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

[AngeloGioacchino Del Regno]

Il 19/10/23 11:52, Shawn Sung (宋孝謙) ha scritto:
> Hi Angelo,
>
> On Thu, 2023-10-19 at 11:07 +0200, AngeloGioacchino Del Regno wrote:
> > 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@xxxxxxxxxxxx>
> > > ---
> > >    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.
>
> Not sure if I get your point correctly. We removed this PM API because:
>
> 1. mtk_crtc_ddp_hw_init() is called by mtk_drm_crtc_atomic_enable(),
> and the new inline function mtk_ddp_comp_power_on() is called before hw
> init, we can make sure the power is on before configuring the hardware.
>
> 2. The device "crtc->dev->dev" here is assigned by the probe function
> of mtk-mmsys, which will be look like "mediatek-drm.auto.13", and this
> device is not linked to any power domain.

Thanks for the clarification. In this case:

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>

> > >    	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
>
> Thanks,
> Shawn