Export clocks_calc_mult_shift() function

Export clocks_calc_mult_shift() function

[Murali Karicheri]

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

-- 
Murali Karicheri
Linux Kernel, Keystone

Re: Export clocks_calc_mult_shift() function

[John Stultz]

On Wed, Mar 9, 2016 at 5:25 AM, Murali Karicheri <m-karicheri2@ti.com> 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?

Why would the clocksource driver need to calculate the hz/shift value
instead of using the clocksource_register_hz/khz functions?

thanks
-john

Re: Export clocks_calc_mult_shift() function

[Murali Karicheri]

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?

-- 
Murali Karicheri
Linux Kernel, Keystone

Re: Export clocks_calc_mult_shift() function

[Murali Karicheri]

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

Re: Export clocks_calc_mult_shift() function

[John Stultz]

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

Re: Export clocks_calc_mult_shift() function

[John Stultz]

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

Re: Export clocks_calc_mult_shift() function

[Murali Karicheri]

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

Re: Export clocks_calc_mult_shift() function

[John Stultz]

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