mtd: onenand_base: Avoid fall-through warnings
diff mbox series

Message ID 20190522180446.GA30082@embeddedor
State New
Delegated to: Miquel Raynal
Headers show
Series
  • mtd: onenand_base: Avoid fall-through warnings
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Commit Message

Gustavo A. R. Silva May 22, 2019, 6:04 p.m. UTC
NOTICE THAT:

"...we don't know whether we need fallthroughs or breaks there and this
is just a change to avoid having new warnings when switching to
-Wimplicit-fallthrough but this change might be entirely wrong."[1]

See the original thread of discussion here:

https://lore.kernel.org/patchwork/patch/1036251/

So, in preparation to enabling -Wimplicit-fallthrough, this patch silences
the following warnings:

drivers/mtd/nand/onenand/onenand_base.c: In function ‘onenand_check_features’:
drivers/mtd/nand/onenand/onenand_base.c:3264:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
   if (ONENAND_IS_DDP(this))
      ^
drivers/mtd/nand/onenand/onenand_base.c:3284:2: note: here
  case ONENAND_DEVICE_DENSITY_2Gb:
  ^~~~
drivers/mtd/nand/onenand/onenand_base.c:3288:17: warning: this statement may fall through [-Wimplicit-fallthrough=]
   this->options |= ONENAND_HAS_UNLOCK_ALL;
drivers/mtd/nand/onenand/onenand_base.c:3290:2: note: here
  case ONENAND_DEVICE_DENSITY_1Gb:
  ^~~~

Warning level 3 was used: -Wimplicit-fallthrough=3

This patch is part of the ongoing efforts to enable
-Wimplicit-fallthrough.

[1] https://lore.kernel.org/lkml/20190509085318.34a9d4be@xps13/

Cc: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
 drivers/mtd/nand/onenand/onenand_base.c | 2 ++
 1 file changed, 2 insertions(+)

Comments

Kees Cook May 22, 2019, 9:30 p.m. UTC | #1
Sorry for being late to speaking up on this. I missed something in the
code the first time I read the thread, that now stood out to me. Notes
below...

On Wed, May 22, 2019 at 01:04:46PM -0500, Gustavo A. R. Silva wrote:
> diff --git a/drivers/mtd/nand/onenand/onenand_base.c b/drivers/mtd/nand/onenand/onenand_base.c
> index f41d76248550..6cf4df9f8c01 100644
> --- a/drivers/mtd/nand/onenand/onenand_base.c
> +++ b/drivers/mtd/nand/onenand/onenand_base.c
> @@ -3280,12 +3280,14 @@ static void onenand_check_features(struct mtd_info *mtd)

Reverse-order review, second hunk first:

>  	case ONENAND_DEVICE_DENSITY_2Gb:
>  		/* 2Gb DDP does not have 2 plane */
>  		if (!ONENAND_IS_DDP(this))
>  			this->options |= ONENAND_HAS_2PLANE;
>  		this->options |= ONENAND_HAS_UNLOCK_ALL;
> +		/* Fall through - ? */
>  
>  	case ONENAND_DEVICE_DENSITY_1Gb:
>  		/* A-Die has all block unlock */

So, I think the ONENAND_DEVICE_DENSITY_2Gb should be a "break". Though,
actually, it doesn't matter:

        case ONENAND_DEVICE_DENSITY_2Gb:
                /* 2Gb DDP does not have 2 plane */
                if (!ONENAND_IS_DDP(this))
                        this->options |= ONENAND_HAS_2PLANE;
                this->options |= ONENAND_HAS_UNLOCK_ALL;

        case ONENAND_DEVICE_DENSITY_1Gb:
                /* A-Die has all block unlock */
                if (process)
                        this->options |= ONENAND_HAS_UNLOCK_ALL;
                break;

Falling through from ONENAND_DEVICE_DENSITY_2Gb to
ONENAND_DEVICE_DENSITY_1Gb will actually have no side-effects:
ONENAND_HAS_UNLOCK_ALL was unconditionally set in ..._2Gb, so there is
no reason to fall through to ..._1Gb. (But falling through is harmless.)

