RE: [PATCH 1/2] Staging: fsl-mc: include: mc: Kernel type 's16' preferred over 'int16_t'

[Stuart Yoder]

> -----Original Message-----
> From: Dan Carpenter [mailto:dan.carpenter@xxxxxxxxxx]
> Sent: Friday, November 11, 2016 5:23 AM
> To: Shiva Kerdel <shiva@xxxxxxxx>
> Cc: Stuart Yoder <stuart.yoder@xxxxxxx>; devel@xxxxxxxxxxxxxxxxxxxx; German.Rivera@xxxxxxxxxxxxx;
> gregkh@xxxxxxxxxxxxxxxxxxx; Nipun Gupta <nipun.gupta@xxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; German
> Rivera <german.rivera@xxxxxxx>; treding@xxxxxxxxxx; itai.katz@xxxxxxx
> Subject: Re: [PATCH 1/2] Staging: fsl-mc: include: mc: Kernel type 's16' preferred over 'int16_t'
> 
> On Fri, Nov 11, 2016 at 12:07:39PM +0100, Shiva Kerdel wrote:
> > Follow the kernel type preferrences of using 's16' over 'int16_t'.
> >
> > Signed-off-by: Shiva Kerdel <shiva@xxxxxxxx>
> > Acked-by: Stuart Yoder <stuart.yoder@xxxxxxx>
> > ---
> > Changes for v2:
> >     - corrected an error in the log message, wrote 's32' instead of 's16'.
> > Changes for v3:
> >     - added the missing annotates.
> > Changes for v4:
> >     - corrected patch subject to version 4.
> >
> >  drivers/staging/fsl-mc/include/mc-bus.h | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/staging/fsl-mc/include/mc-bus.h b/drivers/staging/fsl-mc/include/mc-bus.h
> > index e915574..c7cad87 100644
> > --- a/drivers/staging/fsl-mc/include/mc-bus.h
> > +++ b/drivers/staging/fsl-mc/include/mc-bus.h
> > @@ -42,8 +42,8 @@ struct msi_domain_info;
> >   */
> >  struct fsl_mc_resource_pool {
> >  	enum fsl_mc_pool_type type;
> > -	int16_t max_count;
> > -	int16_t free_count;
> > +	s16 max_count;
> 
> My understanding is that this has to be signed because the design of
> this driver is that we keep adding devices until the the counter
> overflows.  After that there are a couple tests for
> "if (WARN_ON(res_pool->max_count < 0)) " which prevent the driver from
> working again.
>
> This all seems pretty horrible.

Can you elaborate?

The resource pools managed by this driver are populated by hardware objects
discovered when the fsl-mc bus probes a DPRC/container.

The number of potential objects discovered of a given type is in the hundreds,
so a signed 16-bit number is order of magnitudes larger than anything we will
ever encounter.

Would you feel better about this if max_count was an int?

The max_count reflects the total number of objects discovered.  If that is
exceeded we display a warning, because something is horribly wrong.  Nothing
stops working, the allocator simply refuses to add anything else to the
free list.

The only reason max_count is there at all is as an internal check against
bugs and resource leaks.  If the driver is being removed and a resource
pool is being freed, max_count must be zero...i.e. all objects should have
been removed.  If not, there is a leak somewhere.  So, it's a sanity check.

Thanks,
Stuart