[PATCH v3] mtd: nand: denali: fix setup_data_interface to meet tCCS delay

[PATCH v3] mtd: nand: denali: fix setup_data_interface to meet tCCS delay

[Masahiro Yamada]

The WE_2_RE register specifies the number of clock cycles inserted
between the rising edge of #WE and the falling edge of #RE.

The current setup_data_interface implementation takes care of tWHR,
but tCCS is missing.  Wait for max(tCSS, tWHR) to meet the spec.

With setup_data_interface() properly programmed, the Denali NAND
controller can observe the timing, so NAND_WAIT_TCCS flag is unneeded.
Clarify this in the comment block.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
---

Changes in v3:
  - Remove comment abount NAND_WAIT_TWHR because 1/2 seems NACK

Changes in v2:
  - newly added

 drivers/mtd/nand/denali.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/mtd/nand/denali.c b/drivers/mtd/nand/denali.c
index 0b268ec..5124f8a 100644
--- a/drivers/mtd/nand/denali.c
+++ b/drivers/mtd/nand/denali.c
@@ -1004,8 +1004,14 @@ static int denali_setup_data_interface(struct mtd_info *mtd, int chipnr,
 	tmp |= FIELD_PREP(RE_2_RE__VALUE, re_2_re);
 	iowrite32(tmp, denali->reg + RE_2_RE);
 
-	/* tWHR -> WE_2_RE */
-	we_2_re = DIV_ROUND_UP(timings->tWHR_min, t_clk);
+	/*
+	 * tCCS, tWHR -> WE_2_RE
+	 *
+	 * With WE_2_RE properly set, the Denali controller automatically takes
+	 * care of the delay; the driver need not set NAND_WAIT_TCCS.
+	 */
+	we_2_re = DIV_ROUND_UP(max(timings->tCCS_min, timings->tWHR_min),
+			       t_clk);
 	we_2_re = min_t(int, we_2_re, TWHR2_AND_WE_2_RE__WE_2_RE);
 
 	tmp = ioread32(denali->reg + TWHR2_AND_WE_2_RE);
-- 
2.7.4

Re: [PATCH v3] mtd: nand: denali: fix setup_data_interface to meet tCCS delay

[Boris Brezillon]

On Fri, 29 Sep 2017 23:12:57 +0900
Masahiro Yamada <yamada.masahiro@socionext.com> wrote:

> The WE_2_RE register specifies the number of clock cycles inserted
> between the rising edge of #WE and the falling edge of #RE.
> 
> The current setup_data_interface implementation takes care of tWHR,
> but tCCS is missing.  Wait for max(tCSS, tWHR) to meet the spec.
> 
> With setup_data_interface() properly programmed, the Denali NAND
> controller can observe the timing, so NAND_WAIT_TCCS flag is unneeded.
> Clarify this in the comment block.

Applied.

Thanks,

Boris

> 
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> ---
> 
> Changes in v3:
>   - Remove comment abount NAND_WAIT_TWHR because 1/2 seems NACK
> 
> Changes in v2:
>   - newly added
> 
>  drivers/mtd/nand/denali.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mtd/nand/denali.c b/drivers/mtd/nand/denali.c
> index 0b268ec..5124f8a 100644
> --- a/drivers/mtd/nand/denali.c
> +++ b/drivers/mtd/nand/denali.c
> @@ -1004,8 +1004,14 @@ static int denali_setup_data_interface(struct mtd_info *mtd, int chipnr,
>  	tmp |= FIELD_PREP(RE_2_RE__VALUE, re_2_re);
>  	iowrite32(tmp, denali->reg + RE_2_RE);
>  
> -	/* tWHR -> WE_2_RE */
> -	we_2_re = DIV_ROUND_UP(timings->tWHR_min, t_clk);
> +	/*
> +	 * tCCS, tWHR -> WE_2_RE
> +	 *
> +	 * With WE_2_RE properly set, the Denali controller automatically takes
> +	 * care of the delay; the driver need not set NAND_WAIT_TCCS.
> +	 */
> +	we_2_re = DIV_ROUND_UP(max(timings->tCCS_min, timings->tWHR_min),
> +			       t_clk);
>  	we_2_re = min_t(int, we_2_re, TWHR2_AND_WE_2_RE__WE_2_RE);
>  
>  	tmp = ioread32(denali->reg + TWHR2_AND_WE_2_RE);