Re: [PATCH v2 2/5] mtd: rawnand: mtk: Improve data sampling timing for read cycle

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Xiaolei,

Xiaolei Li <xiaolei.li@mediatek.com> wrote on Tue, 30 Apr 2019 18:02:47
+0800:

> Currently, we expand RE# low level time by choosing the max value
> between RE# pulse width and RE# access time, and sample data at the
> rising edge of RE#.
> 
> Then, if RE# access time is bigger than RE# pulse width, the real
> read cycle time may be more than NAND SPEC required. This makes
> read performance be worse than that expected.
> 
> This patch improves data sampling timing by calculating RE# low level
> time according to RE# pulse width. If RE# access time is bigger than
> RE# pulse width, then delay sampling data timing.
> 
> The result of contrast test base on MT2712 evaluat board is as follow.
> 
> nand: Micron MT29F16G08ADBCAH4
> nand: 2048 MiB, SLC, erase size: 256 KiB, page size: 4096, OOB size: 224
> NFI 2x clock rate: 124800000 HZ.
> 
> Read speed without this patch:
> mtd_speedtest: page read speed is 14012 KiB/s
> mtd_speedtest: 2 page read speed is 14860 KiB/s
> 
> Read speed with this patch:
> mtd_speedtest: page read speed is 18724 KiB/s
> mtd_speedtest: 2 page read speed is 18713 KiB/s
> 
> Signed-off-by: Xiaolei Li <xiaolei.li@mediatek.com>
> ---
>  drivers/mtd/nand/raw/mtk_nand.c | 46 ++++++++++++++++++++++++++-------
>  1 file changed, 36 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/mtd/nand/raw/mtk_nand.c b/drivers/mtd/nand/raw/mtk_nand.c
> index 4fbb0c6ecae3..e90c38c6f835 100644
> --- a/drivers/mtd/nand/raw/mtk_nand.c
> +++ b/drivers/mtd/nand/raw/mtk_nand.c
> @@ -87,6 +87,10 @@
>  #define NFI_FDMM(x)		(0xA4 + (x) * sizeof(u32) * 2)
>  #define NFI_FDM_MAX_SIZE	(8)
>  #define NFI_FDM_MIN_SIZE	(1)
> +#define NFI_DEBUG_CON1		(0x220)
> +#define		STROBE_MASK		GENMASK(4, 3)
> +#define		STROBE_SHIFT		(3)
> +#define		MAX_STROBE_DLY		(3)
>  #define NFI_MASTER_STA		(0x224)
>  #define		MASTER_STA_MASK		(0x0FFF)
>  #define NFI_EMPTY_THRESH	(0x23C)
> @@ -509,7 +513,7 @@ 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 = 0, trlt = 0;
> -	u32 thold;
> +	u32 temp, tsel = 0;
>  
>  	timings = nand_get_sdr_timings(conf);
>  	if (IS_ERR(timings))
> @@ -546,30 +550,52 @@ static int mtk_nfc_setup_data_interface(struct nand_chip *chip, int csline,
>  	twh &= 0xf;
>  
>  	/* Calculate real WE#/RE# hold time in nanosecond */
> -	thold = (twh + 1) * 1000000 / rate;
> +	temp = (twh + 1) * 1000000 / rate;
>  	/* nanosecond to picosecond */
> -	thold *= 1000;
> +	temp *= 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;
> +	if (temp < timings->tWC_min)
> +		twst = timings->tWC_min - temp;
>  	twst = max(timings->tWP_min, twst) / 1000;
>  	twst = DIV_ROUND_UP(twst * rate, 1000000) - 1;
>  	twst &= 0xf;
>  
>  	/**
> -	 * RE# low level time should be expaned to meet RE# pulse time,
> -	 * RE# access time and RE# cycle time at the same time.
> +	 * RE# low level time should be expaned to meet RE# pulse 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;
> +	if (temp < timings->tRC_min)
> +		trlt = timings->tRC_min - temp;
> +	trlt = max(trlt, timings->tRP_min) / 1000;
>  	trlt = DIV_ROUND_UP(trlt * rate, 1000000) - 1;
>  	trlt &= 0xf;
>  
> +	/**

        /*

> +	 * Calculate strobe select timing.
> +	 * If RE# access time is bigger than RE# pulse time,
> +	 * delay sampling data timing.
> +	 */
> +	temp = (trlt + 1) * 1000000 / rate;

You could precise what unit conversion you do here.

> +	/* nanosecond to picosecond */
> +	temp *= 1000;
> +	if (temp < timings->tREA_max) {
> +		tsel = timings->tREA_max / 1000;
> +		tsel = DIV_ROUND_UP(tsel * rate, 1000000);
> +		tsel -= (trlt + 1);
> +		if (tsel > MAX_STROBE_DLY) {
> +			trlt += tsel - MAX_STROBE_DLY;
> +			tsel = MAX_STROBE_DLY;
> +		}
> +	}
> +	temp = nfi_readl(nfc, NFI_DEBUG_CON1);
> +	temp &= ~STROBE_MASK;
> +	temp |= tsel << STROBE_SHIFT;
> +	nfi_writel(nfc, temp, NFI_DEBUG_CON1);
> +
>  	/*
>  	 * ACCON: access timing control register
>  	 * -------------------------------------

With this:

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


Thanks,
Miquèl

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