Re: [PATCH] drm/msm: Switch ordering of runpm put vs devfreq_idle

[Akhil P Oommen <akhilpo@codeaurora.org>]

On 9/27/2021 8:59 PM, Rob Clark wrote:
> From: Rob Clark <robdclark@chromium.org>
> 
> I've seen a few crashes like:
> 
>      Internal error: synchronous external abort: 96000010 [#1] PREEMPT SMP
>      Modules linked in: snd_seq_dummy snd_seq snd_seq_device bridge stp llc tun nf_nat_tftp nf_conntrack_tftp nf_nat_ftp nf_conntrack_ftp esp6 ah6 ip6t_REJECT ip6t_ipv6header vhost_vsock vhost vmw_vsock_virtio_transport_common vsock rfcomm algif_hash algif_skcipher af_alg uinput veth xt_cgroup xt_MASQUERADE venus_enc venus_dec videobuf2_dma_contig qcom_spmi_adc5 qcom_spmi_adc_tm5 hci_uart qcom_vadc_common cros_ec_typec qcom_spmi_temp_alarm typec btqca snd_soc_rt5682_i2c snd_soc_rt5682 snd_soc_sc7180 bluetooth snd_soc_qcom_common snd_soc_rl6231 ecdh_generic ecc venus_core v4l2_mem2mem snd_soc_lpass_sc7180 snd_soc_lpass_hdmi snd_soc_lpass_cpu snd_soc_lpass_platform snd_soc_max98357a ip6table_nat fuse iio_trig_sysfs cros_ec_lid_angle cros_ec_sensors cros_ec_sensors_core industrialio_triggered_buffer kfifo_buf cros_ec_sensorhub lzo_rle ath10k_snoc lzo_compress ath10k_core ath zram mac80211 cfg80211 ax88179_178a usbnet mii uvcvideo videobuf2_vmalloc joydev
>      CPU: 3 PID: 212 Comm: A618-worker Tainted: G W 5.4.139-16300-g88d8e1285982 #1
>      Hardware name: Google Pompom (rev1) with LTE (DT)
>      pstate: 60c00009 (nZCv daif +PAN +UAO)
>      pc : a6xx_gmu_set_oob+0x114/0x200
>      lr : a6xx_gmu_set_oob+0x10c/0x200
>      sp : ffffffc011b7bc20
>      x29: ffffffc011b7bc20 x28: ffffffdad27c5000
>      x27: 0000000000000001 x26: ffffffdad1521044
>      x25: ffffffbef7498338 x24: 0000000000000018
>      x23: 0000000000000002 x22: 0000000000014648
>      x21: 0000033732fe638b x20: 0000000080000000
>      x19: ffffffbef7433bc8 x18: 0000000040000000
>      x17: 000000243508d982 x16: 000000000000b67e
>      x15: 00000000000090d4 x14: 0000000000000024
>      x13: 0000000000000024 x12: 0000000000017521
>      x11: 0000000000000b48 x10: 0000000000326a48
>      x9 : 1a130d33f6371600 x8 : ffffffc011e54648
>      x7 : 614948e00005003c x6 : ffffffbe3cd17e60
>      x5 : 0000000000000040 x4 : 0000000000000004
>      x3 : 0000000000000000 x2 : ffffffbef7488000
>      x1 : ffffffbef7488000 x0 : 0000000000000000
>      Call trace:
>      a6xx_gmu_set_oob+0x114/0x200
>      a6xx_gmu_set_freq+0xe0/0x1fc
>      msm_devfreq_target+0x80/0x13c
>      msm_devfreq_idle+0x54/0x94
>      retire_submit+0x170/0x254
>      retire_submits+0xa4/0xdc
>      retire_worker+0x1c/0x28
>      kthread_worker_fn+0xf4/0x1bc
>      kthread+0x140/0x158
>      ret_from_fork+0x10/0x18
>      Code: 52800c81 9415bbe5 f9400a68 8b160108 (b9400108)
>      ---[ end trace 16b871df2482cd61 ]---
>      Kernel panic - not syncing: Fatal exception
>      SMP: stopping secondary CPUs
>      Kernel Offset: 0x1ac1400000 from 0xffffffc010000000
>      PHYS_OFFSET: 0xffffffc280000000
>      CPU features: 0x88102e,2a80aa38
>      Memory Limit: none
> 
> Which smells a lot like touching hw after power collapse.  I'm not
> *entirely* sure how it could have taken 66ms (the autosuspend delay)
> before we get to a6xx_gmu_set_oob(), but to be safe we should move
> the pm_runtime_put_autosuspend() after msm_devfreq_idle().
https://elixir.bootlin.com/linux/v5.15-rc1/source/drivers/gpu/drm/msm/adreno/a6xx_gmu.c#L132
We have this check in the gmu freq set path which should avoid this 
scenario. I might be a bit pedantic here, but I feel that the original 
code is more accurate. We should immediately mark last busy and put 
runtime_pm refcount.

-Akhil.

> 
> Fixes: 9bc95570175a ("drm/msm: Devfreq tuning")
> Signed-off-by: Rob Clark <robdclark@chromium.org>
> ---
>   drivers/gpu/drm/msm/msm_gpu.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c
> index d1a16642ecd5..2b2bbe7499e6 100644
> --- a/drivers/gpu/drm/msm/msm_gpu.c
> +++ b/drivers/gpu/drm/msm/msm_gpu.c
> @@ -667,9 +667,6 @@ static void retire_submit(struct msm_gpu *gpu, struct msm_ringbuffer *ring,
>   
>   	msm_submit_retire(submit);
>   
> -	pm_runtime_mark_last_busy(&gpu->pdev->dev);
> -	pm_runtime_put_autosuspend(&gpu->pdev->dev);
> -
>   	spin_lock_irqsave(&ring->submit_lock, flags);
>   	list_del(&submit->node);
>   	spin_unlock_irqrestore(&ring->submit_lock, flags);
> @@ -683,6 +680,9 @@ static void retire_submit(struct msm_gpu *gpu, struct msm_ringbuffer *ring,
>   	mutex_unlock(&gpu->active_lock);
>   
>   	msm_gem_submit_put(submit);
> +
> +	pm_runtime_mark_last_busy(&gpu->pdev->dev);
> +	pm_runtime_put_autosuspend(&gpu->pdev->dev);
>   }
>   
>   static void retire_submits(struct msm_gpu *gpu)
>