Re: [PATCH v2 6/6] mtd: rawnand: davinci: Implement setup_interface() operation

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

Hi Bastien,

On 06/11/2024 at 09:55:07 +01, Bastien Curutchet <bastien.curutchet@bootlin.com> wrote:

> The setup_interface() operation isn't implemented. It forces the driver
> to use the ONFI mode 0, though it could use more optimal modes.
>
> Implement the setup_interface() operation. It uses the
> aemif_set_cs_timings() function from the AEMIF driver to update the
> chip select timings. The calculation of the register's contents is
> directly extracted from §20.3.2.3 of the DaVinci TRM [1]
>
> These timings are previously set by the AEMIF driver itself from
> device-tree properties. Therefore, IMHO, failing to update them in the
> setup_interface() isn't critical, which is why 0 is returned even when
> timings aren't updated.

Did you experience failures? Because I'd be more conservative and error
out loudly when something is wrong. In general it is a safest approach
on the long term. Here maybe you have good reasons to do differently, in
this case I am all ears.

> MAX_TH_PS and MAX_TSU_PS are the worst case timings based on the
> Keystone2 and DaVinci datasheets.
>
> [1] : https://www.ti.com/lit/ug/spruh77c/spruh77c.pdf
>
> Signed-off-by: Bastien Curutchet <bastien.curutchet@bootlin.com>
> ---
>  drivers/mtd/nand/raw/davinci_nand.c | 78 +++++++++++++++++++++++++++++
>  1 file changed, 78 insertions(+)
>
> diff --git a/drivers/mtd/nand/raw/davinci_nand.c b/drivers/mtd/nand/raw/davinci_nand.c
> index 563045c7ce08..2d0c564c8d17 100644
> --- a/drivers/mtd/nand/raw/davinci_nand.c
> +++ b/drivers/mtd/nand/raw/davinci_nand.c
> @@ -14,6 +14,7 @@
>  #include <linux/err.h>
>  #include <linux/iopoll.h>
>  #include <linux/kernel.h>
> +#include <linux/memory/ti-aemif.h>
>  #include <linux/module.h>
>  #include <linux/mtd/rawnand.h>
>  #include <linux/mtd/partitions.h>
> @@ -44,6 +45,9 @@
>  #define	MASK_ALE		0x08
>  #define	MASK_CLE		0x10
>  
> +#define MAX_TSU_PS		3000	/* Input setup time in ps */
> +#define MAX_TH_PS		1600	/* Input hold time in ps */
> +
>  struct davinci_nand_pdata {
>  	uint32_t		mask_ale;
>  	uint32_t		mask_cle;
> @@ -120,6 +124,7 @@ struct davinci_nand_info {
>  	uint32_t		core_chipsel;
>  
>  	struct clk		*clk;
> +	struct aemif_device	*aemif;
>  };
>  
>  static DEFINE_SPINLOCK(davinci_nand_lock);
> @@ -767,9 +772,81 @@ static int davinci_nand_exec_op(struct nand_chip *chip,
>  	return 0;
>  }
>  
> +#define TO_CYCLES(ps, period_ns) (DIV_ROUND_UP((ps) / 1000, (period_ns)))
> +
> +static int davinci_nand_setup_interface(struct nand_chip *chip, int chipnr,
> +					const struct nand_interface_config *conf)
> +{
> +	struct davinci_nand_info *info = to_davinci_nand(nand_to_mtd(chip));
> +	const struct nand_sdr_timings *sdr;
> +	struct aemif_cs_timings timings;
> +	s32 cfg, min, cyc_ns;
> +
> +	cyc_ns = 1000000000 / clk_get_rate(info->clk);
> +
> +	sdr = nand_get_sdr_timings(conf);
> +	if (IS_ERR(sdr))
> +		return PTR_ERR(sdr);
> +
> +	cfg = TO_CYCLES(sdr->tCLR_min, cyc_ns) - 1;
> +	timings.rsetup = cfg > 0 ? cfg : 0;
> +
> +	cfg = max_t(s32, TO_CYCLES(sdr->tREA_max + MAX_TSU_PS, cyc_ns),
> +		    TO_CYCLES(sdr->tRP_min, cyc_ns)) - 1;
> +	timings.rstrobe = cfg > 0 ? cfg : 0;
> +
> +	min = TO_CYCLES(sdr->tCEA_max + MAX_TSU_PS, cyc_ns) - 2;
> +	while ((s32)(timings.rsetup + timings.rstrobe) < min)
> +		timings.rstrobe++;

