linux-kernel - Re: [PATCH v2 1/3] UBI: Do not zero out EC and VID on ECC-ed NOR flashes

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Message-ID: <2f07715e-fe44-c5fd-6194-b74ba9f22545@microchip.com>
Date:   Sat, 28 Nov 2020 10:58:02 +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 1/3] UBI: Do not zero out EC and VID on ECC-ed NOR
 flashes

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
> 
> For NOR flashes EC and VID are zeroed out before an erase is issued to
> make sure UBI does not mistakenly treat the PEB as used and associate it
> with an LEB.
> 
> But on some flashes, like the Cypress Semper S28 SPI NOR flash family,
> multi-pass page programming is not allowed on the default ECC scheme.
> This means zeroing out these magic numbers will result in the flash
> throwing a page programming error.
> 
> Do not zero out EC and VID for such flashes. A writesize > 1 is an
> indication of an ECC-ed flash.
> 
> Signed-off-by: Pratyush Yadav <p.yadav@...com>
> ---
> 
> Notes:
>     Changes in v2:
> 
>     - Use mtd->writesize to check if multi-pass programming can be done
>       instead of using MTD_NO_MULTI_PASS_WRITE.
>     - Remove the assertion that a NOR flash most have writesize of 1.
> 
>  drivers/mtd/ubi/build.c | 4 +---
>  drivers/mtd/ubi/io.c    | 9 ++++++++-
>  2 files changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/mtd/ubi/build.c b/drivers/mtd/ubi/build.c
> index e85b04e9716b..25fd7816b1f4 100644
> --- a/drivers/mtd/ubi/build.c
> +++ b/drivers/mtd/ubi/build.c
> @@ -628,10 +628,8 @@ static int io_init(struct ubi_device *ubi, int max_beb_per1024)
>                 ubi->bad_peb_limit = get_bad_peb_limit(ubi, max_beb_per1024);
>         }
> 
> -       if (ubi->mtd->type == MTD_NORFLASH) {
> -               ubi_assert(ubi->mtd->writesize == 1);
> +       if (ubi->mtd->type == MTD_NORFLASH)
>                 ubi->nor_flash = 1;
> -       }
> 
>         ubi->min_io_size = ubi->mtd->writesize;
>         ubi->hdrs_min_io_size = ubi->mtd->writesize >> ubi->mtd->subpage_sft;
> diff --git a/drivers/mtd/ubi/io.c b/drivers/mtd/ubi/io.c
> index 14d890b00d2c..2f3312c31e51 100644
> --- a/drivers/mtd/ubi/io.c
> +++ b/drivers/mtd/ubi/io.c
> @@ -535,7 +535,14 @@ int ubi_io_sync_erase(struct ubi_device *ubi, int pnum, int torture)
>                 return -EROFS;
>         }
> 
> -       if (ubi->nor_flash) {
> +       /*
> +        * If the flash is ECC-ed then we have to erase the ECC block before we
> +        * can write to it. But the write is in preparation to an erase in the
> +        * first place. This means we cannot zero out EC and VID before the
> +        * erase and we just have to hope the flash starts erasing from the
> +        * start of the page.
> +        */
> +       if (ubi->nor_flash && ubi->mtd->writesize == 1) {

Are there any SPI NORs with ECC block size of 4 bytes? Should we call
nor_erase_prepare() in this case?

Anyway, there's none in SPI NOR as of now, so:

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

>                 err = nor_erase_prepare(ubi, pnum);
>                 if (err)
>                         return err;
> --
> 2.28.0
>