linux-kernel - Re: [v1] drm/msm/dpu: update reservations in commit path

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Date:   Tue, 4 Aug 2020 12:32:29 -0700
From:   Rob Clark <robdclark@...il.com>
To:     Kalyan Thota <kalyan_t@...eaurora.org>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Sean Paul <seanpaul@...omium.org>,
        "Kristian H. Kristensen" <hoegsberg@...omium.org>,
        Douglas Anderson <dianders@...omium.org>,
        Krishna Manikandan <mkrishn@...eaurora.org>,
        Raviteja Tamatam <travitej@...eaurora.org>,
        nganji@...eaurora.org, Stephen Boyd <swboyd@...omium.org>,
        Abhinav Kumar <abhinavk@...eaurora.org>,
        Drew Davenport <ddavenport@...omium.org>
Subject: Re: [v1] drm/msm/dpu: update reservations in commit path

On Tue, Aug 4, 2020 at 4:32 AM Kalyan Thota <kalyan_t@...eaurora.org> wrote:
>
> DPU resources reserved in the atomic_check path gets unwinded
> during modeset operation before commit happens in a non seamless
> transition.
>
> Update the reservations in the commit path to avoid resource
> failures. Secondly have dummy reservations in atomic_check path
> so that we can gracefully fail the composition if resources are
> not available.
>
> Signed-off-by: Kalyan Thota <kalyan_t@...eaurora.org>
> ---
>  drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> index 63976dc..c6b8254 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> @@ -565,7 +565,7 @@ static int dpu_encoder_virt_atomic_check(
>         const struct drm_display_mode *mode;
>         struct drm_display_mode *adj_mode;
>         struct msm_display_topology topology;
> -       struct dpu_global_state *global_state;
> +       struct dpu_global_state tmp_resv_state;
>         int i = 0;
>         int ret = 0;
>
> @@ -582,7 +582,7 @@ static int dpu_encoder_virt_atomic_check(
>         dpu_kms = to_dpu_kms(priv->kms);
>         mode = &crtc_state->mode;
>         adj_mode = &crtc_state->adjusted_mode;
> -       global_state = dpu_kms_get_existing_global_state(dpu_kms);
> +       memset(&tmp_resv_state, 0, sizeof(tmp_resv_state));

I think what you want to do is dpu_kms_get_global_state().. that will
clone/duplicate the existing global state (or return the already
duplicated global state if it is called multiple times).

It is safe to modify this global state in the atomic_check() path.. in
fact that is the intention.  For a TEST_ONLY atomic commit, or if any
of the atomic_check()'s fail, this new duplicated global state is
discarded.  If all the checks succeed and the atomic update is
committed to hw, this new global state replaces the existing global
state.

BR,
-R

>         trace_dpu_enc_atomic_check(DRMID(drm_enc));
>
>         /*
> @@ -621,7 +621,7 @@ static int dpu_encoder_virt_atomic_check(
>                  * info may not be available to complete reservation.
>                  */
>                 if (drm_atomic_crtc_needs_modeset(crtc_state)) {
> -                       ret = dpu_rm_reserve(&dpu_kms->rm, global_state,
> +                       ret = dpu_rm_reserve(&dpu_kms->rm, &tmp_resv_state,
>                                         drm_enc, crtc_state, topology);
>                 }
>         }
> @@ -966,7 +966,7 @@ static void dpu_encoder_virt_mode_set(struct drm_encoder *drm_enc,
>         struct dpu_hw_blk *hw_lm[MAX_CHANNELS_PER_ENC];
>         struct dpu_hw_blk *hw_dspp[MAX_CHANNELS_PER_ENC] = { NULL };
>         int num_lm, num_ctl, num_pp, num_dspp;
> -       int i, j;
> +       int i, j, rc;
>
>         if (!drm_enc) {
>                 DPU_ERROR("invalid encoder\n");
> @@ -1006,6 +1006,13 @@ static void dpu_encoder_virt_mode_set(struct drm_encoder *drm_enc,
>
>         topology = dpu_encoder_get_topology(dpu_enc, dpu_kms, adj_mode);
>
> +       rc = dpu_rm_reserve(&dpu_kms->rm, global_state, drm_enc,
> +               drm_crtc->state, topology);
> +       if (rc) {
> +               DPU_ERROR_ENC(dpu_enc, "Failed to reserve resources\n");
> +               return;
> +       }
> +
>         /* Query resource that have been reserved in atomic check step. */
>         num_pp = dpu_rm_get_assigned_resources(&dpu_kms->rm, global_state,
>                 drm_enc->base.id, DPU_HW_BLK_PINGPONG, hw_pp,
> --
> 1.9.1
>