Now the first hunk:

>  			if ((this->version_id & 0xf) == 0xe)
>  				this->options |= ONENAND_HAS_NOP_1;
>  		}
> +		/* Fall through - ? */
>  

        case ONENAND_DEVICE_DENSITY_4Gb:
                if (ONENAND_IS_DDP(this))
                        this->options |= ONENAND_HAS_2PLANE;
                else if (numbufs == 1) {
                        this->options |= ONENAND_HAS_4KB_PAGE;
                        this->options |= ONENAND_HAS_CACHE_PROGRAM;
                        /*
                         * There are two different 4KiB pagesize chips
                         * and no way to detect it by H/W config values.
                         *
                         * To detect the correct NOP for each chips,
                         * It should check the version ID as workaround.
                         *
                         * Now it has as following
                         * KFM4G16Q4M has NOP 4 with version ID 0x0131
                         * KFM4G16Q5M has NOP 1 with versoin ID 0x013e
                         */
                        if ((this->version_id & 0xf) == 0xe)
                                this->options |= ONENAND_HAS_NOP_1;
                }

Falling through from ONENAND_DEVICE_DENSITY_4Gb to
ONENAND_DEVICE_DENSITY_2Gb looks like it would mean that
ONENAND_HAS_2PLANE would be unconditionally set for ...4Gb, which seems
very strange to expect:

                if (ONENAND_IS_DDP(this))
                        this->options |= ONENAND_HAS_2PLANE;
...
                if (!ONENAND_IS_DDP(this))
                        this->options |= ONENAND_HAS_2PLANE;

However! This happens later:

        if (ONENAND_IS_4KB_PAGE(this))
                this->options &= ~ONENAND_HAS_2PLANE;

i.e. falling through to ...2Gb (which sets ONENAND_HAS_2PLANE) has no
effect because when ONENAND_HAS_2PLANE isn't set (numbufs == 1), it gets
_cleared_ by the above code due to ONENAND_HAS_4KB_PAGE getting set:

#define ONENAND_IS_4KB_PAGE(this) \
        (this->options & ONENAND_HAS_4KB_PAGE)


Unfortunately, though, it's less clear about ONENAND_HAS_UNLOCK_ALL,
which is getting set unconditionally for ...4Gb currently (due to the
fallthrough to ...2Gb). However, this happens later:

        if (FLEXONENAND(this)) {
                this->options &= ~ONENAND_HAS_CONT_LOCK;
                this->options |= ONENAND_HAS_UNLOCK_ALL;
        }
...
#define FLEXONENAND(this) \
        (this->device_id & DEVICE_IS_FLEXONENAND)

So it's possible this fall through has no effect (are all 4Gb density
devices also FLEXONENAND devices?)

Setting a "break" after 4Gb may remove ONENAND_HAS_UNLOCK_ALL in the
!FLEXONENAND(this) case. Does anyone have real hardware to test with?

Thoughts?
Boris Brezillon May 22, 2019, 9:37 p.m. UTC | #2
On Wed, 22 May 2019 13:04:46 -0500
"Gustavo A. R. Silva" <gustavo@embeddedor.com> wrote:

