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

[AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>]

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@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.
> 
> 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@collabora.com>

>>
>>>    	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