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Date: Fri, 11 Nov 2016 14:52:31 +0000
From: Stuart Yoder <stuart.yoder@....com>
To: Dan Carpenter <dan.carpenter@...cle.com>,
Shiva Kerdel <shiva@...ev.nl>
CC: "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
Nipun Gupta <nipun.gupta@....com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"treding@...dia.com" <treding@...dia.com>,
Laurentiu Tudor <laurentiu.tudor@....com>
Subject: RE: [PATCH 1/2] Staging: fsl-mc: include: mc: Kernel type 's16'
preferred over 'int16_t'
> -----Original Message-----
> From: Dan Carpenter [mailto:dan.carpenter@...cle.com]
> Sent: Friday, November 11, 2016 5:23 AM
> To: Shiva Kerdel <shiva@...ev.nl>
> Cc: Stuart Yoder <stuart.yoder@....com>; devel@...verdev.osuosl.org; German.Rivera@...escale.com;
> gregkh@...uxfoundation.org; Nipun Gupta <nipun.gupta@....com>; linux-kernel@...r.kernel.org; German
> Rivera <german.rivera@....com>; treding@...dia.com; itai.katz@....com
> 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@...ev.nl>
> > Acked-by: Stuart Yoder <stuart.yoder@....com>
> > ---
> > 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
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