Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <1607591262-21736-1-git-send-email-yongqiang.niu@mediatek.com>
 <1607591262-21736-6-git-send-email-yongqiang.niu@mediatek.com>
 <CAAOTY_-aYFz1Xg6r2ur+BF_k_35F3qNLLb16_2c0MaMsYre-+w@mail.gmail.com> <1607647514.12750.5.camel@mhfsdcap03>
In-Reply-To: <1607647514.12750.5.camel@mhfsdcap03>
From:   Chun-Kuang Hu <chunkuang.hu@kernel.org>
Date:   Mon, 14 Dec 2020 22:54:15 +0800
Message-ID: <CAAOTY__HA95WLNppOKainvsZCxA6Wv3edLyvOW6FxAjUos=afQ@mail.gmail.com>
Subject: Re: [PATCH v8, 5/6] drm/mediatek: add RDMA fifo size error handle
To:     Yongqiang Niu <yongqiang.niu@mediatek.com>
Cc:     Chun-Kuang Hu <chunkuang.hu@kernel.org>,
        CK Hu <ck.hu@mediatek.com>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Rob Herring <robh+dt@kernel.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Mark Rutland <mark.rutland@arm.com>,
        DTML <devicetree@vger.kernel.org>,
        David Airlie <airlied@linux.ie>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        DRI Development <dri-devel@lists.freedesktop.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@lists.infradead.org>,
        Daniel Vetter <daniel@ffwll.ch>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

Hi, Yongqiang:

Yongqiang Niu <yongqiang.niu@mediatek.com> =E6=96=BC 2020=E5=B9=B412=E6=9C=
=8811=E6=97=A5 =E9=80=B1=E4=BA=94 =E4=B8=8A=E5=8D=888:45=E5=AF=AB=E9=81=93=
=EF=BC=9A
>
> On Thu, 2020-12-10 at 23:50 +0800, Chun-Kuang Hu wrote:
> > Hi, Yongqiang:
> >
> > Yongqiang Niu <yongqiang.niu@mediatek.com> =E6=96=BC 2020=E5=B9=B412=E6=
=9C=8810=E6=97=A5 =E9=80=B1=E5=9B=9B =E4=B8=8B=E5=8D=885:08=E5=AF=AB=E9=81=
=93=EF=BC=9A
> > >
> > > This patch add RDMA fifo size error handle
> > > rdma fifo size will not always bigger than the calculated threshold
> > > if that case happened, we need set fifo size as the threshold
> > >
> > > Signed-off-by: Yongqiang Niu <yongqiang.niu@mediatek.com>
> > > ---
> > >  drivers/gpu/drm/mediatek/mtk_disp_rdma.c | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/mediatek/mtk_disp_rdma.c b/drivers/gpu/d=
rm/mediatek/mtk_disp_rdma.c
> > > index 794acc5..0508392 100644
> > > --- a/drivers/gpu/drm/mediatek/mtk_disp_rdma.c
> > > +++ b/drivers/gpu/drm/mediatek/mtk_disp_rdma.c
> > > @@ -151,6 +151,10 @@ static void mtk_rdma_config(struct mtk_ddp_comp =
*comp, unsigned int width,
> > >          * account for blanking, and with a pixel depth of 4 bytes:
> > >          */
> > >         threshold =3D width * height * vrefresh * 4 * 7 / 1000000;
> > > +
> > > +       if (threshold > rdma_fifo_size)
> > > +               threshold =3D rdma_fifo_size;
> >
> > If the formula is not correct, you should fix the formula not work arou=
nd.
> >
> > Regards,
> > Chun-Kuang.
>
> how about this:
> threshold =3D max(width * height * vrefresh * 4 * 7 / 1000000,
> rdma_fifo_size);

When I use width =3D 1920, height =3D 1080, vrefresh =3D 60 to calculate, I
get threshold =3D 2985.
So I think set threshold to half of fifo size is OK for MAX_WIDTH,
MAX_HEIGHT, MAX_VREFRESH (these three may be different in each SoC)

threshold =3D RDMA_FIFO_PSEUDO_SIZE(rdma_fifo_size) / 2;

But I worry half fifo size is too big for small resolution and let
small resolution too easy to trigger burst read DRAM. So let the
formula to be this:

threshold =3D RDMA_FIFO_PSEUDO_SIZE(rdma_fifo_size) * width * height *
vrefresh / 2 / MAX_WIDTH / MAX_HEIGHT / MAX_VREFRESH;

How do you think about this?

Regards,
Chun-Kuang.

> >
> > > +
> > >         reg =3D RDMA_FIFO_UNDERFLOW_EN |
> > >               RDMA_FIFO_PSEUDO_SIZE(rdma_fifo_size) |
> > >               RDMA_OUTPUT_VALID_FIFO_THRESHOLD(threshold);
> > > --
> > > 1.8.1.1.dirty
> > > _______________________________________________
> > > Linux-mediatek mailing list
> > > Linux-mediatek@lists.infradead.org
> > > http://lists.infradead.org/mailman/listinfo/linux-mediatek
>