linux-kernel - Re: BUG: A31s Not booting anymore

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Date:   Tue, 13 Feb 2018 12:32:15 +0100
From:   Philipp Rossak <embed3d@...il.com>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     linux-sunxi <linux-sunxi@...glegroups.com>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-clk <linux-clk@...r.kernel.org>
Subject: Re: BUG: A31s Not booting anymore



On 13.02.2018 03:59, Chen-Yu Tsai wrote:
> On Tue, Feb 13, 2018 at 9:25 AM, Philipp Rossak <embed3d@...il.com> wrote:
>>
>>
>> On 12.02.2018 19:21, Philipp Rossak wrote:
>>>
>>> Hey,
>>>
>>> When I try to boot my A31s (Bananapi M2) u-boot is showing only Starting
>>> kernel ... . After enabling the earlyprintk I could capture this log: [1].
>>>
>>> After reverting those 5 commits from Chen-Yu I was able to boot again:
>>>
>>>
>>> clk: sunxi-ng: Support fixed post-dividers on NM style clocks
>>> 7d333ef1cc1b8c8951f3a2c41f6406e2295d8be9
>>>
>>> clk: sunxi-ng: sun8i: a83t: Add /2 fixed post divider to audio PLL
>>> 10e6eb4f2c5b35ae71c9bc0db83d74238719b453
>>>
>>> clk: sunxi-ng: sun8i: a83t: Use sigma-delta modulation for audio PLL
>>> e952ca3c6b2ffdfbf9618e4bd3e9aad1ff3f5eb4
>>>
>>> clk: sunxi-ng: Support fixed post-dividers on MP style clocks
>>> 946797aa3f08e2f6f5992f3ec2be44791e9b9260
>>>
>>> clk: sunxi-ng: sun50i: a64: Add 2x fixed post-divider to MMC module clocks
>>> 83fe3be4d1974f5f50c5e2039a1609f4960e8579
>>>
>>>
>>> I allready tried to fix it with making them save against zero:
>>>
>>> if (cmp->common.features & CCU_FEATURE_FIXED_POSTDIV && \
>>>           cmp->fixed_post_div with)
>>>                  rate *= cmp->fixed_post_div;
>>>
>>> But that didn't help.
>>>
>>> Any ideas?
>>>
>>> Regards,
>>> Philipp
>>>
>>> [1]: https://pastebin.com/64Fzzqvg
>>
>>
>> It took me some time, but I have now a few more infos:
>>
>> Right now the code breaks at this point here [1], with this clock [2].
>> If we have a look now at the clock config [3], we see here a table which is
>> an u8 array and also a fixed_predivs struct.
> 
> The u8 array is for mapping the parents from the index in the parents
> array to the actual register value you listed below.
> 
> How are you figuring out which clock is triggering this? Because that
> is not even the right type of clock. The backtrace you posted shows
> the error occurring in a DIV or M type clock, not the MP type you
> are pointing to.
> 
> Could you add some noisy printk calls to the sunxi_ccu_probe()
> function in drivers/clk/sunxi-ng/ccu_common.c so it's much clearer
> which clock is failing?

Thats what I basically did to find out which clock is failing. This here 
are the changes I'm doing [1]  and thats the dirty log [2]. It fails at 
clock NR 155 which is this one [3] mentioned before.

> 
> 
>>
>> If we have a look at the function call where it breaks [4], shouldn't the
>> table be a clk_div_table struct instead of an u8?
> 
> The table argument is an option. Did you go through how the sunxi-ng driver
> calls this function? As mentioned above, you are looking at the wrong thing.
> 
> Thanks
> ChenYu

I followed the failing call to this function (through the clock driver). 
As you can see I added an additional printk statement to see where it fails.

Regards,
Philipp
> 
>>
>> The a31s is the only board where we have this combination of a fixed_predivs
>> and a table.
>>
>> Philipp
>>
>>
>> Related Clock source register A31s:
>>
>> 0000: OSC24MHz/750=32KHz
>> 0001: LOSC
>> 0010: OSC24MHz
>> 0011: /
>> 0100: /
>> 0101: /
>> 0110: /
>> 0111: /
>> 1000: /
>> 1001: /
>> 1010: /
>> 1011: AXICLK/4
>> 1100: /
>> 1101: AHB1CLK/4
>> 1110: /
>> 1111: /
>>
>>
>> [1]:
>> http://lxr.bootlin.com/linux/v4.16-rc1/source/drivers/clk/clk-divider.c#L89
>>
>> [2]:
>> http://lxr.bootlin.com/linux/v4.16-rc1/source/drivers/clk/sunxi-ng/ccu-sun6i-a31.c#L1137
>>
>> [3]:
>> http://lxr.bootlin.com/linux/v4.16-rc1/source/drivers/clk/sunxi-ng/ccu-sun6i-a31.c#L749
>>
>> [4]:
>> http://lxr.bootlin.com/linux/v4.16-rc1/source/drivers/clk/clk-divider.c#L93
>>

[1]: https://pastebin.com/tvDunAWq
[2]: https://pastebin.com/SBn2VQLu
[3]: 
http://lxr.bootlin.com/linux/v4.16-rc1/source/include/dt-bindings/clock/sun6i-a31-ccu.h#L187