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SubjectRe: [PATCH 1/2] mtd: m25p80: Rework probing/JEDEC code
On Wed, Aug 19, 2009 at 5:46 AM, Anton Vorontsov
<avorontsov@ru.mvista.com> wrote:
>
> Previosly the driver always tried JEDEC probing, assuming that non-JEDEC
> chips will return '0'. But truly non-JEDEC chips (like CAT25) won't do
> that, their behaviour on RDID command is undefined, so the driver should
> not call jedec_probe() for these chips.
>
> Also, be less strict on error conditions, don't fail to probe if JEDEC
> found a chip that is different from what platform code told, instead
> just print some warnings and use an information obtained via JEDEC. In
This patch caused a problem:
even though the external flash doesn't exist, it will still pass the
probe() and be registerred into kernel and given the partition table.
You may refer to this bug report:
http://blackfin.uclinux.org/gf/project/uclinux-dist/tracker/?action=TrackerItemEdit&tracker_item_id=5975&start=0

> that case we should not trust partitions any longer, but they might be
> still useful (i.e. they could protect some parts of the chip).
>
> Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
> ---
>  drivers/mtd/devices/m25p80.c |   69 ++++++++++++++++++++++++-----------------
>  1 files changed, 40 insertions(+), 29 deletions(-)
>
> diff --git a/drivers/mtd/devices/m25p80.c b/drivers/mtd/devices/m25p80.c
> index 0d74b38..b75e319 100644
> --- a/drivers/mtd/devices/m25p80.c
> +++ b/drivers/mtd/devices/m25p80.c
> @@ -581,6 +581,14 @@ static const struct spi_device_id *__devinit jedec_probe(struct spi_device *spi)
>        jedec = jedec << 8;
>        jedec |= id[2];
>
> +       /*
> +        * Some chips (like Numonyx M25P80) have JEDEC and non-JEDEC variants,
> +        * which depend on technology process. Officially RDID command doesn't
> +        * exist for non-JEDEC chips, but for compatibility they return ID 0.
> +        */
> +       if (jedec == 0)
> +               return NULL;
> +
>        ext_jedec = id[3] << 8 | id[4];
>
>        for (tmp = 0; tmp < ARRAY_SIZE(m25p_ids) - 1; tmp++) {
> @@ -602,7 +610,7 @@ static const struct spi_device_id *__devinit jedec_probe(struct spi_device *spi)
>  */
>  static int __devinit m25p_probe(struct spi_device *spi)
>  {
> -       const struct spi_device_id      *id;
> +       const struct spi_device_id      *id = spi_get_device_id(spi);
>        struct flash_platform_data      *data;
>        struct m25p                     *flash;
>        struct flash_info               *info;
> @@ -615,41 +623,44 @@ static int __devinit m25p_probe(struct spi_device *spi)
>         */
>        data = spi->dev.platform_data;
>        if (data && data->type) {
> +               const struct spi_device_id *plat_id;
> +
>                for (i = 0; i < ARRAY_SIZE(m25p_ids) - 1; i++) {
> -                       id = &m25p_ids[i];
> -                       info = (void *)m25p_ids[i].driver_data;
> -                       if (strcmp(data->type, id->name))
> +                       plat_id = &m25p_ids[i];
> +                       if (strcmp(data->type, plat_id->name))
>                                continue;
>                        break;
>                }
>
> -               /* unrecognized chip? */
> -               if (i == ARRAY_SIZE(m25p_ids) - 1) {
> -                       DEBUG(MTD_DEBUG_LEVEL0, "%s: unrecognized id %s\n",
> -                                       dev_name(&spi->dev), data->type);
> -                       info = NULL;
> -
> -               /* recognized; is that chip really what's there? */
> -               } else if (info->jedec_id) {
> -                       id = jedec_probe(spi);
> -
> -                       if (id != &m25p_ids[i]) {
> -                               dev_warn(&spi->dev, "found %s, expected %s\n",
> -                                               id ? id->name : "UNKNOWN",
> -                                               m25p_ids[i].name);
> -                               info = NULL;
> -                       }
> -               }
> -       } else {
> -               id = jedec_probe(spi);
> -               if (!id)
> -                       id = spi_get_device_id(spi);
> -
> -               info = (void *)id->driver_data;
> +               if (plat_id)
> +                       id = plat_id;
> +               else
> +                       dev_warn(&spi->dev, "unrecognized id %s\n", data->type);
>        }
>
> -       if (!info)
> -               return -ENODEV;
> +       info = (void *)id->driver_data;
> +
> +       if (info->jedec_id) {
> +               const struct spi_device_id *jid;
> +
> +               jid = jedec_probe(spi);
> +               if (!jid) {
> +                       dev_info(&spi->dev, "non-JEDEC variant of %s\n",
> +                                id->name);
> +               } else if (jid != id) {
> +                       /*
> +                        * JEDEC knows better, so overwrite platform ID. We
> +                        * can't trust partitions any longer, but we'll let
> +                        * mtd apply them anyway, since some partitions may be
> +                        * marked read-only, and we don't want to lose that
> +                        * information, even if it's not 100% accurate.
> +                        */
> +                       dev_warn(&spi->dev, "found %s, expected %s\n",
> +                                jid->name, id->name);
> +                       id = jid;
> +                       info = (void *)jid->driver_data;
> +               }
> +       }
>
>        flash = kzalloc(sizeof *flash, GFP_KERNEL);
>        if (!flash)
> --
> 1.6.3.3
>
> --
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