>  	trlt &= 0xf;
>  

With this fixed:

Reviewed-by: Miquel Raynal <miquel.raynal@xxxxxxxxxxx>


Thanks,
Miquèl

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