linux-kernel - Re: [PATCH 1/2] mtd: spi-nor: sfdp: save a copy of the SFDP data

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Message-ID: <e28e7cd3-9728-3428-1bae-9cda258174bc@microchip.com>
Date:   Mon, 5 Apr 2021 13:11:19 +0000
From:   <Tudor.Ambarus@...rochip.com>
To:     <michael@...le.cc>, <linux-kernel@...r.kernel.org>,
        <linux-mtd@...ts.infradead.org>
CC:     <p.yadav@...com>, <miquel.raynal@...tlin.com>, <richard@....at>,
        <vigneshr@...com>
Subject: Re: [PATCH 1/2] mtd: spi-nor: sfdp: save a copy of the SFDP data

Hi,

On 3/18/21 11:24 AM, Michael Walle wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> Due to possible mode switching to 8D-8D-8D, it might not be possible to
> read the SFDP after the initial probe. To be able to dump the SFDP via
> sysfs afterwards, make a complete copy of it.
> 
> Signed-off-by: Michael Walle <michael@...le.cc>
> ---
>  drivers/mtd/spi-nor/core.h  | 10 ++++++++
>  drivers/mtd/spi-nor/sfdp.c  | 49 +++++++++++++++++++++++++++++++++++++
>  include/linux/mtd/spi-nor.h |  3 +++
>  3 files changed, 62 insertions(+)
> 
> diff --git a/drivers/mtd/spi-nor/core.h b/drivers/mtd/spi-nor/core.h
> index 4a3f7f150b5d..668f22011b1d 100644
> --- a/drivers/mtd/spi-nor/core.h
> +++ b/drivers/mtd/spi-nor/core.h
> @@ -407,6 +407,16 @@ struct spi_nor_manufacturer {
>         const struct spi_nor_fixups *fixups;
>  };
> 
> +/**
> + * struct sfdp - SFDP data
> + * @num_dwords: number of entries in the dwords array
> + * @dwords: array of double words of the SFDP data
> + */
> +struct sfdp {
> +       size_t  num_dwords;
> +       u32     *dwords;
> +};
> +
>  /* Manufacturer drivers. */
>  extern const struct spi_nor_manufacturer spi_nor_atmel;
>  extern const struct spi_nor_manufacturer spi_nor_catalyst;
> diff --git a/drivers/mtd/spi-nor/sfdp.c b/drivers/mtd/spi-nor/sfdp.c
> index 25142ec4737b..2b6c96e02532 100644
> --- a/drivers/mtd/spi-nor/sfdp.c
> +++ b/drivers/mtd/spi-nor/sfdp.c
> @@ -16,6 +16,7 @@
>         (((p)->parameter_table_pointer[2] << 16) | \
>          ((p)->parameter_table_pointer[1] <<  8) | \
>          ((p)->parameter_table_pointer[0] <<  0))
> +#define SFDP_PARAM_HEADER_PARAM_LEN(p) ((p)->length * 4)
> 
>  #define SFDP_BFPT_ID           0xff00  /* Basic Flash Parameter Table */
>  #define SFDP_SECTOR_MAP_ID     0xff81  /* Sector Map Table */
> @@ -1263,6 +1264,8 @@ int spi_nor_parse_sfdp(struct spi_nor *nor,
>         struct sfdp_parameter_header *param_headers = NULL;
>         struct sfdp_header header;
>         struct device *dev = nor->dev;
> +       struct sfdp *sfdp;
> +       size_t sfdp_size;
>         size_t psize;
>         int i, err;
> 
> @@ -1285,6 +1288,9 @@ int spi_nor_parse_sfdp(struct spi_nor *nor,
>             bfpt_header->major != SFDP_JESD216_MAJOR)
>                 return -EINVAL;
> 
> +       sfdp_size = SFDP_PARAM_HEADER_PTP(bfpt_header) +
> +                   SFDP_PARAM_HEADER_PARAM_LEN(bfpt_header);
> +
>         /*
>          * Allocate memory then read all parameter headers with a single
>          * Read SFDP command. These parameter headers will actually be parsed
> @@ -1311,6 +1317,49 @@ int spi_nor_parse_sfdp(struct spi_nor *nor,
>                 }
>         }
> 
> +       /*
> +        * Cache the complete SFDP data. It is not (easily) possible to fetch
> +        * SFDP after probe time and we need it for the sysfs access.
> +        */
> +       for (i = 0; i < header.nph; i++) {
> +               param_header = &param_headers[i];
> +               sfdp_size = max_t(size_t, sfdp_size,
> +                                 SFDP_PARAM_HEADER_PTP(param_header) +
> +                                 SFDP_PARAM_HEADER_PARAM_LEN(param_header));
> +       }

Michael, I like the idea of saving the SFDP data, but I think this can be
improved a little. For example, it is not mandatory for the tables to be
continuous in memory, there can be some gaps between BFPT and SMPT for example,
thus we can improve the memory allocation logic. Also, we can make the saved sfdp
data table-agnostic so that we don't duplicate the reads in parse_bfpt/smpt/4bait.
Are you willing to respin?

Cheers,
ta