From: vipin.kumar@st•com (Vipin Kumar)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 09/11] fsmc/nand:FIX: replace change_bit routine
Date: Thu, 11 Oct 2012 09:47:03 +0530 [thread overview]
Message-ID: <5076483F.5000102@st.com> (raw)
In-Reply-To: <alpine.LFD.2.02.1210101559250.16518@xanadu.home>
On 10/11/2012 1:51 AM, Nicolas Pitre wrote:
> On Wed, 10 Oct 2012, Linus Walleij wrote:
>
>> On Tue, Oct 9, 2012 at 12:44 PM, Vipin Kumar<vipin.kumar@st•com> wrote:
>>
>>> change_bit routine accepts only ulong pointers as buffer, so an unaligned char
>>> pointer passed to change_bit may lead to a crash.
>>>
>>> Fix this bug by accessing the buffer as char pointer.
>>
>> Why not see if we can fix change_bit() instead?
>> Since I suspect this is on ARM I bet Russell and Nico
>> want to hear about this if there is a problem.
>>
>> Can the ARM change_bit() not be fixed, so that
>> long arguments are the only option?
>
Hello Nicolas
> No. It is this code which is totally broken.
>
Yes, I understand and accept the probelm. That's why the fix
> The change_bit() is defined to operate on long values, in the _native_
> endian. Now imagine what this is going to do to your data buffer if
> instead you are running on a big endian device.
>
> And I doubt there is anything requiring atomic bit manipulation here
> either.
>
No, there is no requirement for an atomic change_bit
>>> if (err_idx[i]< chip->ecc.size * 8) {
>>> - change_bit(err_idx[i], (unsigned long *)dat);
>>> + uint8_t *p = dat + err_idx[i] / 8;
>>> + *p = *p ^ (1<< (err_idx[i] % 8));
>>
>> I'm one of these people who would write>>3 and
>> &7 rather than /8 or %8 but I guess we are all
>> different. Atleast consider it if you stick with this...
>
> Better yet:
>
> dat[err_idx[i] / 8] ^= (1<< (err_idx[i] % 8));
>
> The /8 and %8 will be changed into>>3 and&7 by the compiler anyway,
> while the /8 and %8 form is possibly a bit less obscure.
>
Yes, that's exactly why I kept /8 and %8. I would change the code as
suggested by you
> Of course, this needs to be done over _all_ this driver, not only a few
> cases.
>
There is only one place which needs a change_bit. I would send a v2 with
the suggested change
Vipin
>
> Nicolas
> .
>
next prev parent reply other threads:[~2012-10-11 4:17 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-09 10:44 [PATCH 00/11] mtd/nand: fsmc driver updates Vipin Kumar
2012-10-09 10:44 ` [PATCH 01/11] fsmc/nand:FIX: Change the type for regs to void __iomem * Vipin Kumar
2012-10-09 17:14 ` viresh kumar
2012-10-10 16:49 ` Linus Walleij
2012-10-17 12:30 ` Artem Bityutskiy
2012-10-09 10:44 ` [PATCH 02/11] fsmc/nand: Rearrange the fsmc_nand_data structure and update comments Vipin Kumar
2012-10-09 11:52 ` Jean-Christophe PLAGNIOL-VILLARD
2012-10-11 4:24 ` Vipin Kumar
2012-10-09 17:15 ` viresh kumar
2012-10-09 10:44 ` [PATCH 03/11] fsmc/nand: Support multiple banks connected to controller Vipin Kumar
2012-10-09 11:55 ` Jean-Christophe PLAGNIOL-VILLARD
2012-10-10 10:28 ` Vipin Kumar
2012-10-17 12:31 ` Artem Bityutskiy
2012-10-09 10:44 ` [PATCH 04/11] fsmc/nand: Accept nand timing parameters via DT Vipin Kumar
2012-10-09 11:57 ` Jean-Christophe PLAGNIOL-VILLARD
2012-10-11 4:25 ` Vipin Kumar
2012-10-09 17:20 ` viresh kumar
2012-10-09 10:44 ` [PATCH 05/11] fsmc: Implement ready/busy through gpio pin Vipin Kumar
2012-10-09 11:59 ` Jean-Christophe PLAGNIOL-VILLARD
2012-10-09 17:34 ` viresh kumar
2012-10-09 10:44 ` [PATCH 06/11] fsmc/nand: Modify the wait to uninterruptible Vipin Kumar
2012-10-10 17:10 ` Linus Walleij
2012-10-17 12:47 ` Artem Bityutskiy
2012-10-09 10:44 ` [PATCH 07/11] fsmc/nand: Provide contiguous buffers to dma Vipin Kumar
2012-10-09 17:41 ` viresh kumar
2012-10-10 17:07 ` Linus Walleij
2012-10-11 3:16 ` viresh kumar
2012-10-11 4:07 ` Vipin Kumar
2012-10-11 4:08 ` Vipin Kumar
2012-10-11 4:15 ` viresh kumar
2012-10-11 16:06 ` Linus Walleij
2012-10-11 17:07 ` viresh kumar
2012-10-11 21:51 ` Linus Walleij
2012-10-12 3:55 ` Vipin Kumar
2012-10-15 13:18 ` Artem Bityutskiy
2012-10-15 16:27 ` Brian Norris
2012-10-15 19:51 ` Linus Walleij
2012-10-16 7:14 ` Artem Bityutskiy
2012-10-16 10:05 ` Linus Walleij
2012-10-21 7:38 ` Brian Norris
2012-10-21 11:00 ` Artem Bityutskiy
2012-10-21 12:02 ` Artem Bityutskiy
2012-10-16 7:11 ` Artem Bityutskiy
2012-10-21 7:21 ` Brian Norris
2012-10-09 10:44 ` [PATCH 08/11] fsmc/nand: Use relaxed variants of io accessors Vipin Kumar
2012-10-09 17:42 ` viresh kumar
2012-10-10 17:09 ` Linus Walleij
2012-10-09 10:44 ` [PATCH 09/11] fsmc/nand:FIX: replace change_bit routine Vipin Kumar
2012-10-10 17:22 ` Linus Walleij
2012-10-10 20:21 ` Nicolas Pitre
2012-10-11 4:17 ` Vipin Kumar [this message]
2012-10-10 20:45 ` Russell King - ARM Linux
2012-10-11 4:20 ` Vipin Kumar
2012-10-09 10:44 ` [PATCH 10/11] fsmc/nand: Add sw bch support for ecc calculation/correction Vipin Kumar
2012-10-09 11:50 ` Jean-Christophe PLAGNIOL-VILLARD
2012-10-10 10:33 ` Vipin Kumar
2012-10-09 10:44 ` [PATCH 11/11] nand: Increase the ecc placement locations to 640 Vipin Kumar
2012-10-17 12:47 ` Artem Bityutskiy
2012-10-18 6:36 ` Brian Norris
2012-10-17 12:48 ` [PATCH 00/11] mtd/nand: fsmc driver updates Artem Bityutskiy
2012-10-18 4:13 ` Vipin Kumar
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