Re: [PATCH V2 3/8] soc: qcom-geni-se: Add interconnect support to fix earlycon crash

[Akash Asthana <akashast-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>]

Hi Evan

On 3/18/2020 12:38 AM, Evan Green wrote:
> On Tue, Mar 17, 2020 at 3:58 AM Akash Asthana <akashast-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org> wrote:
>> Hi Matthias,
>>
>> On 3/14/2020 2:14 AM, Matthias Kaehlcke wrote:
>>> Hi Akash,
>>>
>>> On Fri, Mar 13, 2020 at 06:42:09PM +0530, Akash Asthana wrote:
>>>> V1 patch@https://patchwork.kernel.org/patch/11386469/ caused SC7180 system
>>>> to reset at boot time.
>>> The v1 patch isn't relevant in the commit message, please just describe the
>>> problem. Also the crash only occurs when earlycon is used.
>> ok
>>>> As QUP core clock is shared among all the SE drivers present on particular
>>>> QUP wrapper, the reset seen is due to earlycon usage after QUP core clock
>>>> is put to 0 from other SE drivers before real console comes up.
>>>>
>>>> As earlycon can't vote for it's QUP core need, to fix this add ICC
>>>> support to common/QUP wrapper driver and put vote for QUP core from
>>>> probe on behalf of earlycon and remove vote during sys suspend.
>>> Only removing the vote on suspend isn't ideal, the system might never get
>>> suspended. That said I don't have a really good alternative suggestion.
>>>
>>> One thing you could possibly do is to launch a delayed work, check
>>> console_device() every second or so and remove the vote when it returns
>>> non-NULL. Not claiming this would be a great solution ...
>>>
>>> The cleanest solution might be a notifier when the early console is
>>> unregistered, it seems somewhat over-engineered though ... Then again
>>> other (future) uart drivers with interconnect support might run into
>>> the same problem.
>> We are hitting this problem because QUP core clocks are shared among all
>> the SE driver present in particular QUP wrapper, if other HW controllers
>> has similar architecture we will hit this issue.
>>
>> How about if we expose an API from common driver(geni-se) for putting
>> QUP core BW vote to 0.
>>
>> We call this from console probe just after uart_add_one_port call
>> (console resources are enabled as part of this call) to put core quota
>> to 0 on behalf of earlyconsole?
> +Georgi
>
> Hm, these boot proxy votes are annoying, since the whole house of
> cards comes down if you replace these votes in the wrong order.
>
> I believe consensus in the other patches was to consolidate most of
> the interconnect support into the common SE code, right?

I think what Matthias suggested is to maintain ICC functions defined 
across I2C, SPI and UART as a library in common SE code.

Still every SE driver will interact with ICC framework individually 
rather than using common SE driver as a bridge.

>   Would that
> help you with these boot proxy votes? What I'm thinking is something
> along the lines of:
>   * SPI, I2C, UART all call into the new common geni_se_icc_on/off()
> (or whatever it's called)
>   * If geni_se_icc_off() sees that console UART hasn't voted yet, save
> the votes but don't actually call icc_set(0) now.
>   * Once uart votes for the first time, call icc_set() on all of SPI,
> I2C, UART to get things back in sync.

IIUC, you are suggesting to enhancing ICC 
design@https://patchwork.kernel.org/patch/10774897/ [The very first ICC 
patch posted during sdm845 timeframe].

Where common SE driver aggregate real time BW requirement from all the 
SE driver and put net request to ICC framework.

We received comments on that version of ICC to move voting to individual 
SE driver from common driver. Hence we updated the design accordingly.

