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

[Dmitry Osipenko <digetx@gmail.com>]

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.