On 4/30/2018 3:40 PM, Doug Anderson wrote:
> Hi,
>
> On Tue, Apr 10, 2018 at 11:34 AM, Karthik Ramasubramanian
> <kramasub@xxxxxxxxxxxxxx> wrote:
>> Hi Bjorn,
>>
>> Thanks for pulling it into your tree and helping with the verification.
>>
>> On 4/9/2018 5:46 PM, Bjorn Andersson wrote:
>>> On Mon 09 Apr 12:38 PDT 2018, Karthikeyan Ramasubramanian wrote:
>>>
>>>> Add early console support in Qualcomm Technologies Inc., GENI based
>>>> UART controller.
>>>>
>>>
>>> Hi Karthikeyan,
>>>
>>> I pulled this into my SDM845 tree and added "earlycon" to my command
>>> line, the result is a working console up until the serial driver is
>>> probed at which point the console stops.
>>>
>>>
>>> I'm expecting that this should hand over to the normal console as it is
>>> probed, unless I specify keep_bootcon in which case I expect all log
>>> entries to be printed both through the earlycon and the normal console
>>> (i.e. show up twice on the uart).
>> I suspect the issue is something to do with clocks. I will look into it
>> further and fix in the next submission.
>>
>> This is my current hypothesis: When the driver gets probed, it registers
>> the uart port which in turn invokes the console setup. The console setup
>> enables the "se" clock (geni_resources_on()->clk_prepare_enable()).
>> Enabling the "se" clock is disturbing the rate that the clock is already
>> on. Early console write is simultaneously going on while the console is
>> being set up and this clock disturbance is causing the halt.
>
> Or it could be a simple bug in this code. Specifically, your "custom
> implementation instead of readl_poll_atomic" is wrong. You don't
> ensure that "timeout_us" is evenly divisible by 10, yet you do:
>
> while (timeout_us) {
> ...;
> udelay(10);
> timeout_us -= 10;
> }
>
> One way to fix this is with this before the loop:
>
> timeout_us = DIV_ROUND_UP(timeout_us, 10) * 10;
>
>
> BTW: are you planning to spin this patch series anytime soon?
Thats a good catch. I will fix that. Let us see if it fixes the issue
that Bjorn has reported.
I will address all the comments and upload the next spin in couple of days.
>
>
> -Doug
>
Regards,
Karthik.
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