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Re: Export clocks_calc_mult_shift() function

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  Re: Export clocks_calc_mult_shift() function Murali Karicheri <m-karicheri2@ti.com> - 2016-03-30 18:50 +0200
    Re: Export clocks_calc_mult_shift() function John Stultz <john.stultz@linaro.org> - 2016-03-30 19:10 +0200
      Re: Export clocks_calc_mult_shift() function Murali Karicheri <m-karicheri2@ti.com> - 2016-04-01 00:10 +0200
        Re: Export clocks_calc_mult_shift() function John Stultz <john.stultz@linaro.org> - 2016-04-01 01:00 +0200
    Re: Export clocks_calc_mult_shift() function John Stultz <john.stultz@linaro.org> - 2016-03-30 19:10 +0200

#1367410 — 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

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#1367468

On Wed, Mar 30, 2016 at 10:01 AM, John Stultz <john.stultz@linaro.org> wrote:
> On Wed, Mar 30, 2016 at 9:46 AM, Murali Karicheri <m-karicheri2@ti.com> wrote:
>> I didn't see any response? Can I send a patch to export clocks_calc_mult_shift() function??
>
> Sorry. I was out at a conference when you first sent this out and then
> I just now got back from vacation.
>
> I didn't realize this was for the
>

Heh. Maybe I'm not all the way back from vacation yet.

I was going to say....  I didn't realize this was for the timecounter
structures. And yes, in that case we don't have a easy helper to
calculate the mult/shift pair.

thanks
-john

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#1368853

On 03/30/2016 01:02 PM, John Stultz wrote:
> On Wed, Mar 30, 2016 at 10:01 AM, John Stultz <john.stultz@linaro.org> wrote:
>> On Wed, Mar 30, 2016 at 9:46 AM, Murali Karicheri <m-karicheri2@ti.com> wrote:
>>> I didn't see any response? Can I send a patch to export clocks_calc_mult_shift() function??
>>
>> Sorry. I was out at a conference when you first sent this out and then
>> I just now got back from vacation.
>>
>> I didn't realize this was for the
>>
> 
> Heh. Maybe I'm not all the way back from vacation yet.
> 
> I was going to say....  I didn't realize this was for the timecounter
> structures. And yes, in that case we don't have a easy helper to
> calculate the mult/shift pair.
John,

So does that mean a green signal for me to send a patch for exporting this?

Thanks

Murali
> 
> thanks
> -john
> 


-- 
Murali Karicheri
Linux Kernel, Keystone

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#1368875

On Thu, Mar 31, 2016 at 3:07 PM, Murali Karicheri <m-karicheri2@ti.com> wrote:
> On 03/30/2016 01:02 PM, John Stultz wrote:
>> On Wed, Mar 30, 2016 at 10:01 AM, John Stultz <john.stultz@linaro.org> wrote:
>>> On Wed, Mar 30, 2016 at 9:46 AM, Murali Karicheri <m-karicheri2@ti.com> wrote:
>>>> I didn't see any response? Can I send a patch to export clocks_calc_mult_shift() function??
>>>
>>> Sorry. I was out at a conference when you first sent this out and then
>>> I just now got back from vacation.
>>>
>>> I didn't realize this was for the
>>>
>>
>> Heh. Maybe I'm not all the way back from vacation yet.
>>
>> I was going to say....  I didn't realize this was for the timecounter
>> structures. And yes, in that case we don't have a easy helper to
>> calculate the mult/shift pair.
> John,
>
> So does that mean a green signal for me to send a patch for exporting this?

As I said in the previous mail, I'd prefer you export a helper
function that avoids having the driver select the interval range, and
instead picks a proper value for a given freq. But yea, I understand
we need something here.

thanks
-john

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#1367470

On Wed, Mar 30, 2016 at 9:46 AM, Murali Karicheri <m-karicheri2@ti.com> wrote:
> 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??

Sorry. I was out at a conference when you first sent this out and then
I just now got back from vacation.

I didn't realize this was for the

So I'm still hesitant to export that function because its a bit too
raw and I'm not sure drivers should be trusted to handle the inherent
tradeoffs it makes (adjustability and accuracy vs counter delta limits
to avoid mult overflow) properly without much guidance.

Could you instead export a helper function like what
clocksource_register_hz/khz() provides? So the timecounter drivers get
usable values w/o having to sort out the interval length (as it
probably would just be blindly copy-pasted in from somewhere else).

thanks
-john

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