linux-kernel - Re: [14/23] drm/sun4i: Create minimal multipliers and dividers

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Date:   Tue, 24 Oct 2017 13:12:18 +1100
From:   Jonathan Liu <net147@...il.com>
To:     Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:     Daniel Vetter <daniel.vetter@...el.com>,
        David Airlie <airlied@...ux.ie>, Chen-Yu Tsai <wens@...e.org>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        Priit Laes <plaes@...es.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Quentin Schulz <quentin.schulz@...e-electrons.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mylene Josserand <mylene.josserand@...e-electrons.com>,
        linux-clk@...r.kernel.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        icenowy@...c.io
Subject: Re: [14/23] drm/sun4i: Create minimal multipliers and dividers

Hi Maxime,

On 17 October 2017 at 20:06, Maxime Ripard
<maxime.ripard@...e-electrons.com> wrote:
> The various outputs the TCON can provide have different constraints on the
> dotclock divider. Let's make them configurable by the various mode_set
> functions.
>
> Signed-off-by: Maxime Ripard <maxime.ripard@...e-electrons.com>
> Reviewed-by: Chen-Yu Tsai <wens@...e.org>
> ---
>  drivers/gpu/drm/sun4i/sun4i_dotclock.c | 10 +++++++---
>  drivers/gpu/drm/sun4i/sun4i_tcon.c     |  2 ++
>  drivers/gpu/drm/sun4i/sun4i_tcon.h     |  2 ++
>  3 files changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/sun4i/sun4i_dotclock.c b/drivers/gpu/drm/sun4i/sun4i_dotclock.c
> index d401156490f3..023f39bda633 100644
> --- a/drivers/gpu/drm/sun4i/sun4i_dotclock.c
> +++ b/drivers/gpu/drm/sun4i/sun4i_dotclock.c
> @@ -17,8 +17,9 @@
>  #include "sun4i_dotclock.h"
>
>  struct sun4i_dclk {
> -       struct clk_hw   hw;
> -       struct regmap   *regmap;
> +       struct clk_hw           hw;
> +       struct regmap           *regmap;
> +       struct sun4i_tcon       *tcon;
>  };
>
>  static inline struct sun4i_dclk *hw_to_dclk(struct clk_hw *hw)
> @@ -73,11 +74,13 @@ static unsigned long sun4i_dclk_recalc_rate(struct clk_hw *hw,
>  static long sun4i_dclk_round_rate(struct clk_hw *hw, unsigned long rate,
>                                   unsigned long *parent_rate)
>  {
> +       struct sun4i_dclk *dclk = hw_to_dclk(hw);
> +       struct sun4i_tcon *tcon = dclk->tcon;
>         unsigned long best_parent = 0;
>         u8 best_div = 1;
>         int i;
>
> -       for (i = 6; i <= 127; i++) {
> +       for (i = tcon->dclk_min_div; i <= tcon->dclk_max_div; i++) {
>                 unsigned long ideal = rate * i;
>                 unsigned long rounded;
>
> @@ -167,6 +170,7 @@ int sun4i_dclk_create(struct device *dev, struct sun4i_tcon *tcon)
>         dclk = devm_kzalloc(dev, sizeof(*dclk), GFP_KERNEL);
>         if (!dclk)
>                 return -ENOMEM;
> +       dclk->tcon = tcon;
>
>         init.name = clk_name;
>         init.ops = &sun4i_dclk_ops;
> diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> index f69bcdf11cb8..3efa1ab045cd 100644
> --- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> +++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> @@ -177,6 +177,8 @@ static void sun4i_tcon0_mode_set_rgb(struct sun4i_tcon *tcon,
>         u8 clk_delay;
>         u32 val = 0;
>
> +       tcon->dclk_min_div = 6;
> +       tcon->dclk_max_div = 127;
>         sun4i_tcon0_mode_set_common(tcon, mode);
>
>         /* Adjust clock delay */
> diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.h b/drivers/gpu/drm/sun4i/sun4i_tcon.h
> index f61bf6d83b4a..4141fbd97ddf 100644
> --- a/drivers/gpu/drm/sun4i/sun4i_tcon.h
> +++ b/drivers/gpu/drm/sun4i/sun4i_tcon.h
> @@ -169,6 +169,8 @@ struct sun4i_tcon {
>
>         /* Pixel clock */
>         struct clk                      *dclk;
> +       u8                              dclk_max_div;
> +       u8                              dclk_min_div;
>
>         /* Reset control */
>         struct reset_control            *lcd_rst;

I have 4.3" RGB LCD enabled on sun7i-a20-olinuxino-lime and hdmi
disabled. After applying this patch the LCD no longer turns on.
If I add some debug statements to sun4i_dclk_recalc_rate, it shows
tcon->dclk_min_div and tcon->dclk_max_div are both 0.

Regards,
Jonathan