linux-kernel - Re: [PATCH] vme: 8-bit status/id takes 256 values, not 255

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Date:	Sun, 18 Oct 2015 19:22:39 +0100
From:	Martyn Welch <martyn@...chs.me.uk>
To:	Dmitry Kalinkin <dmitry.kalinkin@...il.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Manohar Vanga <manohar.vanga@...il.com>,
	devel@...verdev.osuosl.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] vme: 8-bit status/id takes 256 values, not 255



On 18/10/15 18:07, Dmitry Kalinkin wrote:
> On Sun, Oct 18, 2015 at 9:30 AM, Martyn Welch <martyn@...chs.me.uk> wrote:
>> On 10 October 2015 at 23:00, Dmitry Kalinkin <dmitry.kalinkin@...il.com> wrote:
>>> Fixes an off by one array size.
>>>
>> The Status/ID is an 8-bit value (OK, the standard states it can be a
>> 8, 16 or 32-bit value, however both of the chipsets we support at this
>> point in time support an 8-bit value), why do we need a 256th entry in
>> the array?
> Hi Martyn,
>
> 8 bit signal spans 256 values from 8'b0000_0000 to 8'b1111_1111.
> In order to serve that we need a C array of size 256.
> callback[255]; in the original code means that array has 255 elements
> with indices from 0 to 254, there would be no way to register callback
> for a valid Status/ID value of 255 (aka 8'b1111_1111). For that we
> need a 256th element.

Err, yep. (Curses self for being so stupid.)

Signed-off-by: Martyn Welch <martyn@...chs.me.uk>

> Dmitri
>
>> Martyn
>>
>>> Signed-off-by: Dmitry Kalinkin <dmitry.kalinkin@...il.com>
>>> ---
>>>   drivers/vme/vme_bridge.h | 4 +++-
>>>   include/linux/vme.h      | 3 +++
>>>   2 files changed, 6 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/vme/vme_bridge.h b/drivers/vme/vme_bridge.h
>>> index 397578a..b59cbee 100644
>>> --- a/drivers/vme/vme_bridge.h
>>> +++ b/drivers/vme/vme_bridge.h
>>> @@ -1,6 +1,8 @@
>>>   #ifndef _VME_BRIDGE_H_
>>>   #define _VME_BRIDGE_H_
>>>
>>> +#include <linux/vme.h>
>>> +
>>>   #define VME_CRCSR_BUF_SIZE (508*1024)
>>>   /*
>>>    * Resource structures
>>> @@ -91,7 +93,7 @@ struct vme_callback {
>>>
>>>   struct vme_irq {
>>>          int count;
>>> -       struct vme_callback callback[255];
>>> +       struct vme_callback callback[VME_NUM_STATUSID];
>>>   };
>>>
>>>   /* Allow 16 characters for name (including null character) */
>>> diff --git a/include/linux/vme.h b/include/linux/vme.h
>>> index c013135..71e4a6d 100644
>>> --- a/include/linux/vme.h
>>> +++ b/include/linux/vme.h
>>> @@ -81,6 +81,9 @@ struct vme_resource {
>>>
>>>   extern struct bus_type vme_bus_type;
>>>
>>> +/* Number of VME interrupt vectors */
>>> +#define VME_NUM_STATUSID       256
>>> +
>>>   /* VME_MAX_BRIDGES comes from the type of vme_bus_numbers */
>>>   #define VME_MAX_BRIDGES                (sizeof(unsigned int)*8)
>>>   #define VME_MAX_SLOTS          32
>>> --
>>> 1.8.3.1
>>>

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