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

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Message-ID: <5a059ca0-fcb7-4730-a0d8-29103fb71d54@collabora.com>
Date:   Thu, 19 Oct 2023 11:07:42 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Hsiao Chien Sung <shawn.sung@...iatek.com>,
        CK Hu <ck.hu@...iatek.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Rob Herring <robh+dt@...nel.org>
Cc:     Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, Fei Shao <fshao@...omium.org>,
        Sean Paul <sean@...rly.run>,
        Johnson Wang <johnson.wang@...iatek.corp-partner.google.com>,
        "Nancy . Lin" <nancy.lin@...iatek.com>,
        Moudy Ho <moudy.ho@...iatek.com>,
        "Jason-JH . Lin" <jason-jh.lin@...iatek.com>,
        Nathan Lu <nathan.lu@...iatek.com>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v10 15/24] drm/mediatek: Remove ineffectual power
 management codes

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.sung@...iatek.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);