> NOTICE THAT:
> 
> "...we don't know whether we need fallthroughs or breaks there and this
> is just a change to avoid having new warnings when switching to
> -Wimplicit-fallthrough but this change might be entirely wrong."[1]
> 
> See the original thread of discussion here:
> 
> https://lore.kernel.org/patchwork/patch/1036251/
> 
> So, in preparation to enabling -Wimplicit-fallthrough, this patch silences
> the following warnings:
> 
> drivers/mtd/nand/onenand/onenand_base.c: In function ‘onenand_check_features’:
> drivers/mtd/nand/onenand/onenand_base.c:3264:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
>    if (ONENAND_IS_DDP(this))
>       ^
> drivers/mtd/nand/onenand/onenand_base.c:3284:2: note: here
>   case ONENAND_DEVICE_DENSITY_2Gb:
>   ^~~~
> drivers/mtd/nand/onenand/onenand_base.c:3288:17: warning: this statement may fall through [-Wimplicit-fallthrough=]
>    this->options |= ONENAND_HAS_UNLOCK_ALL;
> drivers/mtd/nand/onenand/onenand_base.c:3290:2: note: here
>   case ONENAND_DEVICE_DENSITY_1Gb:
>   ^~~~
> 
> Warning level 3 was used: -Wimplicit-fallthrough=3
> 
> This patch is part of the ongoing efforts to enable
> -Wimplicit-fallthrough.
> 
> [1] https://lore.kernel.org/lkml/20190509085318.34a9d4be@xps13/
> 
> Cc: Miquel Raynal <miquel.raynal@bootlin.com>
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> ---
>  drivers/mtd/nand/onenand/onenand_base.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/mtd/nand/onenand/onenand_base.c b/drivers/mtd/nand/onenand/onenand_base.c
> index f41d76248550..6cf4df9f8c01 100644
> --- a/drivers/mtd/nand/onenand/onenand_base.c
> +++ b/drivers/mtd/nand/onenand/onenand_base.c
> @@ -3280,12 +3280,14 @@ static void onenand_check_features(struct mtd_info *mtd)
>  			if ((this->version_id & 0xf) == 0xe)
>  				this->options |= ONENAND_HAS_NOP_1;
>  		}
> +		/* Fall through - ? */

So, the only thing that you'll re-use by falling through the next case
is the '->options |= ONENAND_HAS_UNLOCK_ALL' operation. I find it easier
to follow with an explicit copy of this line + a break.

>  
>  	case ONENAND_DEVICE_DENSITY_2Gb:
>  		/* 2Gb DDP does not have 2 plane */
>  		if (!ONENAND_IS_DDP(this))
>  			this->options |= ONENAND_HAS_2PLANE;
>  		this->options |= ONENAND_HAS_UNLOCK_ALL;
> +		/* Fall through - ? */

This fall through certainly doesn't make sense, as the only thing that
might be done in the 1Gb case is conditionally adding the
HAS_UNLOCK_ALL flag, and this flag is already unconditionally set.
Please add a break here.

>  
>  	case ONENAND_DEVICE_DENSITY_1Gb:
>  		/* A-Die has all block unlock */
Kees Cook May 22, 2019, 9:45 p.m. UTC | #3
On Wed, May 22, 2019 at 11:37:05PM +0200, Boris Brezillon wrote:
> > @@ -3280,12 +3280,14 @@ static void onenand_check_features(struct mtd_info *mtd)
> >  			if ((this->version_id & 0xf) == 0xe)
> >  				this->options |= ONENAND_HAS_NOP_1;
> >  		}
> > +		/* Fall through - ? */
> 
> So, the only thing that you'll re-use by falling through the next case
> is the '->options |= ONENAND_HAS_UNLOCK_ALL' operation. I find it easier
> to follow with an explicit copy of this line + a break.
> 
> >  
> >  	case ONENAND_DEVICE_DENSITY_2Gb:
> >  		/* 2Gb DDP does not have 2 plane */
> >  		if (!ONENAND_IS_DDP(this))
> >  			this->options |= ONENAND_HAS_2PLANE;
> >  		this->options |= ONENAND_HAS_UNLOCK_ALL;
> > +		/* Fall through - ? */
> 
> This fall through certainly doesn't make sense, as the only thing that
> might be done in the 1Gb case is conditionally adding the
> HAS_UNLOCK_ALL flag, and this flag is already unconditionally set.
> Please add a break here.
> 
> >  
> >  	case ONENAND_DEVICE_DENSITY_1Gb:
> >  		/* A-Die has all block unlock */
> 

