[PATCH v3 2/2] drm/msm/dpu: Add mutex lock in control vblank irq
Dmitry Baryshkov
dmitry.baryshkov at linaro.org
Fri Dec 1 08:34:50 UTC 2023
On Fri, 1 Dec 2023 at 05:47, Bjorn Andersson <quic_bjorande at quicinc.com> wrote:
>
> On Thu, Nov 30, 2023 at 05:40:55PM -0800, Paloma Arellano wrote:
> > Add a missing mutex lock to control vblank irq. Thus prevent race
> > conditions when registering/unregistering the irq callback.
> >
>
> I'm guessing that the mutex is needed because vblank_refcount, while
> being an atomic_t, doesn't actually provide any protection during
> concurrency?
>
> I also tried to follow the calls backwards, but I'm uncertain how you
> end up here concurrently.
>
> When wrapped in proper mutual exclusion, can't vblank_refcount just be
> turned into an "int"...given that you're not actually able to rely on
> it's atomic behavior anyways...
>
>
> So, please rewrite the commit message with a detailed description of how
> the concurrency happens, and please review if vblank_refcount should be
> an atomic at all...
>
> > v2: Slightly changed wording of commit message
> > v3: Mistakenly did not change wording in last version. It is done now.
> >
> > Signed-off-by: Paloma Arellano <quic_parellan at quicinc.com>
> > ---
> > drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 6 ++++++
> > drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys.h | 6 ++++++
> > drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_cmd.c | 2 ++
> > drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c | 2 ++
> > 4 files changed, 16 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> > index 1cf7ff6caff4e..19ff7d1d5ccad 100644
> > --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> > +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> > @@ -119,6 +119,8 @@ enum dpu_enc_rc_states {
> > * Virtual encoder defers as much as possible to the physical encoders.
> > * Virtual encoder registers itself with the DRM Framework as the encoder.
> > * @base: drm_encoder base class for registration with DRM
> > + * @vblank_ctl_lock: Vblank ctl mutex lock to protect physical encoder
> > + * for IRQ purposes
>
> I think this protects vblank_refcount, so state that instead of the
> vague "for IRQ purposes".
>
> > * @enc_spinlock: Virtual-Encoder-Wide Spin Lock for IRQ purposes
> > * @enabled: True if the encoder is active, protected by enc_lock
> > * @num_phys_encs: Actual number of physical encoders contained.
> > @@ -166,6 +168,7 @@ enum dpu_enc_rc_states {
> > */
> > struct dpu_encoder_virt {
> > struct drm_encoder base;
> > + struct mutex vblank_ctl_lock;
> > spinlock_t enc_spinlock;
> >
> > bool enabled;
> > @@ -2255,6 +2258,7 @@ static int dpu_encoder_setup_display(struct dpu_encoder_virt *dpu_enc,
> > phys_params.dpu_kms = dpu_kms;
> > phys_params.parent = &dpu_enc->base;
> > phys_params.enc_spinlock = &dpu_enc->enc_spinlock;
> > + phys_params.vblank_ctl_lock = &dpu_enc->vblank_ctl_lock;
> >
> > WARN_ON(disp_info->num_of_h_tiles < 1);
> >
> > @@ -2386,6 +2390,7 @@ struct drm_encoder *dpu_encoder_init(struct drm_device *dev,
> > dpu_enc->enabled = false;
> > mutex_init(&dpu_enc->enc_lock);
> > mutex_init(&dpu_enc->rc_lock);
> > + mutex_init(&dpu_enc->vblank_ctl_lock);
>
> Is this somehow propagated to multiple different dpu_encoder_phys
> instances, or why do you need to initialize it here and pass the pointer
> through 2 different intermediate structures before assigning it to
> phys_enc->vblank_ctl_lock below?
Yes, there can be two phys_enc instances for a single encoder, so this
part is fine.
>
> >
> > ret = dpu_encoder_setup_display(dpu_enc, dpu_kms, disp_info);
> > if (ret)
> > @@ -2495,6 +2500,7 @@ void dpu_encoder_phys_init(struct dpu_encoder_phys *phys_enc,
> > phys_enc->dpu_kms = p->dpu_kms;
> > phys_enc->split_role = p->split_role;
> > phys_enc->enc_spinlock = p->enc_spinlock;
> > + phys_enc->vblank_ctl_lock = p->vblank_ctl_lock;
>
> Could you not just mutex_init() the one and only vblank_ctl_lock here?
