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

[Dmitry Osipenko <digetx@gmail.com>]

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@nvidia.com>
>>>> Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
>>>> ---
>>>>  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?