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SubjectRe: [PATCH 0/3] mtd: core: protect access to mtd devices while in suspend
Hi Boris,

boris.brezillon@collabora.com wrote on Wed, 20 Oct 2021 09:00:58 +0200:

> On Wed, 20 Oct 2021 08:52:50 +0200
> Boris Brezillon <boris.brezillon@collabora.com> wrote:
>
> > On Tue, 19 Oct 2021 20:08:00 +0200
> > Sean Nyekjaer <sean@geanix.com> wrote:
> >
> > > On Fri, Oct 15, 2021 at 08:22:06AM +0200, Miquel Raynal wrote:
> > > > Hi Sean,
> > > >
> > > > boris.brezillon@collabora.com wrote on Mon, 11 Oct 2021 16:05:46 +0200:
> > > >
> > > > > On Mon, 11 Oct 2021 13:52:50 +0200
> > >
> > > [ ... ]
> > >
> > > >
> > > > > > One (small) issue still present. gpmi_nand.c uses the rwsem before it's
> > > > > > initialized. Seems cumbersome to have every mtd/nand driver to call
> > > > > > init_waitqueue_head() and init_rwsem(). Could we somehow move the call
> > > > > > to mtd_set_dev_defaults() before nand_create_bbt()?
> > > > >
> > > > > I have a nasty trick for that one, but I'm not sure Miquel will like it
> > > > > (actually, I don't like it either, but it's so simple compared to the
> > > > > other options we have that I'm tempted to go for this approach until
> > > > > someone has time to invest in a cleaner solution :-)):
> > > > >
> > > > > diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
> > > > > index 3d6c6e880520..a9ac2d528a4d 100644
> > > > > --- a/drivers/mtd/nand/raw/nand_base.c
> > > > > +++ b/drivers/mtd/nand/raw/nand_base.c
> > > > > @@ -6222,8 +6222,6 @@ static int nand_scan_tail(struct nand_chip *chip)
> > > > > mtd->_sync = nand_sync;
> > > > > mtd->_lock = nand_lock;
> > > > > mtd->_unlock = nand_unlock;
> > > > > - mtd->_suspend = nand_suspend;
> > > > > - mtd->_resume = nand_resume;
> > > > > mtd->_reboot = nand_shutdown;
> > > > > mtd->_block_isreserved = nand_block_isreserved;
> > > > > mtd->_block_isbad = nand_block_isbad;
> > > > > @@ -6269,6 +6267,13 @@ static int nand_scan_tail(struct nand_chip *chip)
> > > > > if (ret)
> > > > > goto err_free_secure_regions;
> > > > >
> > > > > + /*
> > > > > + * Populate the suspend/resume hooks after the BBT has been scanned to
> > > > > + * avoid using the suspend lock and resume waitqueue which are only
> > > > > + * initialized when mtd_device_register() is called.
> > > > > + */
> > > > > + mtd->_suspend = nand_suspend;
> > > > > + mtd->_resume = nand_resume;
> > > > > return 0;
> > > >
> > > > I'm fine with this as long as it is documented for now.
> > > >
> > >
> > > Hi Boris and Miquel,
> > >
> > > gpmi-nand.c sets NAND_SKIP_BBTSCAN so we won't get there and populate
> > > suspend resume hooks :(
> > > Guess there is other drivers that does the same thing...
> >
> > This should fix the issue:
> >
> > diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
> > index 3d6c6e880520..c92b17f66994 100644
> > --- a/drivers/mtd/nand/raw/nand_base.c
> > +++ b/drivers/mtd/nand/raw/nand_base.c
> > @@ -6222,8 +6222,6 @@ static int nand_scan_tail(struct nand_chip *chip)
> > mtd->_sync = nand_sync;
> > mtd->_lock = nand_lock;
> > mtd->_unlock = nand_unlock;
> > - mtd->_suspend = nand_suspend;
> > - mtd->_resume = nand_resume;
> > mtd->_reboot = nand_shutdown;
> > mtd->_block_isreserved = nand_block_isreserved;
> > mtd->_block_isbad = nand_block_isbad;
> > @@ -6262,13 +6260,21 @@ static int nand_scan_tail(struct nand_chip *chip)
> >
> > /* Check, if we should skip the bad block table scan */
> > if (chip->options & NAND_SKIP_BBTSCAN)
> > - return 0;
> > + goto out;
> >
> > /* Build bad block table */
> > ret = nand_create_bbt(chip);
> > if (ret)
> > goto err_free_secure_regions;
> >
> > +out:
> > + /*
> > + * Populate the suspend/resume hooks after the BBT has been scanned to
> > + * avoid using the suspend lock and resume waitqueue which are only
> > + * initialized when mtd_device_register() is called.
> > + */
> > + mtd->_suspend = nand_suspend;
> > + mtd->_resume = nand_resume;
> > return 0;
> >
> > err_free_secure_regions:
>
> Actually, this version is even cleaner:
>
> diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
> index 3d6c6e880520..98c39b7f6279 100644
> --- a/drivers/mtd/nand/raw/nand_base.c
> +++ b/drivers/mtd/nand/raw/nand_base.c
> @@ -6222,8 +6222,6 @@ static int nand_scan_tail(struct nand_chip *chip)
> mtd->_sync = nand_sync;
> mtd->_lock = nand_lock;
> mtd->_unlock = nand_unlock;
> - mtd->_suspend = nand_suspend;
> - mtd->_resume = nand_resume;
> mtd->_reboot = nand_shutdown;
> mtd->_block_isreserved = nand_block_isreserved;
> mtd->_block_isbad = nand_block_isbad;
> @@ -6261,14 +6259,20 @@ static int nand_scan_tail(struct nand_chip *chip)
> goto err_free_interface_config;
>
> /* Check, if we should skip the bad block table scan */
> - if (chip->options & NAND_SKIP_BBTSCAN)
> - return 0;
> -
> - /* Build bad block table */
> - ret = nand_create_bbt(chip);
> - if (ret)
> - goto err_free_secure_regions;
> + if (chip->options & NAND_SKIP_BBTSCAN) {
> + /* Build bad block table */
> + ret = nand_create_bbt(chip);
> + if (ret)
> + goto err_free_secure_regions;
> + }

Nice idea.

>
> + /*
> + * Populate the suspend/resume hooks after the BBT has been scanned to
> + * avoid using the suspend lock and resume waitqueue which are only
> + * initialized when mtd_device_register() is called.
> + */
> + mtd->_suspend = nand_suspend;
> + mtd->_resume = nand_resume;
> return 0;
>
> err_free_secure_regions:

Cheers,
Miquèl

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