Re: [PATCH] of/device: add blacklist for iommu dma_ops

[Marek Szyprowski <m.szyprowski@samsung.com>]

Hi Tomasz,

On 2018-12-03 01:10, Tomasz Figa wrote:
> On Sat, Dec 1, 2018 at 8:54 AM Rob Clark <robdclark@gmail.com> wrote:
>> This solves a problem we see with drm/msm, caused by getting
>> iommu_dma_ops while we attach our own domain and manage it directly at
>> the iommu API level:
>>
>>   [0000000000000038] user address but active_mm is swapper
>>   Internal error: Oops: 96000005 [#1] PREEMPT SMP
>>   Modules linked in:
>>   CPU: 7 PID: 70 Comm: kworker/7:1 Tainted: G        W         4.19.3 #90
>>   Hardware name: xxx (DT)
>>   Workqueue: events deferred_probe_work_func
>>   pstate: 80c00009 (Nzcv daif +PAN +UAO)
>>   pc : iommu_dma_map_sg+0x7c/0x2c8
>>   lr : iommu_dma_map_sg+0x40/0x2c8
>>   sp : ffffff80095eb4f0
>>   x29: ffffff80095eb4f0 x28: 0000000000000000
>>   x27: ffffffc0f9431578 x26: 0000000000000000
>>   x25: 00000000ffffffff x24: 0000000000000003
>>   x23: 0000000000000001 x22: ffffffc0fa9ac010
>>   x21: 0000000000000000 x20: ffffffc0fab40980
>>   x19: ffffffc0fab40980 x18: 0000000000000003
>>   x17: 00000000000001c4 x16: 0000000000000007
>>   x15: 000000000000000e x14: ffffffffffffffff
>>   x13: ffff000000000000 x12: 0000000000000028
>>   x11: 0101010101010101 x10: 7f7f7f7f7f7f7f7f
>>   x9 : 0000000000000000 x8 : ffffffc0fab409a0
>>   x7 : 0000000000000000 x6 : 0000000000000002
>>   x5 : 0000000100000000 x4 : 0000000000000000
>>   x3 : 0000000000000001 x2 : 0000000000000002
>>   x1 : ffffffc0f9431578 x0 : 0000000000000000
>>   Process kworker/7:1 (pid: 70, stack limit = 0x0000000017d08ffb)
>>   Call trace:
>>    iommu_dma_map_sg+0x7c/0x2c8
>>    __iommu_map_sg_attrs+0x70/0x84
>>    get_pages+0x170/0x1e8
>>    msm_gem_get_iova+0x8c/0x128
>>    _msm_gem_kernel_new+0x6c/0xc8
>>    msm_gem_kernel_new+0x4c/0x58
>>    dsi_tx_buf_alloc_6g+0x4c/0x8c
>>    msm_dsi_host_modeset_init+0xc8/0x108
>>    msm_dsi_modeset_init+0x54/0x18c
>>    _dpu_kms_drm_obj_init+0x430/0x474
>>    dpu_kms_hw_init+0x5f8/0x6b4
>>    msm_drm_bind+0x360/0x6c8
>>    try_to_bring_up_master.part.7+0x28/0x70
>>    component_master_add_with_match+0xe8/0x124
>>    msm_pdev_probe+0x294/0x2b4
>>    platform_drv_probe+0x58/0xa4
>>    really_probe+0x150/0x294
>>    driver_probe_device+0xac/0xe8
>>    __device_attach_driver+0xa4/0xb4
>>    bus_for_each_drv+0x98/0xc8
>>    __device_attach+0xac/0x12c
>>    device_initial_probe+0x24/0x30
>>    bus_probe_device+0x38/0x98
>>    deferred_probe_work_func+0x78/0xa4
>>    process_one_work+0x24c/0x3dc
>>    worker_thread+0x280/0x360
>>    kthread+0x134/0x13c
>>    ret_from_fork+0x10/0x18
>>   Code: d2800004 91000725 6b17039f 5400048a (f9401f40)
>>   ---[ end trace f22dda57f3648e2c ]---
>>   Kernel panic - not syncing: Fatal exception
>>   SMP: stopping secondary CPUs
>>   Kernel Offset: disabled
>>   CPU features: 0x0,22802a18
>>   Memory Limit: none
>>
>> The problem is that when drm/msm does it's own iommu_attach_device(),
>> now the domain returned by iommu_get_domain_for_dev() is drm/msm's
>> domain, and it doesn't have domain->iova_cookie.
>>