Your reply was much more to-the-point than mine. :) I'd agree: retain
existing behavior (ONENAND_HAS_UNLOCK_ALL) and add breaks.
Boris Brezillon May 22, 2019, 9:57 p.m. UTC | #4
On Wed, 22 May 2019 14:30:11 -0700
Kees Cook <keescook@chromium.org> wrote:

> Sorry for being late to speaking up on this. I missed something in the
> code the first time I read the thread, that now stood out to me. Notes
> below...
> 
> On Wed, May 22, 2019 at 01:04:46PM -0500, Gustavo A. R. Silva wrote:
> > diff --git a/drivers/mtd/nand/onenand/onenand_base.c b/drivers/mtd/nand/onenand/onenand_base.c
> > index f41d76248550..6cf4df9f8c01 100644
> > --- a/drivers/mtd/nand/onenand/onenand_base.c
> > +++ b/drivers/mtd/nand/onenand/onenand_base.c
> > @@ -3280,12 +3280,14 @@ static void onenand_check_features(struct mtd_info *mtd)  
> 
> Reverse-order review, second hunk first:
> 
> >  	case ONENAND_DEVICE_DENSITY_2Gb:
> >  		/* 2Gb DDP does not have 2 plane */
> >  		if (!ONENAND_IS_DDP(this))
> >  			this->options |= ONENAND_HAS_2PLANE;
> >  		this->options |= ONENAND_HAS_UNLOCK_ALL;
> > +		/* Fall through - ? */
> >  
> >  	case ONENAND_DEVICE_DENSITY_1Gb:
> >  		/* A-Die has all block unlock */  
> 
> So, I think the ONENAND_DEVICE_DENSITY_2Gb should be a "break". Though,
> actually, it doesn't matter:
> 
>         case ONENAND_DEVICE_DENSITY_2Gb:
>                 /* 2Gb DDP does not have 2 plane */
>                 if (!ONENAND_IS_DDP(this))
>                         this->options |= ONENAND_HAS_2PLANE;
>                 this->options |= ONENAND_HAS_UNLOCK_ALL;
> 
>         case ONENAND_DEVICE_DENSITY_1Gb:
>                 /* A-Die has all block unlock */
>                 if (process)
>                         this->options |= ONENAND_HAS_UNLOCK_ALL;
>                 break;
> 
> Falling through from ONENAND_DEVICE_DENSITY_2Gb to
> ONENAND_DEVICE_DENSITY_1Gb will actually have no side-effects:
> ONENAND_HAS_UNLOCK_ALL was unconditionally set in ..._2Gb, so there is
> no reason to fall through to ..._1Gb. (But falling through is harmless.)
> 
> Now the first hunk:
> 
> >  			if ((this->version_id & 0xf) == 0xe)
> >  				this->options |= ONENAND_HAS_NOP_1;
> >  		}
> > +		/* Fall through - ? */
> >    
> 
>         case ONENAND_DEVICE_DENSITY_4Gb:
>                 if (ONENAND_IS_DDP(this))
>                         this->options |= ONENAND_HAS_2PLANE;
>                 else if (numbufs == 1) {
>                         this->options |= ONENAND_HAS_4KB_PAGE;
>                         this->options |= ONENAND_HAS_CACHE_PROGRAM;
>                         /*
>                          * There are two different 4KiB pagesize chips
>                          * and no way to detect it by H/W config values.
>                          *
>                          * To detect the correct NOP for each chips,
>                          * It should check the version ID as workaround.
>                          *
>                          * Now it has as following
>                          * KFM4G16Q4M has NOP 4 with version ID 0x0131
>                          * KFM4G16Q5M has NOP 1 with versoin ID 0x013e
>                          */
>                         if ((this->version_id & 0xf) == 0xe)
>                                 this->options |= ONENAND_HAS_NOP_1;
>                 }
> 
> Falling through from ONENAND_DEVICE_DENSITY_4Gb to
> ONENAND_DEVICE_DENSITY_2Gb looks like it would mean that
> ONENAND_HAS_2PLANE would be unconditionally set for ...4Gb, which seems
> very strange to expect:
> 
>                 if (ONENAND_IS_DDP(this))
>                         this->options |= ONENAND_HAS_2PLANE;
> ...
>                 if (!ONENAND_IS_DDP(this))
>                         this->options |= ONENAND_HAS_2PLANE;

Oops, didn't notice the ! on the second test.

