linux-kernel - Re: [PATCH 4/8] drm/mediatek: dsi: add pdata variable to start clk in HS mode

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Date:   Thu, 22 Oct 2020 18:48:54 +0200
From:   Fabien Parent <fparent@...libre.com>
To:     Chun-Kuang Hu <chunkuang.hu@...nel.org>
Cc:     "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Philipp Zabel <p.zabel@...gutronix.de>
Subject: Re: [PATCH 4/8] drm/mediatek: dsi: add pdata variable to start clk in
 HS mode

Hi Chun-Kuang,

On Wed, Oct 21, 2020 at 7:07 PM Chun-Kuang Hu <chunkuang.hu@...nel.org> wrote:
>
> Hi, Fabien:
>
> Fabien Parent <fparent@...libre.com> 於 2020年10月21日 週三 上午1:43寫道：
> >
> > On MT8167, DSI seems to work fine only if we start the clk in HS mode.
> > If we don't start the clk in HS but try to switch later to HS, the
> > display does not work.
> >
> > This commit adds a platform data variable to be used to start the
> > DSI clk in HS mode at power on.
>
> This patch looks like a hack patch. If you cowork with Mediatek,
> please find out the correct solution or give a reasonable explanation.
> If you could not get help from Mediatek, I would wait for comment on
> this patch.

It seems that this workaround is because of a specific display and not
because of a specific issue of the MT8167 DSI IP. I will drop this
patch in v2.

> Regards,
> Chun-Kuang.
>
> >
> > Signed-off-by: Fabien Parent <fparent@...libre.com>
> > ---
> >  drivers/gpu/drm/mediatek/mtk_dsi.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c b/drivers/gpu/drm/mediatek/mtk_dsi.c
> > index 4a188a942c38..461643c05689 100644
> > --- a/drivers/gpu/drm/mediatek/mtk_dsi.c
> > +++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
> > @@ -175,6 +175,7 @@ struct mtk_dsi_driver_data {
> >         const u32 reg_cmdq_off;
> >         bool has_shadow_ctl;
> >         bool has_size_ctl;
> > +       bool use_hs_on_power_on;
> >  };
> >
> >  struct mtk_dsi {
> > @@ -671,7 +672,7 @@ static int mtk_dsi_poweron(struct mtk_dsi *dsi)
> >
> >         mtk_dsi_clk_ulp_mode_leave(dsi);
> >         mtk_dsi_lane0_ulp_mode_leave(dsi);
> > -       mtk_dsi_clk_hs_mode(dsi, 0);
> > +       mtk_dsi_clk_hs_mode(dsi, !!dsi->driver_data->use_hs_on_power_on);
> >
> >         return 0;
> >  err_disable_engine_clk:
> > --
> > 2.28.0
> >