linux-kernel - Re: [PATCH v6 04/10] drm/msm/dp: Add basic PSR support for eDP

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Date:   Thu, 28 Jul 2022 17:20:05 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Vinod Polimera <quic_vpolimer@...cinc.com>
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>, LKML <linux-kernel@...r.kernel.org>,
        Rob Clark <robdclark@...il.com>,
        Stephen Boyd <swboyd@...omium.org>,
        quic_kalyant <quic_kalyant@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        "Kuogee Hsieh (QUIC)" <quic_khsieh@...cinc.com>,
        quic_vproddut <quic_vproddut@...cinc.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        "Aravind Venkateswaran (QUIC)" <quic_aravindh@...cinc.com>,
        "Abhinav Kumar (QUIC)" <quic_abhinavk@...cinc.com>,
        Sankeerth Billakanti <quic_sbillaka@...cinc.com>
Subject: Re: [PATCH v6 04/10] drm/msm/dp: Add basic PSR support for eDP

Hi,

On Mon, Jul 11, 2022 at 5:57 AM Vinod Polimera
<quic_vpolimer@...cinc.com> wrote:
>
> @@ -359,6 +367,24 @@ void dp_catalog_ctrl_lane_mapping(struct dp_catalog *dp_catalog)
>                         ln_mapping);
>  }
>
> +void dp_catalog_ctrl_psr_mainlink_enable(struct dp_catalog *dp_catalog,
> +                                               bool enable)
> +{
> +       u32 val;
> +       struct dp_catalog_private *catalog = container_of(dp_catalog,
> +                               struct dp_catalog_private, dp_catalog);
> +
> +       val = dp_read_link(catalog, REG_DP_MAINLINK_CTRL);
> +       val &= ~DP_MAINLINK_CTRL_ENABLE;

nit: the line above is useless. Remove. In the case that you're
enabling you're just adding the bit back in. In the case that you're
disabling you're doing the exact same operation below.


> @@ -610,6 +636,47 @@ void dp_catalog_ctrl_hpd_config(struct dp_catalog *dp_catalog)
>         dp_write_aux(catalog, REG_DP_DP_HPD_CTRL, DP_DP_HPD_CTRL_HPD_EN);
>  }
>
> +static void dp_catalog_enable_sdp(struct dp_catalog_private *catalog)
> +{
> +       /* trigger sdp */
> +       dp_write_link(catalog, MMSS_DP_SDP_CFG3, UPDATE_SDP);
> +       dp_write_link(catalog, MMSS_DP_SDP_CFG3, !UPDATE_SDP);

!UPDATE_SDP is a really counter-intuitive way to say 0x0.


> @@ -645,6 +712,20 @@ u32 dp_catalog_hpd_get_intr_status(struct dp_catalog *dp_catalog)
>         return isr & (mask | ~DP_DP_HPD_INT_MASK);
>  }
>
> +int dp_catalog_ctrl_read_psr_interrupt_status(struct dp_catalog *dp_catalog)

Why is the return type "int" and not "u32". It's a hardware register.
It's u32 here. The caller assigns it to a u32.


> +void dp_ctrl_set_psr(struct dp_ctrl *dp_ctrl, bool enter)
> +{
> +       struct dp_ctrl_private *ctrl = container_of(dp_ctrl,
> +                       struct dp_ctrl_private, dp_ctrl);
> +
> +       if (!ctrl->panel->psr_cap.version)
> +               return;
> +
> +       /*
> +        * When entering PSR,
> +        * 1. Send PSR enter SDP and wait for the PSR_UPDATE_INT
> +        * 2. Turn off video
> +        * 3. Disable the mainlink
> +        *
> +        * When exiting PSR,
> +        * 1. Enable the mainlink
> +        * 2. Send the PSR exit SDP
> +        */
> +       if (enter) {
> +               reinit_completion(&ctrl->psr_op_comp);
> +               dp_catalog_ctrl_set_psr(ctrl->catalog, true);
> +
> +               if (!wait_for_completion_timeout(&ctrl->psr_op_comp,
> +                       PSR_OPERATION_COMPLETION_TIMEOUT_JIFFIES)) {
> +                       DRM_ERROR("PSR_ENTRY timedout\n");
> +                       dp_catalog_ctrl_set_psr(ctrl->catalog, false);
> +                       return;
> +               }
> +
> +               dp_catalog_ctrl_state_ctrl(ctrl->catalog, 0);
> +
> +               dp_catalog_ctrl_psr_mainlink_enable(ctrl->catalog, false);
> +       } else {
> +               dp_catalog_ctrl_psr_mainlink_enable(ctrl->catalog, true);
> +
> +               dp_catalog_ctrl_set_psr(ctrl->catalog, false);

My PSR knowledge is not very strong, but I do remember a recent commit
from Brian Norris fly by for the Analogix controller. See commit
c4c6ef229593 ("drm/bridge: analogix_dp: Make PSR-exit block less").

In that commit it sounds as if we need to wait for _something_ (resync
I guess?) here and not just return instantly.


> @@ -388,6 +388,8 @@ static int dp_display_process_hpd_high(struct dp_display_private *dp)
>
>         edid = dp->panel->edid;
>
> +       dp->dp_display.psr_supported = !!dp->panel->psr_cap.version;
> +

nit: remove the "!!". You're already storing this in a "bool" which
will handle this for you.


> +static const struct drm_bridge_funcs edp_bridge_ops = {
> +       .atomic_enable = edp_bridge_atomic_enable,
> +       .atomic_disable = edp_bridge_atomic_disable,
> +       .atomic_post_disable = edp_bridge_atomic_post_disable,
> +       .mode_set = dp_bridge_mode_set,
> +       .mode_valid = dp_bridge_mode_valid,
> +       .atomic_reset = drm_atomic_helper_bridge_reset,
> +       .atomic_duplicate_state = drm_atomic_helper_bridge_duplicate_state,
> +       .atomic_destroy_state = drm_atomic_helper_bridge_destroy_state,
> +       .atomic_check = edp_bridge_atomic_check,
> +};

nit: the location of your new functions is a little weird. You've got:

1. DP functions
2. eDP functions
3. eDP structure
4. DP structure

I'd expect:

1. DP functions
2. DP structure
3. eDP functions
4. eDP structure

-Doug