Re: [PATCH] clk: tegra: Mark APB clock as critical

[Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>]

On 29/11/17 15:08, Dmitry Osipenko wrote:
> On 29.11.2017 13:12, Jon Hunter wrote:
>>
>> On 29/11/17 00:09, Dmitry Osipenko wrote:
>>> On 29.11.2017 02:30, Dmitry Osipenko wrote:
>>>> On 23.10.2017 14:12, Jon Hunter wrote:
>>>>> Commit a140614373ae ("clk: tegra: Correct parent of the APBDMA clock")
>>>>> fixed the parent clock for APBDMA, but the consequence of this that
>>>>> after probing the APBDMA device, the APB Clock (or PCLK) is now
>>>>> disabled. Disabling the APB clock causes accesses to any other device
>>>>> on the APB to hang and prevent Tegra from booting.
>>>>>
>>>>> Currently, the APB clock is registered with the flag "CLK_IGNORE_UNUSED"
>>>>> to prevent the clock being disabled if unused on boot. However, even
>>>>> if it is used, it still needs to be always kept enabled and so update
>>>>> the flag for the APB clock to be "CLK_IS_CRITICAL".
>>>>>
>>>>> Fixes: a140614373ae ("clk: tegra: Correct parent of the APBDMA clock")
>>>>>
>>>>> Suggested-by: Peter De Schrijver <pdeschrijver-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
>>>>> Signed-off-by: Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
>>>>> ---
>>>>>  drivers/clk/tegra/clk-tegra-super-gen4.c | 2 +-
>>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/clk/tegra/clk-tegra-super-gen4.c b/drivers/clk/tegra/clk-tegra-super-gen4.c
>>>>> index 4f6fd307cb70..10047107c1dc 100644
>>>>> --- a/drivers/clk/tegra/clk-tegra-super-gen4.c
>>>>> +++ b/drivers/clk/tegra/clk-tegra-super-gen4.c
>>>>> @@ -166,7 +166,7 @@ static void __init tegra_sclk_init(void __iomem *clk_base,
>>>>>  				   clk_base + SYSTEM_CLK_RATE, 0, 2, 0,
>>>>>  				   &sysrate_lock);
>>>>>  	clk = clk_register_gate(NULL, "pclk", "pclk_div", CLK_SET_RATE_PARENT |
>>>>> -				CLK_IGNORE_UNUSED, clk_base + SYSTEM_CLK_RATE,
>>>>> +				CLK_IS_CRITICAL, clk_base + SYSTEM_CLK_RATE,
>>>>>  				3, CLK_GATE_SET_TO_DISABLE, &sysrate_lock);
>>>>>  	*dt_clk = clk;
>>>>>  }
>>>>>
>>>>
>>>> Unfortunately this patch somehow breaks Tegra20, getting a hang during boot. For
>>>> now I don't know what's the cause of the issue, may take a more detailed look
>>>> soon. If you have any suggestions, please tell.
>>>>
>>>
>>> It looks like that with CLK_IS_CRITICAL flag, pclk is getting enabled before
>>> clock rate is setup and in result it is enabled with some invalid rate config.
>>
>> What Tegra20 platform? I have not seen any issues with booting Tegra20
>> trimslice with v4.15-rc1 or next-20171129. I am surprised this clock
>> would not have been enabled by the bootloader and hence rate set correctly.
>>
> 
> It is not an upstream'ed device and it uses proprietary bootloader. But turned
> out it is unrelated.. the actual problem is that with the offending patch
> applied, for some reason PLL_M is now getting disabled on SCLK reparent, PLL_M
> is a critical clock that feeds EMC and marking it as CLK_IS_CRITICAL fixes issue
> for me.
> 
> Jon, could you please try to revert "Mark APB clock as critical" patch, mark the
> PLL_M as critical and re-test?

Sorry but you have lost me here. I am not sure I understand the relation
between the problem you are describing and this change.

Please note that the problem I was fixing with this patch was seen on
Tegra114/124 and not Tegra20. I don't recall seeing any issues with
Tegra20 and I just checked Tegra20 is still booting for me even when
reverting this. So it sounds like a different problem AFAICT.

Cheers
Jon

-- 
nvpublic