linux-kernel - Re: Export clocks_calc_mult

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Date:	Wed, 30 Mar 2016 12:46:33 -0400
From:	Murali Karicheri <m-karicheri2@...com>
To:	<linux-kernel@...r.kernel.org>, <john.stultz@...aro.org>,
	<tglx@...utronix.de>
CC:	"Kristo, Tero" <t-kristo@...com>
Subject: Re: Export clocks_calc_mult_shift() function

On 03/14/2016 11:27 AM, Murali Karicheri wrote:
> On 03/08/2016 05:25 PM, Murali Karicheri wrote:
>> Hi,
>>
>> I found a patch posted sometime back to export the clocksource
>> function clocks_calc_mult_shift() so that it can be called by
>> drivers that are dynamically loadable. I have not seen any
>> comment against this. Wondering why this is not merged. We require
>> this function exported for use in our driver as well. Can you merge
>> the patch please. Or do you suggest me to repost the same?
>>
>> http://lkml.iu.edu/hypermail/linux/kernel/1502.2/01641.html
>>
>> Thanks
>>
> John,
> 
> Some reason, your response didn't make into my inbox. So I am 
> reproducing it below.
> 
>> Why would the clocksource driver need to calculate the hz/shift value
>> instead of using the clocksource_register_hz/khz functions?
>>
>> thanks
>> -john
> 
> John,
> 
> In this use case, the timestamp for Tx/Rx is generated by a firmware
> that attach the timestamp raw count to the packet meta data when the
> same is received from the Packet Accelerator h/w at the ingress.
> We need to convert this raw count value to nano second and use a code
> like this.
> 
> /* Convert a raw PA timer count to nanoseconds
>  */
> static inline u64 tstamp_raw_to_ns(struct pa_core_device *core_dev, u32 lo,
>                                    u32 hi)
> {
>         u32 mult = core_dev->timestamp_info.mult;
>         u32 shift = core_dev->timestamp_info.shift;
>         u64 result;
> 
>         /* Minimize overflow errors by doing this in pieces */
>         result  = ((u64)lo * mult) >> shift;
>         result += ((u64)hi << (32 - shift)) * mult;
> 
>         return result;
> }
> 
> The mult, shift values are obtained using the existing clocks_calc_mult_shift()
> that will not work, if our driver is built as a dynamically loadable module
> as the symbol is not exported. 
> 
> Is there an alternative way of doing this without exporting this function. 
> clocksource_register_hz/khz() can't help in this, right?
> 
John,

I didn't see any response? Can I send a patch to export clocks_calc_mult_shift() function??

-- 
Murali Karicheri
Linux Kernel, Keystone