linux-kernel - Re: [linux-sunxi] [PATCH v2 5/9] drm/sun4i: tcon

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Message-ID: <CAMty3ZDRYBPKrGQxAZoB+trFiDLJ5BxDfNUOnPzgd+UWcpwCoQ@mail.gmail.com>
Date:   Mon, 17 Jun 2019 15:59:50 +0530
From:   Jagan Teki <jagan@...rulasolutions.com>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Maxime Ripard <maxime.ripard@...tlin.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Michael Trimarchi <michael@...rulasolutions.com>,
        linux-sunxi <linux-sunxi@...glegroups.com>,
        linux-amarula <linux-amarula@...rulasolutions.com>
Subject: Re: [linux-sunxi] [PATCH v2 5/9] drm/sun4i: tcon_top: Register clock
 gates in probe

On Sun, Jun 16, 2019 at 11:01 AM Chen-Yu Tsai <wens@...e.org> wrote:
>
> On Sat, Jun 15, 2019 at 12:44 AM Jagan Teki <jagan@...rulasolutions.com> wrote:
> >
> > TCON TOP have clock gates for TV0, TV1, dsi and right
> > now these are register during bind call.
> >
> > Of which, dsi clock gate would required during DPHY probe
> > but same can miss to get since tcon top is not bound at
> > that time.
> >
> > To solve, this circular dependency move the clock gate
> > registration from bind to probe so-that DPHY can get the
> > dsi gate clock on time.
> >
> > Signed-off-by: Jagan Teki <jagan@...rulasolutions.com>
> > ---
> >  drivers/gpu/drm/sun4i/sun8i_tcon_top.c | 94 ++++++++++++++------------
> >  1 file changed, 49 insertions(+), 45 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/sun4i/sun8i_tcon_top.c b/drivers/gpu/drm/sun4i/sun8i_tcon_top.c
> > index 465e9b0cdfee..a8978b3fe851 100644
> > --- a/drivers/gpu/drm/sun4i/sun8i_tcon_top.c
> > +++ b/drivers/gpu/drm/sun4i/sun8i_tcon_top.c
> > @@ -124,7 +124,53 @@ static struct clk_hw *sun8i_tcon_top_register_gate(struct device *dev,
> >  static int sun8i_tcon_top_bind(struct device *dev, struct device *master,
> >                                void *data)
> >  {
> > -       struct platform_device *pdev = to_platform_device(dev);
> > +       struct sun8i_tcon_top *tcon_top = dev_get_drvdata(dev);
> > +       int ret;
> > +
> > +       ret = reset_control_deassert(tcon_top->rst);
> > +       if (ret) {
> > +               dev_err(dev, "Could not deassert ctrl reset control\n");
> > +               return ret;
> > +       }
> > +
> > +       ret = clk_prepare_enable(tcon_top->bus);
> > +       if (ret) {
> > +               dev_err(dev, "Could not enable bus clock\n");
> > +               goto err_assert_reset;
> > +       }
>
> You have to de-assert the reset control and enable the clock before the
> clocks it provides are registered. Otherwise a consumer may come in and
> ask for the provided clock to be enabled, but since the TCON TOP's own
> reset and clock are still disabled, you can't actually access the registers
> that controls the provided clock.

These rst and bus are common reset and bus clocks not tcon top clocks
that are trying to register here. ie reason I have not moved it in
top.