linux-kernel - Re: [PATCH v2 3/8] mtd: spi-nor: core: Use auto-detection only once

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Date:   Thu, 31 Mar 2022 00:20:05 +0530
From:   Pratyush Yadav <p.yadav@...com>
To:     Michael Walle <michael@...le.cc>
CC:     <Tudor.Ambarus@...rochip.com>, <miquel.raynal@...tlin.com>,
        <richard@....at>, <vigneshr@...com>,
        <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <Nicolas.Ferre@...rochip.com>
Subject: Re: [PATCH v2 3/8] mtd: spi-nor: core: Use auto-detection only once

On 21/03/22 11:38PM, Michael Walle wrote:
> Am 2022-03-21 18:42, schrieb Pratyush Yadav:
> > On 21/03/22 12:50PM, Tudor.Ambarus@...rochip.com wrote:
> > > On 3/21/22 14:14, Pratyush Yadav wrote:
> > > > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> > > >
> > > > On 28/02/22 01:17PM, Tudor Ambarus wrote:
> > > >> In case spi_nor_match_name() returned NULL, the auto detection was
> > > >> issued twice. There's no reason to try to detect the same chip twice,
> > > >> do the auto detection only once.
> > > >>
> > > >> Signed-off-by: Tudor Ambarus <tudor.ambarus@...rochip.com>
> > > >> ---
> > > >>  drivers/mtd/spi-nor/core.c | 10 ++++++----
> > > >>  1 file changed, 6 insertions(+), 4 deletions(-)
> > > >>
> > > >> diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
> > > >> index f87cb7d3daab..b1d6fa65417d 100644
> > > >> --- a/drivers/mtd/spi-nor/core.c
> > > >> +++ b/drivers/mtd/spi-nor/core.c
> > > >> @@ -2894,13 +2894,15 @@ static const struct flash_info *spi_nor_match_name(struct spi_nor *nor,
> > > >>  static const struct flash_info *spi_nor_get_flash_info(struct spi_nor *nor,
> > > >>                                                      const char *name)
> > > >>  {
> > > >> -     const struct flash_info *info = NULL;
> > > >> +     const struct flash_info *info = NULL, *detected_info = NULL;
> > > >>
> > > >>       if (name)
> > > >>               info = spi_nor_match_name(nor, name);
> > > >>       /* Try to auto-detect if chip name wasn't specified or not found */
> > > >> -     if (!info)
> > > >> -             info = spi_nor_read_id(nor);
> > > >> +     if (!info) {
> > > >> +             detected_info = spi_nor_read_id(nor);
> > > >> +             info = detected_info;
> > > >> +     }
> > > >>       if (IS_ERR_OR_NULL(info))
> > > >>               return ERR_PTR(-ENOENT);
> > > >>
> > > >> @@ -2908,7 +2910,7 @@ static const struct flash_info *spi_nor_get_flash_info(struct spi_nor *nor,
> > > >>        * If caller has specified name of flash model that can normally be
> > > >>        * detected using JEDEC, let's verify it.
> > > >>        */
> > > >> -     if (name && info->id_len) {
> > > >> +     if (name && !detected_info && info->id_len) {
> > > >>               const struct flash_info *jinfo;
> > > >>
> > > >>               jinfo = spi_nor_read_id(nor);
> > > >
> > > > I think the flow can be a little bit better. How about:
> > > >
> > > >         if (name)
> > > >                 info = spi_nor_match_name();
> > > >
> > > >         if (!info) {
> > > >                 info = spi_nor_read_id();
> > > >                 if (IS_ERR_OR_NULL(info))
> > > >                         return ERR_PTR(-ENOENT);
> > > >
> > > >                 return info;
> > > >         }
> 
> +1 for the flow. But is it correct that we just ignore any former
> error and just replace it with ENOENT? Should we return NULL here
> and let the caller handle the translation from NULL to ENOENT (and
> keeping any other errors)
> 
> > > 
> > > Here we miss the IS_ERR check in case info is retrieved with
> > > spi_nor_match_name().
> > > Do you expect spi_nor_match_name() to ever return an error? As it is
> > > now it doesn't.
> > > I'm fine either way. In case you want me to follow your suggestion,
> > > give me a sign
> > > and I'll make a dedicated patch to move the IS_ERR_OR_NULL check.
> > > Will add your
> > > Suggested-by tag.
> > 
> > I think it should be safe to assume it won't ever return an error since
> > all it does is iterate over an array that is always present. I don't see
> > that changing in the foreseeable future either. So I think not having
> > the IS_ERR check is fine.
> 
> But what does it cost to just add the error check now so it won't
> be forgotten in the future?
> 
>          if (name) {
>                  info = spi_nor_match_name();
>                  if (IS_ERR(info))
>                          return info;
>          }
>          if (!info)
>                   return spi_nor_read_id();
> 
>          <flash model check code follows here>
> 
> And then let the caller handle NULL and translate it to ENOENT.

Sounds good to me.

-- 
Regards,
Pratyush Yadav
Texas Instruments Inc.