>
> > phys_enc->enable_state = DPU_ENC_DISABLED;
> >
> > atomic_set(&phys_enc->vblank_refcount, 0);
> > diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys.h b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys.h
> > index 6f04c3d56e77c..5691bf6b82ee6 100644
> > --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys.h
> > +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys.h
> > @@ -155,6 +155,8 @@ enum dpu_intr_idx {
> > * @hw_wb: Hardware interface to the wb registers
> > * @dpu_kms: Pointer to the dpu_kms top level
> > * @cached_mode: DRM mode cached at mode_set time, acted on in enable
> > + * @vblank_ctl_lock: Vblank ctl mutex lock to protect physical encoder
> > + * for IRQ purposes
>
> Same here.
>
> > * @enabled: Whether the encoder has enabled and running a mode
> > * @split_role: Role to play in a split-panel configuration
> > * @intf_mode: Interface mode
> > @@ -183,6 +185,7 @@ struct dpu_encoder_phys {
> > struct dpu_hw_wb *hw_wb;
> > struct dpu_kms *dpu_kms;
> > struct drm_display_mode cached_mode;
> > + struct mutex *vblank_ctl_lock;
> > enum dpu_enc_split_role split_role;
> > enum dpu_intf_mode intf_mode;
> > spinlock_t *enc_spinlock;
> > @@ -253,6 +256,8 @@ struct dpu_encoder_phys_cmd {
> > * @split_role: Role to play in a split-panel configuration
> > * @hw_intf: Hardware interface to the intf registers
> > * @hw_wb: Hardware interface to the wb registers
> > + * @vblank_ctl_lock: Vblank ctl mutex lock to protect physical encoder
> > + * for IRQ purposes
>
> And here...
>
> Regards,
> Bjorn
>
> > * @enc_spinlock: Virtual-Encoder-Wide Spin Lock for IRQ purposes
> > */
> > struct dpu_enc_phys_init_params {
> > @@ -261,6 +266,7 @@ struct dpu_enc_phys_init_params {
> > enum dpu_enc_split_role split_role;
> > struct dpu_hw_intf *hw_intf;
> > struct dpu_hw_wb *hw_wb;
> > + struct mutex *vblank_ctl_lock;
> > spinlock_t *enc_spinlock;
> > };
> >
> > diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_cmd.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_cmd.c
> > index 25babfe1f001a..dcf1f6a18ad6e 100644
> > --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_cmd.c
> > +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_cmd.c
> > @@ -244,6 +244,7 @@ static int dpu_encoder_phys_cmd_control_vblank_irq(
> > return -EINVAL;
> > }
> >
> > + mutex_lock(phys_enc->vblank_ctl_lock);
> > refcount = atomic_read(&phys_enc->vblank_refcount);
> >
> > /* Slave encoders don't report vblank */
> > @@ -275,6 +276,7 @@ static int dpu_encoder_phys_cmd_control_vblank_irq(
> > }
> >
> > end:
> > + mutex_unlock(phys_enc->vblank_ctl_lock);
> > if (ret) {
> > DRM_ERROR("vblank irq err id:%u pp:%d ret:%d, enable %s/%d\n",
> > DRMID(phys_enc->parent),
> > diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
> > index 8e905d7267f9f..87bb49763785d 100644
> > --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
> > +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_vid.c
> > @@ -364,6 +364,7 @@ static int dpu_encoder_phys_vid_control_vblank_irq(
> > int ret = 0;
> > int refcount;
> >
> > + mutex_lock(phys_enc->vblank_ctl_lock);
> > refcount = atomic_read(&phys_enc->vblank_refcount);
> >
> > /* Slave encoders don't report vblank */
> > @@ -394,6 +395,7 @@ static int dpu_encoder_phys_vid_control_vblank_irq(
> > }
> >
> > end:
> > + mutex_unlock(phys_enc->vblank_ctl_lock);
> > if (ret) {
> > DRM_ERROR("failed: id:%u intf:%d ret:%d enable:%d refcnt:%d\n",
> > DRMID(phys_enc->parent),
> > --
> > 2.41.0
> >
> >
--
With best wishes
Dmitry
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