I see a lot of while loops which just stop if you reach a min/max, I
believe a slightly more robust approach should be attempted, and
returning errors when these limits are crossed would be probably
beneficial on the long term?

> +
> +	cfg = TO_CYCLES((s32)(MAX_TH_PS - sdr->tCHZ_max), cyc_ns) - 1;
> +	timings.rhold = cfg > 0 ? cfg : 0;
> +
> +	min = TO_CYCLES(sdr->tRC_min, cyc_ns) - 3;
> +	while ((s32)(timings.rsetup + timings.rstrobe + timings.rhold) < min)
> +		timings.rhold++;
> +
> +	cfg = TO_CYCLES((s32)(sdr->tRHZ_max - (timings.rhold + 1) * cyc_ns * 1000), cyc_ns);
> +	cfg = max_t(s32, cfg, TO_CYCLES(sdr->tCHZ_max, cyc_ns)) - 1;
> +	timings.ta = cfg > 0 ? cfg : 0;
> +
> +	cfg = TO_CYCLES(sdr->tWP_min, cyc_ns) - 1;
> +	timings.wstrobe = cfg > 0 ? cfg : 0;
> +
> +	cfg = max_t(s32, TO_CYCLES(sdr->tCLS_min, cyc_ns), TO_CYCLES(sdr->tALS_min, cyc_ns));
> +	cfg = max_t(s32, cfg, TO_CYCLES(sdr->tCS_min, cyc_ns)) - 1;
> +	timings.wsetup = cfg > 0 ? cfg : 0;
> +
> +	min = TO_CYCLES(sdr->tDS_min, cyc_ns) - 2;
> +	while ((s32)(timings.wsetup + timings.wstrobe) < min)
> +		timings.wstrobe++;
> +
> +	cfg = max_t(s32, TO_CYCLES(sdr->tCLH_min, cyc_ns), TO_CYCLES(sdr->tALH_min, cyc_ns));
> +	cfg = max_t(s32, cfg, TO_CYCLES(sdr->tCH_min, cyc_ns));
> +	cfg = max_t(s32, cfg, TO_CYCLES(sdr->tDH_min, cyc_ns)) - 1;
> +	timings.whold = cfg > 0 ? cfg : 0;
> +
> +	min = TO_CYCLES(sdr->tWC_min, cyc_ns) - 2;
> +	while ((s32)(timings.wsetup + timings.wstrobe + timings.whold) < min)
> +		timings.whold++;
> +
> +	dev_dbg(&info->pdev->dev, "RSETUP %x RSTROBE %x RHOLD %x\n",
> +		timings.rsetup, timings.rstrobe, timings.rhold);
> +	dev_dbg(&info->pdev->dev, "TA %x\n", timings.ta);
> +	dev_dbg(&info->pdev->dev, "WSETUP %x WSTROBE %x WHOLD %x\n",
> +		timings.wsetup, timings.wstrobe, timings.whold);
> +

Here you probably want to exit in the NAND_DATA_IFACE_CHECK_ONLY case.

> +	if (aemif_set_cs_timings(info->aemif, info->core_chipsel, &timings) < 0)
> +		dev_info(&info->pdev->dev,
> +			 "Failed to dynamically update the CS timings, keep them unchanged");
> +
> +	return 0;
> +}
> +

Thanks,
Miquèl

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