From: Lars-Peter Clausen <lars@metafoo.de>
To: Muhammad Usama Anjum <usama.anjum@collabora.com>,
Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Michael Hennerich <Michael.Hennerich@analog.com>,
Jonathan Cameron <jic23@kernel.org>,
Mihail Chindris <mihail.chindris@analog.com>,
"open list:IIO SUBSYSTEM AND DRIVERS" <linux-iio@vger.kernel.org>,
open list <linux-kernel@vger.kernel.org>,
Collabora Kernel ML <kernel@collabora.com>,
kernel-janitors <kernel-janitors@vger.kernel.org>
Subject: Re: [PATCH] drivers:iio:dac make expression evaluation 64-bit
Date: Thu, 23 Dec 2021 17:38:19 +0100 [thread overview]
Message-ID: <16f84d86-4135-8a19-c5e1-3fbe8db78947@metafoo.de> (raw)
In-Reply-To: <eb59f405-24c6-69b8-beb1-465bfb783f61@collabora.com>
On 12/23/21 5:34 PM, Muhammad Usama Anjum wrote:
> On 12/22/21 11:49 PM, Andy Shevchenko wrote:
>> On Wed, Dec 22, 2021 at 5:59 PM Muhammad Usama Anjum
>> <usama.anjum@collabora.com> wrote:
>>> Two 32-bit values are being evaluated using 32-bit arithmetic and then
>>> passed to s64 type. It is wrong. Expression should be evaluated using
>>> 64-bit arithmetic and then passed.
>> ...
>>
>>> dac->ch_data[ch].scale_dec = DIV_ROUND_CLOSEST((s64)rem * 1000000,
>>> 65536);
>> Shouldn't the above be fixed as well? Has anybody tried to compile on
>> 32-bit arch this?
> No, it correct already. In this case, rem is being typecasted to s64 and
> then multiplied with a 32-bit number, 1000000. Thus 64-bit arithmetic is
> being performed here.
What Andy means is that this needs to be DIV_S64_ROUND_CLOSEST() to work
on 32-bit platforms. But it is clearly unrelated to your change and
should be in its own patch.
next prev parent reply other threads:[~2021-12-23 16:38 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-21 19:20 [PATCH] drivers:iio:dac make expression evaluation 64-bit Muhammad Usama Anjum
2021-12-22 18:49 ` Andy Shevchenko
2021-12-23 16:34 ` Muhammad Usama Anjum
2021-12-23 16:38 ` Lars-Peter Clausen [this message]
2022-01-04 10:28 ` Chindris, Mihail
2022-01-05 13:39 ` Dan Carpenter
2022-01-05 15:36 ` Sa, Nuno
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