linux-kernel - Re: [PATCH] clk: scpi: error when clock fails to register

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Message-ID: <76efd418-9fd5-6ac5-b4c9-c75c5df69df0@arm.com>
Date:   Wed, 28 Jun 2017 16:52:36 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Jerome Brunet <jbrunet@...libre.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Neil Armstrong <narmstrong@...libre.com>,
        Kevin Hilman <khilman@...libre.com>
Subject: Re: [PATCH] clk: scpi: error when clock fails to register



On 28/06/17 16:38, Jerome Brunet wrote:
> On Wed, 2017-06-28 at 16:04 +0100, Sudeep Holla wrote:
>>
>> On 28/06/17 14:53, Jerome Brunet wrote:
>>> Current implementation of scpi_clk_add just print a warning when clock
>>> fails to register but then keep going as if nothing happened. The
>>> provider is then registered with bogus data.
>>>
>>> This may latter lead to an Oops in __clk_create_clk when
>>> hlist_add_head(&clk->clks_node, &hw->core->clks) is called.
>>>
>> What's the path of this call ? I see one in devm_clk_hw_register
>> but that's one which failed.
>>
> 
> bL cpu freq driver requesting the cpu clock, which failed to register. Here the
> Oops call trace:
> 
> [    2.202284] [<ffff00000849a058>] __clk_create_clk.part.18+0x68/0xb0
> [    2.208494] [<ffff00000849ac2c>] __of_clk_get_from_provider+0xfc/0x140
> [    2.214962] [<ffff000008496c28>] __of_clk_get_by_name+0x100/0x118
> [    2.220999] [<ffff000008496c94>] clk_get+0x2c/0x78
> [    2.225744] [<ffff000008570110>] dev_pm_opp_get_opp_table+0xb0/0x118
> [    2.232039] [<ffff000008570940>] dev_pm_opp_add+0x20/0x68
> [    2.237388] [<ffff0000087a0f30>] scpi_init_opp_table+0xa8/0x188
> [    2.243252] [<ffff0000087a0558>] _get_cluster_clk_and_freq_table+0x80/0x180
> [    2.250151] [<ffff0000087a0a48>] bL_cpufreq_init+0x3f0/0x480
> [    2.255758] [<ffff00000879eed8>] cpufreq_online+0xc0/0x658
> [    2.261191] [<ffff00000879f500>] cpufreq_add_dev+0x78/0x88
> [    2.266625] [<ffff00000855c2c4>] subsys_interface_register+0x84/0xc8
> [    2.272922] [<ffff00000879e330>] cpufreq_register_driver+0x138/0x1b8
> [    2.279218] [<ffff0000087a0b4c>] bL_cpufreq_register+0x74/0x120
> [    2.285083] [<ffff0000087a1038>] scpi_cpufreq_probe+0x28/0x38
> [    2.290776] [<ffff00000855fbf0>] platform_drv_probe+0x50/0xb8
> [    2.296468] [<ffff00000855dd84>] driver_probe_device+0x21c/0x2d8
> 

Thanks for this stack. I just worked out the same path now. I did come
up with the patch as below. That should work if my understanding is correct.

> But that's not the point. The point is there is path in clk-scpi driver which
> registers uninitialized data in the clock provider. That's not good. 
> 
>> Also one of the reason for keeping it continuing is, if firmware fails
>> on some non-critical clock, that's fine rather than punishing the entire
>> set of clocks and may even fail the boot.
> 
> I understand, but you have no way to know whether a clock is critical or not so 
> this explanation looks a bit weak, plus it does not keep the boot from failing
> ... not for me at least.
> 
> As explained this approach is registering corrupt data in the provider when
> failing. It makes the kernel Oops, it shall be fixed.
> 

Agreed, I want to look at ways to fix that, hence requested you more data.

> If you have a better solution later on, I don't think there would be any problem
> to revert this patch.
> 

Sure I am not against the patch as a fix. I was just trying to better
understand the problem. I had seen the usefulness of skipping on Juno
platforms
in earlier days. Also I am now working on the new SCMI[1] specification
and just want to cover this.

---

diff --git i/drivers/clk/clk-scpi.c w/drivers/clk/clk-scpi.c
index 96d37175d0ad..d83c0b84798d 100644
--- i/drivers/clk/clk-scpi.c
+++ w/drivers/clk/clk-scpi.c
@@ -245,11 +245,14 @@ static int scpi_clk_add(struct device *dev, struct
device_node *np,
                sclk->id = val;

                err = scpi_clk_ops_init(dev, match, sclk, name);
-               if (err)
+               if (err) {
                        dev_err(dev, "failed to register clock '%s'\n",
name);
-               else
+                       clk_data->clk[idx] = NULL;
+                       devm_kfree(dev, sclk);
+               } else {
                        dev_dbg(dev, "Registered clock '%s'\n", name);
-               clk_data->clk[idx] = sclk;
+                       clk_data->clk[idx] = sclk;
+               }
        }

        return of_clk_add_hw_provider(np, scpi_of_clk_src_get, clk_data);

-- 
Regards,
Sudeep