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Subject: Re: [PATCH] iommu/arm: Cleanup resources in case of probe error path
To:     Will Deacon <will@kernel.org>,
        Marek Szyprowski <m.szyprowski@samsung.com>
Cc:     Jean-Philippe Brucker <jean-philippe@linaro.org>,
        linux-arm-msm@vger.kernel.org, iommu@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org,
        Amey Narkhede <ameynarkhede03@gmail.com>,
        Jon Hunter <jonathanh@nvidia.com>,
        linux-arm-kernel@lists.infradead.org
References: <20210608164559.204023-1-ameynarkhede03@gmail.com>
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 <20210630125940.GA8515@willie-the-truck>
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 <20210701090112.GA9489@willie-the-truck>
From:   Robin Murphy <robin.murphy@arm.com>
Message-ID: <bf8d3101-1db7-ee5a-377c-2196e3ce84e3@arm.com>
Date:   Thu, 1 Jul 2021 10:11:02 +0100
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On 2021-07-01 10:01, Will Deacon wrote:
> On Thu, Jul 01, 2021 at 10:29:29AM +0200, Marek Szyprowski wrote:
>> Hi Robin,
>>
>> On 30.06.2021 16:01, Robin Murphy wrote:
>>> On 2021-06-30 14:48, Marek Szyprowski wrote:
>>>> On 30.06.2021 14:59, Will Deacon wrote:
>>>>> On Wed, Jun 30, 2021 at 02:48:15PM +0200, Marek Szyprowski wrote:
>>>>>> On 08.06.2021 18:45, Amey Narkhede wrote:
>>>>>>> If device registration fails, remove sysfs attribute
>>>>>>> and if setting bus callbacks fails, unregister the device
>>>>>>> and cleanup the sysfs attribute.
>>>>>>>
>>>>>>> Signed-off-by: Amey Narkhede <ameynarkhede03@gmail.com>
>>>>>> This patch landed in linux-next some time ago as commit 249c9dc6aa0d
>>>>>> ("iommu/arm: Cleanup resources in case of probe error path"). After
>>>>>> bisecting and some manual searching I finally found that it is
>>>>>> responsible for breaking s2idle on DragonBoard 410c. Here is the log
>>>>>> (captured with no_console_suspend):
>>>>>>
>>>>>> # time rtcwake -s10 -mmem
>>>>>> rtcwake: wakeup from "mem" using /dev/rtc0 at Thu Janï¿½ 1 00:02:13 1970
>>>>>> PM: suspend entry (s2idle)
>>>>>> Filesystems sync: 0.002 seconds
>>>>>> Freezing user space processes ... (elapsed 0.006 seconds) done.
>>>>>> OOM killer disabled.
>>>>>> Freezing remaining freezable tasks ... (elapsed 0.004 seconds) done.
>>>>>> Unable to handle kernel NULL pointer dereference at virtual address
>>>>>> 0000000000000070
>>>>>> Mem abort info:
>>>>>> ï¿½ï¿½ ï¿½ ESR = 0x96000006
>>>>>> ï¿½ï¿½ ï¿½ EC = 0x25: DABT (current EL), IL = 32 bits
>>>>>> ï¿½ï¿½ ï¿½ SET = 0, FnV = 0
>>>>>> ï¿½ï¿½ ï¿½ EA = 0, S1PTW = 0
>>>>>> ï¿½ï¿½ ï¿½ FSC = 0x06: level 2 translation fault
>>>>>> Data abort info:
>>>>>> ï¿½ï¿½ ï¿½ ISV = 0, ISS = 0x00000006
>>>>>> ï¿½ï¿½ ï¿½ CM = 0, WnR = 0
>>>>>> user pgtable: 4k pages, 48-bit VAs, pgdp=000000008ad08000
>>>>>> [0000000000000070] pgd=0800000085c3c003, p4d=0800000085c3c003,
>>>>>> pud=0800000088dcf003, pmd=0000000000000000
>>>>>> Internal error: Oops: 96000006 [#1] PREEMPT SMP
>>>>>> Modules linked in: bluetooth ecdh_generic ecc rfkill ipv6 ax88796b
>>>>>> venus_enc venus_dec videobuf2_dma_contig asix crct10dif_ce adv7511
>>>>>> snd_soc_msm8916_analog qcom_spmi_temp_alarm rtc_pm8xxx qcom_pon
>>>>>> qcom_camss qcom_spmi_vadc videobuf2_dma_sg qcom_vadc_common msm
>>>>>> venus_core v4l2_fwnode v4l2_async snd_soc_msm8916_digital
>>>>>> videobuf2_memops snd_soc_lpass_apq8016 snd_soc_lpass_cpu v4l2_mem2mem
>>>>>> snd_soc_lpass_platform snd_soc_apq8016_sbc videobuf2_v4l2
>>>>>> snd_soc_qcom_common qcom_rng videobuf2_common i2c_qcom_cci
>>>>>> qnoc_msm8916
>>>>>> videodev mc icc_smd_rpm mdt_loader socinfo display_connector rmtfs_mem
>>>>>> CPU: 1 PID: 1522 Comm: rtcwake Not tainted 5.13.0-next-20210629 #3592
>>>>>> Hardware name: Qualcomm Technologies, Inc. APQ 8016 SBC (DT)
>>>>>> pstate: 80000005 (Nzcv daif -PAN -UAO -TCO BTYPE=--)
>>>>>> pc : msm_runtime_suspend+0x1c/0x60 [msm]
>>>>>> lr : msm_pm_suspend+0x18/0x38 [msm]
>>>>>> ...
>>>>>> Call trace:
>>>>>> ï¿½ï¿½ ï¿½msm_runtime_suspend+0x1c/0x60 [msm]
>>>>>> ï¿½ï¿½ ï¿½msm_pm_suspend+0x18/0x38 [msm]
>>>>>> ï¿½ï¿½ ï¿½dpm_run_callback+0x84/0x378
>>>>> I wonder if we're missing a pm_runtime_disable() call on the failure
>>>>> path?
>>>>> i.e. something like the diff below...
>>>>
>>>> I've checked and it doesn't fix anything.
>>>
>>> What's happened previously? Has an IOMMU actually failed to probe, or
>>> is this a fiddly "code movement unveils latent bug elsewhere" kind of
>>> thing? There doesn't look to be much capable of going wrong in
>>> msm_runtime_suspend() itself, so is the DRM driver also in a broken
>>> half-probed state where it's left its pm_runtime_ops behind without
>>> its drvdata being valid?
>>>
>> I finally had some time to analyze this issue. It turned out that with
>> this patch, iommu fails to probe for soc:iommu@1f08000 device, while it
>> worked fine before. This happens because this patch adds a check for the
>> return value of the bus_set_iommu() in
>> drivers/iommu/arm/arm-smmu/qcom_iommu.c. When I removed that check, it
>> probes successfully again. It looks that there are already iommu ops
>> registered for platform bus, before qcom_iommu probes. On the other
>> hand, if I remember correctly they are not used during the device
>> registration, but they are needed for some legacy stuff. I can send a
>> patch restoring old code flow if you think that this is a right solution.
> 
> Yes, let's just revert the qcom_iommu.c changes from that patch for now.
> The pm runtime stuff looks dodgy anyway so I think this needs more thought.

Oh, right, blindly returning the -EBUSY from bus_set_iommu() because 
we're not the first instance to probe is definitely the wrong thing to 
do as well. It's still not clear why failing makes the DRM driver fall 
over, but +1 to qcom-iommu needing some deeper consideration.

Robin.