Re: [PATCH v10 15/24] drm/mediatek: Remove ineffectual power management codes

[AngeloGioacchino Del Regno]

Il 19/10/23 07:56, Hsiao Chien Sung ha scritto:

Display modules will be powered on when .atomic_enable(),
there is no need to do it again in mtk_crtc_ddp_hw_init().
Besides, the DRM devices are created manually when mtk-mmsys
is probed and there is no power domain linked to it.

Fixes: 119f5173628a ("drm/mediatek: Add DRM Driver for Mediatek SoC MT8173.")

Signed-off-by: Hsiao Chien Sung <shawn.s...@mediatek.com>
---
  drivers/gpu/drm/mediatek/mtk_drm_crtc.c | 18 +++---------------
  1 file changed, 3 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c 
b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
index bc4cc75cca18..c7edd80be428 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c
@@ -6,7 +6,6 @@
  #include <linux/clk.h>
  #include <linux/dma-mapping.h>
  #include <linux/mailbox_controller.h>
-#include <linux/pm_runtime.h>
  #include <linux/soc/mediatek/mtk-cmdq.h>
  #include <linux/soc/mediatek/mtk-mmsys.h>
  #include <linux/soc/mediatek/mtk-mutex.h>
@@ -362,22 +361,16 @@ static int mtk_crtc_ddp_hw_init(struct mtk_drm_crtc 
*mtk_crtc, struct drm_atomic
                drm_connector_list_iter_end(&conn_iter);
        }

- ret = pm_runtime_resume_and_get(crtc->dev->dev);

-       if (ret < 0) {
-               DRM_ERROR("Failed to enable power domain: %d\n", ret);
-               return ret;
-       }
-

Are you really sure that writes to DISP_REG_OVL_xxx and others in other modules,
called by the .layer_config() callback, can be successfully done on an unpowered
and/or unclocked module, on all MediaTek SoCs?
This looks a bit odd.

        ret = mtk_mutex_prepare(mtk_crtc->mutex);
        if (ret < 0) {
                DRM_ERROR("Failed to enable mutex clock: %d\n", ret);
-               goto err_pm_runtime_put;
+               goto error;
        }

ret = mtk_crtc_ddp_clk_enable(mtk_crtc);

        if (ret < 0) {
                DRM_ERROR("Failed to enable component clocks: %d\n", ret);
-               goto err_mutex_unprepare;
+               goto error;
        }

for (i = 0; i < mtk_crtc->ddp_comp_nr - 1; i++) {

@@ -426,16 +419,13 @@ static int mtk_crtc_ddp_hw_init(struct mtk_drm_crtc 
*mtk_crtc, struct drm_atomic

...because you could otherwise just call pm_runtime_put() here, instead of 
removing
the pm_runtime_resume_and_get() call, which is something I would advise to do.

Regards,
Angelo

        return 0;

-err_mutex_unprepare:

+error:
        mtk_mutex_unprepare(mtk_crtc->mutex);
-err_pm_runtime_put:
-       pm_runtime_put(crtc->dev->dev);
        return ret;
  }

static void mtk_crtc_ddp_hw_fini(struct mtk_drm_crtc *mtk_crtc)

  {
-       struct drm_device *drm = mtk_crtc->base.dev;
        struct drm_crtc *crtc = &mtk_crtc->base;
        int i;

@@ -465,8 +455,6 @@ static void mtk_crtc_ddp_hw_fini(struct mtk_drm_crtc *mtk_crtc)

        mtk_crtc_ddp_clk_disable(mtk_crtc);
        mtk_mutex_unprepare(mtk_crtc->mutex);

- pm_runtime_put(drm->dev);

-
        if (crtc->state->event && !crtc->state->active) {
                spin_lock_irq(&crtc->dev->event_lock);
                drm_crtc_send_vblank_event(crtc, crtc->state->event);