[PATCH 3/5] env: sf: Preserve and free the previous flash

[Pratyush Yadav]

On 18/05/20 05:36PM, Jagan Teki wrote:
> On Fri, May 15, 2020 at 2:19 PM Pratyush Yadav <p.yadav at ti.com> wrote:
> >
> > On 15/05/20 01:14PM, Jagan Teki wrote:
> > > On Fri, May 15, 2020 at 12:54 PM Pratyush Yadav <p.yadav at ti.com> wrote:
> > > >
> > > > Hi Jagan,
> > > >
> > > > On 14/05/20 05:41PM, Jagan Teki wrote:
> > > > > env_flash is a global flash pointer, and the probe would
> > > > > happen only if env_flash is NULL, but there is no checking
> > > > > and free the pointer if is not NULL.
> > > > >
> > > > > So, this patch frees the env_flash if it's not NULL, and
> > > > > get the probed flash in new flash pointer and finally
> > > > > assign into env_flash.
> > > > >
> > > > > Note: Similar approach has been followed and tested in
> > > > > cmd/sf.c
> > > > >
> > > > > Cc: Simon Glass <sjg at chromium.org>
> > > > > Cc: Vignesh R <vigneshr at ti.com>
> > > > > Signed-off-by: Jagan Teki <jagan at amarulasolutions.com>
> > > > > ---
> > > > >  env/sf.c | 18 ++++++++++--------
> > > > >  1 file changed, 10 insertions(+), 8 deletions(-)
> > > > >
> > > > > diff --git a/env/sf.c b/env/sf.c
> > > > > index 64c57f2cdf..af59c8375c 100644
> > > > > --- a/env/sf.c
> > > > > +++ b/env/sf.c
> > > > > @@ -50,15 +50,17 @@ static int setup_flash_device(void)
> > > > >
> > > > >       env_flash = dev_get_uclass_priv(new);
> > > > >  #else
> > > > > +     struct spi_flash *new;
> > > > >
> > > > > -     if (!env_flash) {
> > > > > -             env_flash = spi_flash_probe(CONFIG_ENV_SPI_BUS,
> > > > > -                     CONFIG_ENV_SPI_CS,
> > > > > -                     CONFIG_ENV_SPI_MAX_HZ, CONFIG_ENV_SPI_MODE);
> > > > > -             if (!env_flash) {
> > > > > -                     env_set_default("spi_flash_probe() failed", 0);
> > > > > -                     return -EIO;
> > > > > -             }
> > > > > +     if (env_flash)
> > > > > +             spi_flash_free(env_flash);
> > > > > +
> > > > > +     new = spi_flash_probe(CONFIG_ENV_SPI_BUS, CONFIG_ENV_SPI_CS,
> > > >
> > > > Why not assign env_flash directly here? You do it in the very next
> > > > statement anyway. I don't think the extra 'new' variable is needed.
> > >
> > > If flash pointer is used free it, before probing a new flash and
> > > storing it in flash.
> >
> > Understood.
> >
> > > In this scenario it requires local new pointer,
> > > it was known observation we have faced in cmd/sf.c
> >
> > What difference does using the local pointer make though? We don't do
> > anything with it. We just assign it to env_flash in the next statement.
> > This is similar to doing:
> >
> >   a = foo();
> >   b = a;
> >   if (a)
> >         ...
> >
> > The below snippet is equivalent:
> >
> >   b = foo();
> >   if (b)
> >         ...
> >
> > We can get rid of 'a' this way.
> 
> The scenario here, seems different here we need to take care of free
> the old pointer and update new pointer with a global pointer like
> below.
> 
> if (b)
>     free(b);
> a = foo();
> b = a;
> if (!a)
>    fail;
> 
> So, you mean to say as below?
> 
> if (b)
>     free(b);
> b = foo();
> if (!b)
>      fail;

Yes, I mean this. Since the pointer b is freed/unassigned, the old 
pointer value is of no use to us. Getting rid of a (or new in case of 
this patch) makes the code a bit cleaner.

-- 
Regards,
Pratyush Yadav
Texas Instruments India