>> We kind of avoided this problem prior to sdm845/dpu because the iommu
>> was attached to the mdp node in dt, which is a child of the toplevel
>> mdss node (which corresponds to the dev passed in dma_map_sg()).  But
>> with sdm845, now the iommu is attached at the mdss level so we hit the
>> iommu_dma_ops in dma_map_sg().
>>
>> But auto allocating/attaching a domain before the driver is probed was
>> already a blocking problem for enabling per-context pagetables for the
>> GPU.  This problem is also now solved with this patch.
>>
>> Fixes: 97890ba9289c dma-mapping: detect and configure IOMMU in of_dma_configure
>> Tested-by: Douglas Anderson <dianders@chromium.org>
>> Signed-off-by: Rob Clark <robdclark@gmail.com>
>> ---
>> This is an alternative/replacement for [1].  What it lacks in elegance
>> it makes up for in practicality ;-)
>>
>> [1] https://patchwork.freedesktop.org/patch/264930/
>>
>>  drivers/of/device.c | 22 ++++++++++++++++++++++
>>  1 file changed, 22 insertions(+)
>>
>> diff --git a/drivers/of/device.c b/drivers/of/device.c
>> index 5957cd4fa262..15ffee00fb22 100644
>> --- a/drivers/of/device.c
>> +++ b/drivers/of/device.c
>> @@ -72,6 +72,14 @@ int of_device_add(struct platform_device *ofdev)
>>         return device_add(&ofdev->dev);
>>  }
>>
>> +static const struct of_device_id iommu_blacklist[] = {
>> +       { .compatible = "qcom,mdp4" },
>> +       { .compatible = "qcom,mdss" },
>> +       { .compatible = "qcom,sdm845-mdss" },
>> +       { .compatible = "qcom,adreno" },
>> +       {}
>> +};
>> +
>>  /**
>>   * of_dma_configure - Setup DMA configuration
>>   * @dev:       Device to apply DMA configuration
>> @@ -164,6 +172,20 @@ int of_dma_configure(struct device *dev, struct device_node *np, bool force_dma)
>>         dev_dbg(dev, "device is%sbehind an iommu\n",
>>                 iommu ? " " : " not ");
>>
>> +       /*
>> +        * There is at least one case where the driver wants to directly
>> +        * manage the IOMMU, but if we end up with iommu dma_ops, that
>> +        * interferes with the drivers ability to use dma_map_sg() for
>> +        * cache operations.  Since we don't currently have a better
>> +        * solution, and this code runs before the driver is probed and
>> +        * has a chance to intervene, use a simple blacklist to avoid
>> +        * ending up with iommu dma_ops:
>> +        */
>> +       if (of_match_device(iommu_blacklist, dev)) {
>> +               dev_dbg(dev, "skipping iommu hookup\n");
>> +               iommu = NULL;
>> +       }
>> +
>>         arch_setup_dma_ops(dev, dma_addr, size, iommu, coherent);
>>
>>         return 0;
>> --
>> 2.19.2
>>
> +Marek Szyprowski who I believe had a similar problem with Exynos DRM before.
>
> Reviewed-by: Tomasz Figa <tfiga@chromium.org>


Thanks for adding me. So far Exynos DRM use other workaround, see commit
1feda5eb77fc ("drm/exynos: Use selected dma_dev default iommu domain
instead of a fake one"). Here is the link to the thread with more
comments and background:
https://www.spinics.net/lists/arm-kernel/msg676100.html

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland