[PATCH v4 1/5] clk: sunxi-ng: common: Support minimum and maximum rate

[Pafford, Robert J.]

Frank Oltmanns <frank at oltmanns.dev> writes:

> Hi Robert,
>
> 26.06.2024 18:03:24 Pafford, Robert J. <pafford.9 at buckeyemail.osu.edu>:
>
>> Hi Frank,
>>
>> Moving to a new for loop makes sense. Let me know when you have a patch
>
> The patch is here, strange you didn't receive it:
> https://lore.kernel.org/all/20240623-sunxi-ng_fix_common_probe-v1-1-7c97e32824a1@oltmanns.dev/

Ah, this must have slipped through my inbox. I just applied it on my board and it is
now cooperating with the min/max clock rates!

>
>> and I'll be glad to test it on my board. I do also wonder if this may
>> have contributed to some of the HDMI issues seen in the other thread.
>
> My thought's exactly!
>
> Best regards,
>   Frank
>
>>
>> Best,
>> Robert
>>
>>> Hi Robert,
>>>
>>> I'm truly sorry for the trouble the patch has caused you and for my late
>>> reply!
>>>
>>> On 2024-06-14 at 23:52:08 +0000, "Pafford, Robert J." <pafford.9 at buckeyemail.osu.edu> wrote:
>>>>> The Allwinner SoC's typically have an upper and lower limit for their
>>>>> clocks' rates. Up until now, support for that has been implemented
>>>>> separately for each clock type.
>>>>>
>>>>> Implement that functionality in the sunxi-ng's common part making use of
>>>>> the CCF rate liming capabilities, so that it is available for all clock
>>>>> types.
>>>>>
>>>>> Suggested-by: Maxime Ripard <mripard at kernel.org>
>>>>> Signed-off-by: Frank Oltmanns <frank at oltmanns.dev>
>>>>> Cc: stable at vger.kernel.org
>>>>> ---
>>>>>   drivers/clk/sunxi-ng/ccu_common.c | 19 +++++++++++++++++++
>>>>>   drivers/clk/sunxi-ng/ccu_common.h |  3 +++
>>>>>   2 files changed, 22 insertions(+)
>>>>
>>>> This patch appears to cause a buffer under-read bug due to the call to 'hw_to_ccu_common', which assumes all entries
>>>> in the desc->hw_clocks->hws array are contained in ccu_common structs.
>>>>
>>>> However, not all clocks in the array are contained in ccu_common structs. For example, as part
>>>> of the "sun20i-d1-ccu" driver, the "pll-video0" clock holds the 'clk_hw' struct inside of a 'clk_fixed_factor' struct,
>>>> as it is a fixed factor clock based on the "pll-video0-4x" clock, created with the CLK_FIXED_FACTOR_HWS macro.
>>>> This results in undefined behavior as the hw_to_ccu_common returns an invalid pointer referencing memory before the
>>>> 'clk_fixed_factor' struct.
>>>>
>>>
>>> Great catch! At first glance, it seems to me that calling
>>> clk_hw_set_rate_range() in sunxi_ccu_probe() should not have happenend
>>> in the loop that iterates over the hw_clks.
>>>
>>> Instead we should add one more loop that iterates over the ccu_clks.
>>> Note, that there is already one such loop but, unfortunately, we can't
>>> use that as it happens before the hw_clks loop and we can only call
>>> clk_hw_set_rate_range() after the hw_clk has been registered.
>>>
>>> Hence, I propose to move the offending code to a new loop:
>>>         for (i = 0; i < desc->num_ccu_clks; i++) {
>>>                 struct ccu_common *cclk = desc->ccu_clks[i];
>>>
>>>                 if (!cclk)
>>>                         continue;
>>>
>>>                 if (cclk->max_rate)
>>>                         clk_hw_set_rate_range(&cclk->hw, common->min_rate,
>>>                                               common->max_rate);
>>>                 else
>>>                         WARN(cclk->min_rate,
>>>                              "No max_rate, ignoring min_rate of clock %d - %s\n",
>>>                              i, cclk->hw.init->name);
>>>         }
>>>
>>> I haven't tested (or even compiled) the above, but I'll test and send a
>>> patch within the next few days for you to test.
>>>
>>> Thanks again,
>>>   Frank
>>>
>>>>
>>>> I have attached kernel warnings from a system based on the "sun8i-t113s.dtsi" device tree, where the memory contains
>>>> a non-zero value for the min-rate but a zero value for the max-rate, triggering the "No max_rate, ignoring min_rate"
>>>> warning in the 'sunxi_ccu_probe' function.
>>>>
>>>> [...]

Thanks,
Robert