Re: [PATCH v2 07/14] mtd: spinand: Allow enabling Octal DTR mode in the core

[Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>]

On Tue, 12 Oct 2021 02:16:12 +0530
Apurva Nandan <a-nandan@xxxxxx> wrote:

> Enable Octal DTR SPI mode, i.e. 8D-8D-8D mode, if the SPI NAND flash
> device supports it. Mixed OSPI (1S-1S-8S & 1S-8S-8S), mixed DTR modes
> (1S-1D-8D), etc. aren't supported yet.
> 
> The method to switch to Octal DTR SPI mode may vary across
> manufacturers. For example, for Winbond, it is enabled by writing
> values to the volatile configuration register. So, let the
> manufacturer's code have their own implementation for switching to
> Octal DTR SPI mode.
> 
> Check for the SPI NAND device's support for Octal DTR mode using
> spinand flags, and if the op_templates allows 8D-8D-8D, call
> octal_dtr_enable() manufacturer op. If the SPI controller doesn't
> supports these modes, the selected op_templates will prevent switching
> to the Octal DTR mode. And finally update the spinand reg_proto
> on success.
> 
> Signed-off-by: Apurva Nandan <a-nandan@xxxxxx>
> ---
>  drivers/mtd/nand/spi/core.c | 46 +++++++++++++++++++++++++++++++++++++
>  include/linux/mtd/spinand.h |  3 +++
>  2 files changed, 49 insertions(+)
> 
> diff --git a/drivers/mtd/nand/spi/core.c b/drivers/mtd/nand/spi/core.c
> index 8e6cf7941a0f..1210946f8447 100644
> --- a/drivers/mtd/nand/spi/core.c
> +++ b/drivers/mtd/nand/spi/core.c
> @@ -257,6 +257,48 @@ static int spinand_init_quad_enable(struct spinand_device *spinand)
>  			       enable ? CFG_QUAD_ENABLE : 0);
>  }
>  
> +static bool spinand_op_is_octal_dtr(const struct spi_mem_op *op)
> +{
> +	return  op->cmd.buswidth == 8 && op->cmd.dtr &&
> +		op->addr.buswidth == 8 && op->addr.dtr &&
> +		op->data.buswidth == 8 && op->data.dtr;
> +}
> +
> +static int spinand_init_octal_dtr_enable(struct spinand_device *spinand)

I see no spinand_octal_dtr_disable(), and I feel like we'll want to get
back to single-STR mode just before rebooting/kexec-ing, or if/when
we need to execute other maintenance operations. Actually, I think we
should have something more generic to enter a new mode (see below
for a detailed explanation).

> +{
> +	struct device *dev = &spinand->spimem->spi->dev;
> +	int ret;
> +
> +	if (!(spinand->flags & SPINAND_HAS_OCTAL_DTR_BIT))
> +		return 0;
> +
> +	if (!(spinand_op_is_octal_dtr(spinand->op_templates.read_cache) &&
> +	      spinand_op_is_octal_dtr(spinand->op_templates.write_cache) &&
> +	      spinand_op_is_octal_dtr(spinand->op_templates.update_cache)))
> +		return 0;

Ok, so you check the controller-side octal-DTR capability when selecting
the read/write/update_cache variants, but what if other commands (reg
access, erase, ...) can't be issued in this mode? I really think all
the commands you might use should be tested at probe time, not just
these 3 operations.

> +
> +	if (!spinand->manufacturer->ops->octal_dtr_enable) {
> +		dev_dbg(dev,
> +			"Missing ->octal_dtr_enable(), unable to switch mode\n");
> +		return -EINVAL;
> +	}
> +
> +	ret = spinand->manufacturer->ops->octal_dtr_enable(spinand);
> +	if (ret) {
> +		dev_err(dev,
> +			"Failed to enable Octal DTR SPI mode (err = %d)\n",
> +			ret);
> +		return ret;
> +	}
> +
> +	spinand->reg_proto = SPINAND_OCTAL_DTR;
> +
> +	dev_dbg(dev,
> +		"%s SPI NAND switched to Octal DTR SPI (8D-8D-8D) mode\n",
> +		spinand->manufacturer->name);
> +	return 0;
> +}
> +
>  static int spinand_ecc_enable(struct spinand_device *spinand,
>  			      bool enable)
>  {
> @@ -1192,6 +1234,10 @@ static int spinand_init_flash(struct spinand_device *spinand)
>  	if (ret)
>  		return ret;
>  
> +	ret = spinand_init_octal_dtr_enable(spinand);
> +	if (ret)
> +		return ret;
> +

Why not delaying the 'enter fastest available mode' at the end of this
initialization? I fear some flashes won't support some of the
maintenance commands in 8-8-8-DTR, so it's probably safer to enter it
once you've initialized everything else.

>  	ret = spinand_upd_cfg(spinand, CFG_OTP_ENABLE, 0);
>  	if (ret)
>  		return ret;
> diff --git a/include/linux/mtd/spinand.h b/include/linux/mtd/spinand.h
> index 35816b8cfe81..daa2ac5c3110 100644
> --- a/include/linux/mtd/spinand.h
> +++ b/include/linux/mtd/spinand.h
> @@ -271,6 +271,7 @@ struct spinand_devid {
>   * @init: initialize a SPI NAND device
>   * @adjust_op: modify the ops for any variation in their cmd, address, dummy or
>   *	       data phase by the manufacturer
> + * @octal_dtr_enable: switch the SPI NAND flash into Octal DTR SPI mode
>   * @cleanup: cleanup a SPI NAND device
>   *
>   * Each SPI NAND manufacturer driver should implement this interface so that
> @@ -280,6 +281,7 @@ struct spinand_manufacturer_ops {
>  	int (*init)(struct spinand_device *spinand);
>  	void (*adjust_op)(struct spi_mem_op *op,
>  			  const enum spinand_proto reg_proto);
> +	int (*octal_dtr_enable)(struct spinand_device *spinand);

I'd probably opt for a more generic name and pass the spinand_protocol
you want to enter in:

	int (*change_mode)(struct spinand_device *spinand,
			   enum spinand_protocol proto);

This way we can get back to 1-1-1-STR if we have to, and we can also
easily extend the logic to support 4-4-4-STR and 8-8-8-STR, which,
IIRC, are a thing (at least they exist on SPI NORs).

>  	void (*cleanup)(struct spinand_device *spinand);
>  };
>  
> @@ -348,6 +350,7 @@ struct spinand_ecc_info {
>  
>  #define SPINAND_HAS_QE_BIT		BIT(0)
>  #define SPINAND_HAS_CR_FEAT_BIT		BIT(1)
> +#define SPINAND_HAS_OCTAL_DTR_BIT	BIT(2)
>  
>  /**
>   * struct spinand_ondie_ecc_conf - private SPI-NAND on-die ECC engine structure