Re: AM335x OMAP2 common clock external fixed-clock registration

Tero Kristo
2015-04-17T07:14:15Z

On 04/17/2015 05:00 AM, Michael Welling wrote:
> On Fri, Apr 17, 2015 at 01:23:50AM +0200, Sebastian Hesselbarth wrote:
>> On 17.04.2015 00:09, Michael Welling wrote:
>>> On Thu, Apr 16, 2015 at 10:37:19PM +0200, Sebastian Hesselbarth wrote:
>>>> On 16.04.2015 18:17, Michael Welling wrote:
>>>>> On Thu, Apr 16, 2015 at 07:32:32AM +0300, Tero Kristo wrote:
>>>>>> On 04/15/2015 11:51 PM, Michael Welling wrote:
>>>>>>> On Wed, Apr 15, 2015 at 01:45:53PM -0700, Mike Turquette wrote:
>>>>>>>> On Wed, Apr 15, 2015 at 12:47 PM, Michael Welling <mwelling@ieee.org> wrote:
>>>> [...]
>>>>>>>>> There is still an issue with the si5351.
>>>>>>>>>
>>>>>>>>> I had to comment out the clk_put here for the frequency to show up:
>>>>>>>>> http://lxr.free-electrons.com/source/drivers/clk/clk-si5351.c#L1133
>>>>>>>>>
>>>>>>>>> Ideas?
>>>>>>>>
>>>>>>>> What is the most recent upstream commit that you are based on?
>>>>>>>
>>>>>>> I am working from 4.0.0-rc7.
>>>>>>>
>>>>>>> 7b43b47373d40d557cd7e1a84a0bd8ebc4d745ab
>>>>>>
>>>>>> Hmm, I wonder why si5351 calls clk_put immediately after of_clk_get
>>>>>> in the first place, as far as I understand this destroys the clock
>>>>>> handle, which is still being used later in the code.
>>>>>
>>>>> Not sure how this ever worked. This has been in the code since the
>>>>> initial commit.
>>>>
>>>> The reason it worked before may be related with recent rework of
>>>> clk_put() itself and clk cookies instead of pointers. I lost track on
>>>> the recent clk subsystem changes here, sorry.
>>>>
>>>> However, droping the clk immediately surely isn't right.
>>>> The thing is, we can remove the clk_put() just because there is no
>>>> _remove() for that driver. I remember that back in the days the driver
>>>> was mainlined, clk removal wasn't too easy.
>>>>
>>>> FWIW, as soon as _remove() support will be added by someone, we'll have
>>>> to rethink passing struct clk* by platform_data or at least
>>>> double-check if we ever used [of_]clk_get() to obtain it.
>>>>
>>>> Mind to send a patch removing the clk_put() on !IS_ERR and add a proper
>>>> error path instead? While of_clk_get() is the only calls that need
>>>> cleanup on error in si5351_dt_parse() we should probably move that
>>>> calls to the end of this function. Otherwise we'd also have to cleanup
>>>> on every of_parse_foo() failure.
>>>
>>> What would be the proper error path?
>>> What cleanup is required?
>>
>> A proper error path would be to release any claimed resource
>> on any error. If you look at the code, the only resources that
>> need to be released are the two clocks in question.
>
> So for every error return in the probe function and in the of si5351_dt_parse
> it needs to clk_put first right?
>
> See attached patch to see if we are on the same page.
>
>>
>>> It should be noted that there are more deep rooted issues with the driver
>>> that I have noticed. For one the driver behaves differently if the debugging
>>> is on and when it is off.
>>
>> I guess you mean #define DEBUG in the driver?
>
> Yes.
>
>>
>>> Here is what the kernel reports with debugging off:
>>
>> Do you have any measurement equipment to check what is actually set?
>
> Yes, I have an oscilloscope here at my desk.
> The reported numbers do not always correspond to the actual output in some
> cases.
>
> The ms2 output has appeared to stop working all together sometime whilest
> testing. I may have to solder a new chip on there.
>
> Could misconfiguration damage the chip?
>
>>
>>> root@som3517-som200:~# cat /sys/kernel/debug/clk/clk_summary
>>> clock enable_cnt prepare_cnt rate accuracy phase