> 
> However! This happens later:
> 
>         if (ONENAND_IS_4KB_PAGE(this))
>                 this->options &= ~ONENAND_HAS_2PLANE;
> 
> i.e. falling through to ...2Gb (which sets ONENAND_HAS_2PLANE) has no
> effect because when ONENAND_HAS_2PLANE isn't set (numbufs == 1), it gets
> _cleared_ by the above code due to ONENAND_HAS_4KB_PAGE getting set:

Are you sure !DDP implies num_bufs == 1?


> 
> #define ONENAND_IS_4KB_PAGE(this) \
>         (this->options & ONENAND_HAS_4KB_PAGE)
> 
> 
> Unfortunately, though, it's less clear about ONENAND_HAS_UNLOCK_ALL,
> which is getting set unconditionally for ...4Gb currently (due to the
> fallthrough to ...2Gb). However, this happens later:
> 
>         if (FLEXONENAND(this)) {
>                 this->options &= ~ONENAND_HAS_CONT_LOCK;
>                 this->options |= ONENAND_HAS_UNLOCK_ALL;
>         }
> ...
> #define FLEXONENAND(this) \
>         (this->device_id & DEVICE_IS_FLEXONENAND)
> 
> So it's possible this fall through has no effect (are all 4Gb density
> devices also FLEXONENAND devices?)
> 

All this look suspicious, and even if the fall through logic
has no side effects in practice (which I'm still not sure is the case),
I think it'd be better to explicitly set the flags that have
to be set in each case statement and add breaks.
Kees Cook May 22, 2019, 10:20 p.m. UTC | #5
On Wed, May 22, 2019 at 11:57:38PM +0200, Boris Brezillon wrote:
> All this look suspicious, and even if the fall through logic
> has no side effects in practice (which I'm still not sure is the case),
> I think it'd be better to explicitly set the flags that have
> to be set in each case statement and add breaks.

Yeah, totally agreed. :)
Gustavo A. R. Silva May 22, 2019, 10:30 p.m. UTC | #6
On 5/22/19 5:20 PM, Kees Cook wrote:
> On Wed, May 22, 2019 at 11:57:38PM +0200, Boris Brezillon wrote:
>> All this look suspicious, and even if the fall through logic
>> has no side effects in practice (which I'm still not sure is the case),
>> I think it'd be better to explicitly set the flags that have
>> to be set in each case statement and add breaks.
> 
> Yeah, totally agreed. :)
> 

Thank you, Kees and Boris for the feedback. Some external opinions were
certainly much needed here.

I'll just wait for any comments from the MTD guys.

Thanks
--
Gustavo

Patch
diff mbox series

diff --git a/drivers/mtd/nand/onenand/onenand_base.c b/drivers/mtd/nand/onenand/onenand_base.c
index f41d76248550..6cf4df9f8c01 100644
--- a/drivers/mtd/nand/onenand/onenand_base.c
+++ b/drivers/mtd/nand/onenand/onenand_base.c
@@ -3280,12 +3280,14 @@  static void onenand_check_features(struct mtd_info *mtd)
 			if ((this->version_id & 0xf) == 0xe)
 				this->options |= ONENAND_HAS_NOP_1;
 		}
+		/* Fall through - ? */
 
 	case ONENAND_DEVICE_DENSITY_2Gb:
 		/* 2Gb DDP does not have 2 plane */
 		if (!ONENAND_IS_DDP(this))
 			this->options |= ONENAND_HAS_2PLANE;
 		this->options |= ONENAND_HAS_UNLOCK_ALL;
+		/* Fall through - ? */
 
 	case ONENAND_DEVICE_DENSITY_1Gb:
 		/* A-Die has all block unlock */