linux-kernel - Re: [PATCH v3 8/8] drm/mediatek: add third ddp path

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Date:   Mon, 28 May 2018 10:26:57 +0800
From:   Stu Hsieh <stu.hsieh@...iatek.com>
To:     CK Hu <ck.hu@...iatek.com>
CC:     Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...ux.ie>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        <dri-devel@...ts.freedesktop.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>, <srv_heupstream@...iatek.com>
Subject: Re: [PATCH v3 8/8] drm/mediatek: add third ddp path

Hi, CK:
I've some idea as below.

On Fri, 2018-05-25 at 13:00 +0800, CK Hu wrote:
> Hi, Stu:
> 
> On Fri, 2018-05-25 at 10:34 +0800, stu.hsieh@...iatek.com wrote:
> > From: Stu Hsieh <stu.hsieh@...iatek.com>
> > 
> > This patch create third crtc by third ddp path
> > 
> 
> Apply this patch before the patch 'Add support for mediatek SOC MT2712'
> because this patch is necessary for mt2712.
> 
> > Signed-off-by: Stu Hsieh <stu.hsieh@...iatek.com>
> > ---
> >  drivers/gpu/drm/mediatek/mtk_drm_drv.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> > index b32c4cc8d051..3a866e1d6af4 100644
> > --- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> > +++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> > @@ -267,6 +267,11 @@ static int mtk_drm_kms_init(struct drm_device *drm)
> >  	if (ret < 0)
> >  		goto err_component_unbind;
> >  
> > +	ret = mtk_drm_crtc_create(drm, private->data->third_path,
> > +				  private->data->third_len);
> 
> I think you should prevent doing this for mt8173 and mt2701 because that
> two SoC has only two ddp path.

Now, 8173 and 2701 have only two ddp path, there is a problem on run
time. 
There are three crtc for drm resource, and there is nothing in third
crtc. 
Because 8173 and 2701 have no third ddp, and the third ddp_len is zero.
So, I want to add the condition like following in mtk_crtc_create()
if (path_len == 0)
	return 0;

Then, the valur ret is zero and it would not create the null third crtc.


Regards,
Stu

> 
> Regards,
> CK
> 
> > +	if (ret < 0)
> > +		goto err_component_unbind;
> > +
> >  	/* Use OVL device for all DMA memory allocations */
> >  	np = private->comp_node[private->data->main_path[0]] ?:
> >  	     private->comp_node[private->data->ext_path[0]];
> 
>