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Subject: Re: [RFC PATCH v2 1/1] iio/scmi: Adding support for IIO SCMI Based
 Sensors
To:     Jonathan Cameron <jic23@kernel.org>,
        Jyoti Bhayana <jbhayana@google.com>
Cc:     Hartmut Knaack <knaack.h@gmx.de>,
        Peter Meerwald-Stadler <pmeerw@pmeerw.net>,
        Mauro Carvalho Chehab <mchehab+huawei@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Rob Herring <robh@kernel.org>,
        Lukas Bulwahn <lukas.bulwahn@gmail.com>,
        linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org,
        cristian.marussi@arm.com, sudeep.holla@arm.com,
        egranata@google.com, mikhail.golubev@opensynergy.com,
        Igor.Skalkin@opensynergy.com, Peter.hilber@opensynergy.com,
        ankitarora@google.com
References: <20201224031921.1547519-1-jbhayana@google.com>
 <20201224031921.1547519-2-jbhayana@google.com>
 <20201230134104.48d07ff5@archlinux>
From:   Lars-Peter Clausen <lars@metafoo.de>
Message-ID: <220be27a-8eef-8582-9a8c-270f16fda688@metafoo.de>
Date:   Wed, 30 Dec 2020 17:09:54 +0100
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On 12/30/20 2:41 PM, Jonathan Cameron wrote:
> On Thu, 24 Dec 2020 03:19:21 +0000
> Jyoti Bhayana <jbhayana@google.com> wrote:
>
>> +	/*
>> +	 * The seconds field in the sensor interval in SCMI is 16 bits long
>> +	 * Therefore seconds  = 1/Hz <= 0xFFFF. As floating point calculations are
>> +	 * discouraged in the kernel driver code, to calculate the scale factor (sf)
>> +	 * (1* 1000000 * sf)/uHz <= 0xFFFF. Therefore, sf <= (uHz * 0xFFFF)/1000000
>> +	 *  To calculate the multiplier,we convert the sf into char string  and
>> +	 *  count the number of characters
>> +	 */
>> +
>> +	mult = scnprintf(buf, 32, "%llu", ((u64)uHz * 0xFFFF) / UHZ_PER_HZ) - 1;
> use sizeof(buf) instead of having 32 again.
>
Since this is just interested in the number of characters and not the 
string itself I believe it is possible to just call sprintf with NULL 
instead of a buffer. It will then still return the number of characters, 
but not print anything.

But maybe providing a ilog10() helper is the better approach.