linux-kernel - Re: [PATCH] drm: mxsfb: fix runtime PM handling

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Message-ID: <90d16681-2a7a-4826-0411-478353d2afe3@denx.de>
Date:   Fri, 13 Jul 2018 11:12:48 +0200
From:   Marek Vasut <marex@...x.de>
To:     Anson Huang <anson.huang@....com>,
        "airlied@...ux.ie" <airlied@...ux.ie>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     dl-linux-imx <linux-imx@....com>, Stefan Agner <stefan@...er.ch>
Subject: Re: [PATCH] drm: mxsfb: fix runtime PM handling

On 07/13/2018 11:06 AM, Anson Huang wrote:
[...]
>>
>> On 07/13/2018 10:54 AM, Anson Huang wrote:
>>> As display power domain is combined with lcdif node on some i.MX
>>> platforms like i.MX6SL, when lcdif driver is enabled, the mxsfb_load
>>> is called to enable runtime pm, and a pair of pm_runtime_get_sync and
>>> pm_runtime_put_sync are also called, that will cause generic power
>>> domain driver to disable lcdif power domain and lcdif is no longer
>>> working, the lcdif power should ONLY be turned off when display is
>>> disabled, so move the pm_runtime_put_sync to mxsfb_unload and remove
>>> the pm_runtime_get_sync in mxsfb_unload as well, in this way, when
>>> display is enabled, the lcdif power will be always ON until the
>>> display is disabled.
>>>
>>> Signed-off-by: Anson Huang <Anson.Huang@....com>
>>
>> Doesn't this also mean the block will always be on, thus wasting power ?
>  
> I think drm driver should have somewhere to implement the display
> disable case, like when fb0 is blank (echo 1 > /sys/class/graphics/fb0/blank),

Isn't this just the fbdev emulation on top of drm/kms ?
I think this stuff can be compiled out completely.

> then lcdif can be powered gated, and
> when display is back on (unblank), lcdif needs to be re-initialization and display will
> be on, current implementation is incorrect, with kernel booting up, lcdif
> is NOT working at all.

It works fine on MX6SX , so I think this is isolated to MX6SL ?
I'm CCing Stefan, he might have some valuable feedback here.

> The runtime power gating case can be implemented later to save power,
> need lcdif experts to do it. Thanks.
> 
> Anson.
> 
>>
>>> ---
>>>  drivers/gpu/drm/mxsfb/mxsfb_drv.c | 3 +--
>>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_drv.c
>>> b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
>>> index ffe5137..1ba179b 100644
>>> --- a/drivers/gpu/drm/mxsfb/mxsfb_drv.c
>>> +++ b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
>>> @@ -235,7 +235,6 @@ static int mxsfb_load(struct drm_device *drm,
>>> unsigned long flags)
>>>
>>>  	pm_runtime_get_sync(drm->dev);
>>>  	ret = drm_irq_install(drm, platform_get_irq(pdev, 0));
>>> -	pm_runtime_put_sync(drm->dev);
>>>
>>>  	if (ret < 0) {
>>>  		dev_err(drm->dev, "Failed to install IRQ handler\n"); @@ -264,6
>>> +263,7 @@ static int mxsfb_load(struct drm_device *drm, unsigned long
>>> flags)
>>>  err_irq:
>>>  	drm_panel_detach(mxsfb->panel);
>>>  err_vblank:
>>> +	pm_runtime_put_sync(drm->dev);
>>>  	pm_runtime_disable(drm->dev);
>>>
>>>  	return ret;
>>> @@ -279,7 +279,6 @@ static void mxsfb_unload(struct drm_device *drm)
>>>  	drm_kms_helper_poll_fini(drm);
>>>  	drm_mode_config_cleanup(drm);
>>>
>>> -	pm_runtime_get_sync(drm->dev);
>>>  	drm_irq_uninstall(drm);
>>>  	pm_runtime_put_sync(drm->dev);
>>>
>>>
>>
>>
>> --
>> Best regards,
>> Marek Vasut


-- 
Best regards,
Marek Vasut