[PATCH 04/10] timer: cadence-ttc: Add timer_early functions

[Michal Simek]

Hi Stefan,

On 9/30/22 15:45, Stefan Roese wrote:
> Hi Michal,
> 
> On 30.09.22 14:02, Michal Simek wrote:
>> Hi Simon and Stefan,
>>
>> On 9/28/22 03:54, Simon Glass wrote:
>>>> Hi Simon,
>>>> Hi Michal,
>>>>
>>>> On 25.09.22 16:15, Simon Glass wrote:
>>>>> Hi Stefan,
>>>>>
>>>>> On Wed, 21 Sept 2022 at 08:06, Stefan Roese <sr at denx.de> wrote:
>>>>>>
>>>>>> Currently this timer driver provides timer_get_boot_us() to support the
>>>>>> BOOTSTAGE functionality. This patch adds the timer_early functions so
>>>>>> that the "normal" timer functions can be used, when CONFIG_TIMER_EARLY
>>>>>> is enabled.
>>>>>>
>>>>>> timer_get_boot_us() will get removed in a follow-up patch, once the
>>>>>> BOOTSTAGE interface is migrated to timer_get_us().
>>>>>>
>>>>>> Signed-off-by: Stefan Roese <sr at denx.de>
>>>>>> Cc: Michal Simek <michal.simek at xilinx.com>
>>>>>> ---
>>>>>>    drivers/timer/cadence-ttc.c | 25 +++++++++++++++++++++++++
>>>>>>    1 file changed, 25 insertions(+)
>>>>>>
>>>>>> diff --git a/drivers/timer/cadence-ttc.c b/drivers/timer/cadence-ttc.c
>>>>>> index 2eff45060ad6..e26c7923a140 100644
>>>>>> --- a/drivers/timer/cadence-ttc.c
>>>>>> +++ b/drivers/timer/cadence-ttc.c
>>>>>> @@ -58,6 +58,31 @@ ulong timer_get_boot_us(void)
>>>>>>    }
>>>>>>    #endif
>>>>>>
>>>>>> +unsigned long notrace timer_early_get_rate(void)
>>>>>> +{
>>>>>> +       return 1;
>>>>>> +}
>>>>>> +
>>>>>> +u64 notrace timer_early_get_count(void)
>>>>>> +{
>>>>>> +       u64 ticks = 0;
>>>>>> +       u32 rate = 1;
>>>>>> +       u64 us;
>>>>>> +       int ret;
>>>>>> +
>>>>>> +       ret = dm_timer_init();
>>>>>
>>>>> I don't think you can call this if you want to support bootstage,
>>>>> since driver model may not be inited.
>>>>
>>>> Yes, thanks for noticing. Still, this code is copied from the original
>>>> timer_get_boot_us() function in this driver. Which also has problems
>>>> with early timer access AFAICT.
>>>
>>> Yes, good point.
>>>
>>> Reviewed-by: Simon Glass <sjg at chromium.org>
>>
>> I looked at it and kind of interesting code. For getting this working with 
>> this whole series if ttc gets u-boot,dm-pre-reloc everthing is working fine.
> 
> Yes, makes sense that this is needed.
> 
>> diff --git a/arch/arm/dts/zynqmp-r5.dts b/arch/arm/dts/zynqmp-r5.dts
>> index a72172ef2ea4..8059931f2162 100644
>> --- a/arch/arm/dts/zynqmp-r5.dts
>> +++ b/arch/arm/dts/zynqmp-r5.dts
>> @@ -56,6 +56,7 @@
>>
>>                  ttc0: timer at ff110000 {
>>                          compatible = "cdns,ttc";
>> +                       u-boot,dm-pre-reloc;
>>                          status = "okay";
>>                          reg = <0xff110000 0x1000>;
>>                          timer-width = <32>;
>>
>> What I see based on behavior. Every bootstage call is asking for 
>> timer_early_get_count() and because dm_timer_init() is failing 0 is returned.
>>
>> Inside initf_dm() dm_init_and_scan() is called and initialized timer uclass 
>> also with timer instance. With u-boot,dm-pre-reloc also cadence timer driver.
>> On the next dm_timer_init() gd->timer is initialized and value is returned and 
>> initf_dm() passes.
> 
> This "early" implementation of the counter is broken, as you have
> noticed above. Resulting in timer functions only returning valid
> values after dm_timer_init(). This timer driver needs re-written
> early_timer functions, that will return proper timer values even in
> the early boot phase. Please take a look at e.g. rockchip_timer.c,
> perhaps something similar works for the cadence timer driver as well?

I looked at it and there is a code when OF_REAL is enabled. If not then 0 is 
returned. That's why I can't see any difference between rockchip and cadence 
when OF_REAL is not enabled.

And not sure how this is working in rockchip case. Who is starting timer in 
their case? I see start when probe happens but after it dm_timer_init() should 
return 0 and value can be obtained.

> 
>> Here is the log and output from bootstage.
>>
>> U-Boot 2022.10-rc5-00130-g1be5bed207c9 (Sep 30 2022 - 14:00:08 +0200)
>>
>> Model: Xilinx ZynqMP R5
>> DRAM:  512 MiB
>> Core:  7 devices, 7 uclasses, devicetree: embed
>> MMC:
>> Loading Environment from nowhere... OK
>> In:    serial at ff010000
>> Out:   serial at ff010000
>> Err:   serial at ff010000
>> Net:   No ethernet found.
>> ZynqMP r5> dm tree
>>   Class     Index  Probed  Driver                Name
>> -----------------------------------------------------------
>>   root          0  [ + ]   root_driver           root_driver
>>   clk           0  [ + ]   fixed_clock           |-- clk100
>>   simple_bus    0  [ + ]   simple_bus            |-- amba
>>   timer         0  [ + ]   cadence_ttc           |   |-- timer at ff110000
>>   serial        0  [ + ]   serial_zynq           |   `-- serial at ff010000
>>   bootstd       0  [   ]   bootstd_drv           `-- bootstd
>>   bootmeth      0  [   ]   bootmeth_distro           `-- distro
>> ZynqMP r5> bootstage report
>> Timer summary in microseconds (8 records):
>>         Mark    Elapsed  Stage
>>            0          0  reset
>>            0          0  board_init_f
>>            0          0  dm_f
>>            0          0  dm_r
>>       16,319     16,319  eth_common_init
>>       18,061      1,742  main_loop
>>       18,281        220  cli_loop
>>       29,249     10,968  board_init_r
>>
>> Accumulated time:
> 
> Take a look at sandbox - here you will get proper early timing values
> as well:

I expect early functions are called before DM is ready that's why to get it work 
that early we would have to start timer on the first call of early function.
It is definitely doable but is it worth to do it?

Is there any other use case where early timer counts are needed other then 
bootstage?

Thanks,
Michal