linux-kernel - Re: [PATCH v2 2/3] mtd: spi-nor: core: Allow flashes to specify MTD writesize

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Message-ID: <939dcad9-b556-ea3e-9eca-c008a86fd01b@microchip.com>
Date:   Sat, 28 Nov 2020 10:59:30 +0000
From:   <Tudor.Ambarus@...rochip.com>
To:     <p.yadav@...com>, <miquel.raynal@...tlin.com>, <richard@....at>,
        <vigneshr@...com>, <linux-mtd@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] mtd: spi-nor: core: Allow flashes to specify MTD
 writesize

On 11/18/20 8:24 PM, Pratyush Yadav wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> Some flashes like the Cypress S28 family use ECC. Under this ECC scheme,
> multi-pass writes to an ECC block is not allowed. In other words, once
> data is programmed to an ECC block, it can't be programmed again without
> erasing it first.
> 
> Upper layers like file systems need to be given this information so they
> do not cause error conditions on the flash by attempting multi-pass
> programming. This can be done by setting 'writesize' in 'struct
> mtd_info'.
> 
> Set the default to 1 but allow flashes to modify it in fixup hooks. If
> more flashes show up with this constraint in the future it might be
> worth it to add it to 'struct flash_info', but for now increasing its
> size is not worth it.
> 
> Signed-off-by: Pratyush Yadav <p.yadav@...com>
> ---
> 
> Notes:
>     New in v2.
> 
>  drivers/mtd/spi-nor/core.c | 4 +++-
>  drivers/mtd/spi-nor/core.h | 3 +++
>  2 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
> index 5bee7c8da4dc..80fbcb9c0828 100644
> --- a/drivers/mtd/spi-nor/core.c
> +++ b/drivers/mtd/spi-nor/core.c
> @@ -3054,6 +3054,8 @@ static int spi_nor_init_params(struct spi_nor *nor)
>         if (!nor->params)
>                 return -ENOMEM;
> 
> +       nor->params->writesize = 1;
> +

please do default inits in spi_nor_info_init_params(). A good place would be:

--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -2885,6 +2885,7 @@ static void spi_nor_info_init_params(struct spi_nor *nor)
        nor->flags |= SNOR_F_HAS_16BIT_SR;
 
        /* Set SPI NOR sizes. */
+       params->writesize = 1;
        params->size = (u64)info->sector_size * info->n_sectors;
        params->page_size = info->page_size;


>         spi_nor_info_init_params(nor);
> 
>         spi_nor_manufacturer_init_params(nor);
> @@ -3430,7 +3432,7 @@ int spi_nor_scan(struct spi_nor *nor, const char *name,
>                 mtd->name = dev_name(dev);
>         mtd->priv = nor;
>         mtd->type = MTD_NORFLASH;
> -       mtd->writesize = 1;
> +       mtd->writesize = nor->params->writesize;
>         mtd->flags = MTD_CAP_NORFLASH;
>         mtd->size = nor->params->size;
>         mtd->_erase = spi_nor_erase;
> diff --git a/drivers/mtd/spi-nor/core.h b/drivers/mtd/spi-nor/core.h
> index 0a775a7b5606..413ea311e632 100644
> --- a/drivers/mtd/spi-nor/core.h
> +++ b/drivers/mtd/spi-nor/core.h
> @@ -197,6 +197,8 @@ struct spi_nor_locking_ops {
>   * @rdsr_dummy:                dummy cycles needed for Read Status Register command.
>   * @rdsr_addr_nbytes:  dummy address bytes needed for Read Status Register
>   *                     command.
> + * @writesize          Minimal writable flash unit size. Defaults to 1. Set to
> + *                     ECC unit size for ECC-ed flashes.
>   * @hwcaps:            describes the read and page program hardware
>   *                     capabilities.
>   * @reads:             read capabilities ordered by priority: the higher index
> @@ -222,6 +224,7 @@ struct spi_nor_flash_parameter {
>         u32                             page_size;

I would put writesize before or after page_size, because they are related.
Also, it would probably avoid padding.

With these addressed, one can add:

Reviewed-by: Tudor Ambarus <tudor.ambarus@...rochip.com>

>         u8                              rdsr_dummy;
>         u8                              rdsr_addr_nbytes;
> +       u32                             writesize;
> 
>         struct spi_nor_hwcaps           hwcaps;
>         struct spi_nor_read_command     reads[SNOR_CMD_READ_MAX];
> --
> 2.28.0
>