Thanks for reviewing

regards,

Akash

> That's a sort of roll-your-own solution for GENI, but we do have this
> problem elsewhere as well. A more general solution would be to have
> the interconnect providers prop things up (ie ignore votes to lower
> bandwidth) until some "go" moment where we feel we've enumerated all
> devices. I was originally thinking to model this off of something like
> clk_disable_unused(), but after chatting with Stephen it's clear
> late_initcall's aren't really indicative of all devices having
> actually come up. So I'm not sure where the appropriate "go" moment
> is.
>
> -Evan
>
>
>>>> Signed-off-by: Akash Asthana <akashast-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>
>>>> Reported-by: Matthias Kaehlcke <mka-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
>>>> ---
>>>>    drivers/soc/qcom/qcom-geni-se.c | 41 +++++++++++++++++++++++++++++++++++++++++
>>>>    1 file changed, 41 insertions(+)
>>>>
>>>> diff --git a/drivers/soc/qcom/qcom-geni-se.c b/drivers/soc/qcom/qcom-geni-se.c
>>>> index 7d622ea..d244dfc 100644
>>>> --- a/drivers/soc/qcom/qcom-geni-se.c
>>>> +++ b/drivers/soc/qcom/qcom-geni-se.c
>>>> @@ -90,6 +90,7 @@ struct geni_wrapper {
>>>>       struct device *dev;
>>>>       void __iomem *base;
>>>>       struct clk_bulk_data ahb_clks[NUM_AHB_CLKS];
>>>> +    struct icc_path *icc_path_geni_to_core;
>>>>    };
>>>>
>>>>    #define QUP_HW_VER_REG                     0x4
>>>> @@ -747,11 +748,50 @@ static int geni_se_probe(struct platform_device *pdev)
>>>>               }
>>>>       }
>>>>
>>>> +#ifdef CONFIG_SERIAL_EARLYCON
>>>> +    wrapper->icc_path_geni_to_core = devm_of_icc_get(dev, "qup-core");
>>>> +    if (IS_ERR(wrapper->icc_path_geni_to_core))
>>>> +            return PTR_ERR(wrapper->icc_path_geni_to_core);
>>>> +    /*
>>>> +     * Put minmal BW request on core clocks on behalf of early console.
>>>> +     * The vote will be removed in suspend call.
>>>> +     */
>>>> +    ret = icc_set_bw(wrapper->icc_path_geni_to_core, Bps_to_icc(1000),
>>>> +                    Bps_to_icc(1000));
>>>> +    if (ret) {
>>>> +            dev_err(&pdev->dev, "%s: ICC BW voting failed for core\n",
>>>> +                    __func__);
>>>> +            return ret;
>>>> +    }
>>> What is ugly about this is that it's done for every QUP, not only the one
>>> with the early console. Again, I don't have a good solution for it, maybe
>>> it's a limitation we have to live with :(
>> There is one more limitation from QUP core side. Core clocks for both
>> the QUP wrapper runs at same speed.
>>
>> core2x_1 = core2x_2 = max(core2x_1, core2x_2);
>>
>> So with above limitation and if we are removing early con vote from Core
>> when real console comes up. It doesn't matter whether it's done for
>> every QUP or the only with early console.
>>
>>>> +#endif
>>>> +
>>>>       dev_set_drvdata(dev, wrapper);
>>>>       dev_dbg(dev, "GENI SE Driver probed\n");
>>>>       return devm_of_platform_populate(dev);
>>>>    }
>>>>
>>>> +static int __maybe_unused geni_se_sys_suspend(struct device *dev)
>>>> +{
>>>> +    struct geni_wrapper *wrapper = dev_get_drvdata(dev);
>>>> +    int ret;
>>>> +
>>>> +#ifdef CONFIG_SERIAL_EARLYCON
>>>> +    ret = icc_set_bw(wrapper->icc_path_geni_to_core, 0, 0);
>>> I think you only want to do this on the first suspend.
>> Ok, I can add that logic using global variable.
>>> Do we need to handle the case where no 'real' console is configured?
>>> In this case the early console would be active forever and setting
>>> the bandwidths to 0 might cause a similar crash than the one you are
>>> trying to fix. Not sure if that's a real world use case, but wanted to
>>> mention it. Maybe this is an argument of the notifier approach?
>> We can't support earlycon without real console.
>>
>> As earlyconsole doesn't do any kind of resource enablement(SE clocks,
>> pinctrl, etc) it assumes that resources are already enabled from
>> previous stages.
>>
>> So if real console doesn't come up no one will vote for that SE clock,
>> and it will be disabled from clk late_init call which will result into
>> un-clocked access.
>>
>>
>>>> +    if (ret) {
>>>> +            dev_err(dev, "%s: ICC BW remove failed for core\n",
>>>> +                    __func__);
>>>> +            return ret;
>>> Aborting suspend seems too harsh since the QUP should still be fully
>>> functional unless there is a general problem with the interconnects.
>>>
>>> I would suggest to change the log to dev_warn() and return 0.
>> Ok
>>
>> Thanks for reviewing the patch.
>>
>> regards,
>>
>> Akash
>>
>> --
>> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,\na Linux Foundation Collaborative Project

-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,\na Linux Foundation Collaborative Project