>>> ----------------------------------------------------------------------------------------
>>> ref27 0 0 27000000 0 0
>>> xtal 0 0 27000000 0 0
>>> pllb 0 0 599999994 0 0
>>> ms0 0 0 12499999 0 0
>>> clk0 0 0 12499999 0 0
>>> plla 0 0 599999994 0 0
>>> ms2 0 0 8219178 0 0
>>> clk2 0 0 8219178 0 0
>>> ms1 0 0 94117646 0 0
>>> clk1 0 0 94117646 0 0
>>>
>>> Here is what the kernel reports with debugging on:
>>> clock enable_cnt prepare_cnt rate accuracy phase
>>> ----------------------------------------------------------------------------------------
>>> ref27 0 0 27000000 0 0
>>> xtal 0 0 27000000 0 0
>>> pllb 0 0 884736000 0 0
>>> ms0 0 0 18432000 0 0
>>> clk0 0 0 18432000 0 0
>>
>> Is this what you expect for clk0?
>
> Yes.
>
>>
>>> plla 0 0 897023997 0 0
>>> ms2 0 0 12287999 0 0
>>> clk2 0 0 12287999 0 0
>>
>> ditto for clk2?
>
> Yes.
>
>>
>>> ms1 0 0 140709646 0 0
>>> clk1 0 0 140709646 0 0
>>
>> This is wrong, I agree. Looks like round_rate()/recalc_rate() of msynth
>> or clkout is broken with respect to non-pll-master clocks.
>>
>> I had a quick look at drivers/clk.c too, there has been a lot of churn
>> in clk API since I last booted my device using si5351.
>>
>> Is there any way to try out a less recent kernel, let's say two or
>> three releases before 4.0?
>
> Could you provide a specific version that you think has the best chances of
> working?
>
>>
>> We should just confirm that there has been an issue with it before
>> already.
>>
>> I have no clue about the debug on/off issue at the moment.
>>
>>> Note this is with the following devicetree entry:
>>> si5351: clock-generator {
>>> #address-cells = <1>;
>>> #size-cells = <0>;
>>> #clock-cells = <1>;
>>> compatible = "silabs,si5351a-msop";
>>> reg = <0x60>;
>>> status = "okay";
>>>
>>> /* connect xtal input to 27MHz reference */
>>> clocks = <&ref27>;
>>>
>>> /* connect xtal input as source of pll0 and pll1 */
>>> silabs,pll-source = <0 0>, <1 0>;
>>>
>>> clkout0: clkout0 {
>>> reg = <0>;
>>> silabs,drive-strength = <8>;
>>> silabs,multisynth-source = <1>;
>>> silabs,clock-source = <0>;
>>> silabs,pll-master;
>>> clock-frequency = <18432000>;
>>> };
>>>
>>> clkout1: clkout1 {
>>> reg = <1>;
>>> silabs,drive-strength = <8>;
>>> silabs,multisynth-source = <0>;
>>> silabs,clock-source = <0>;
>>> clock-frequency = <8000000>;
>>> };
>>>
>>> clkout2: clkout2 {
>>> reg = <2>;
>>> silabs,drive-strength = <8>;
>>> silabs,multisynth-source = <0>;
>>> silabs,clock-source = <0>;
>>> silabs,pll-master;
>>> clock-frequency = <12288000>;
>>> };
>>> };
>>>
>>> I am losing hope that this driver is stable enough to even use in production.
>>
>> Who said it is stable for production use? The driver is written from
>> scratch based on _very_ limited information of the datasheet an appnote.
>> Also, I only have a single setup with si5351, that is no way enough to
>> test every combination.
>
> Well it is not in staging and I am sure it took much work to get it working
> for you.

non-staging doesn't mean code is absolutely bug free. Linux kernel is
still just software, and as we know, every piece of software has bugs
(except maybe the simplest hello-world app.)

>>
>> I never heard serious complaints before, so either you help improving
>> this driver or better ask SiLabs for a table-based driver for your
>> specific setup.
>
> I have routines to program the chip from U-Boot and Linux userspace using
> the table method. I was hoping that a mainline driver could replace these
> hackish utilities.

You can still replace your hack solution.

The beauty of linux comes in that if you find a bug someplace, you can
just fix it, post a patch upstream, and get it fixed for good. :)

-Tero