Re: [PATCH v6 11/22] clk: sunxi-ng: a64: Add minimum rate for PLL_MIPI

Maxime Ripard
2019-07-20T09:32:02Z

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On Sat, Jul 20, 2019 at 12:46:27PM +0530, Jagan Teki wrote:
> On Sat, Jul 20, 2019 at 12:28 PM Maxime Ripard
> <maxime.ripard-LDxbnhwyfcJBDgjK7y7TUQ@public.gmane.org> wrote:
> >
> > On Thu, Jul 11, 2019 at 07:43:16PM +0200, Michael Nazzareno Trimarchi wrote:
> > > > > tcon-pixel clock is the rate that you want to achive on display side
> > > > > and if you have 4 lanes 32bit or lanes and different bit number that
> > > > > you need to have a clock that is able to put outside bits and speed
> > > > > equal to pixel-clock * bits / lanes. so If you want a pixel-clock of
> > > > > 40 mhz and you have 32bits and 4 lanes you need to have a clock of
> > > > > 40 * 32 / 4 in no-burst mode. I think that this is done but most of
> > > > > the display.
> > > >
> > > > So this is what the issue is then?
> > > >
> > > > This one does make sense, and you should just change the rate in the
> > > > call to clk_set_rate in sun4i_tcon0_mode_set_cpu.
> > > >
> > > > I'm still wondering why that hasn't been brought up in either the
> > > > discussion or the commit log before though.
> > > >
> > > Something like this?
> > >
> > > drivers/gpu/drm/sun4i/sun4i_tcon.c | 20 +++++++++++---------
> > > drivers/gpu/drm/sun4i/sun6i_mipi_dsi.h | 2 --
> > > 2 files changed, 11 insertions(+), 11 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > > b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > > index 64c43ee6bd92..42560d5c327c 100644
> > > --- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > > +++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > > @@ -263,10 +263,11 @@ static int sun4i_tcon_get_clk_delay(const struct
> > > drm_display_mode *mode,
> > > }
> > >
> > > static void sun4i_tcon0_mode_set_common(struct sun4i_tcon *tcon,
> > > - const struct drm_display_mode *mode)
> > > + const struct drm_display_mode *mode,
> > > + u32 tcon_mul)
> > > {
> > > /* Configure the dot clock */
> > > - clk_set_rate(tcon->dclk, mode->crtc_clock * 1000);
> > > + clk_set_rate(tcon->dclk, mode->crtc_clock * tcon_mul * 1000);
> > >
> > > /* Set the resolution */
> > > regmap_write(tcon->regs, SUN4I_TCON0_BASIC0_REG,
> > > @@ -335,12 +336,13 @@ static void sun4i_tcon0_mode_set_cpu(struct
> > > sun4i_tcon *tcon,
> > > u8 bpp = mipi_dsi_pixel_format_to_bpp(device->format);
> > > u8 lanes = device->lanes;
> > > u32 block_space, start_delay;
> > > - u32 tcon_div;
> > > + u32 tcon_div, tcon_mul;
> > >
> > > - tcon->dclk_min_div = SUN6I_DSI_TCON_DIV;
> > > - tcon->dclk_max_div = SUN6I_DSI_TCON_DIV;
> > > + tcon->dclk_min_div = 4;
> > > + tcon->dclk_max_div = 127;
> > >
> > > - sun4i_tcon0_mode_set_common(tcon, mode);
> > > + tcon_mul = bpp / lanes;
> > > + sun4i_tcon0_mode_set_common(tcon, mode, tcon_mul);
> > >
> > > /* Set dithering if needed */
> > > sun4i_tcon0_mode_set_dithering(tcon, sun4i_tcon_get_connector(encoder));
> > > @@ -366,7 +368,7 @@ static void sun4i_tcon0_mode_set_cpu(struct
> > > sun4i_tcon *tcon,
> > > */
> > > regmap_read(tcon->regs, SUN4I_TCON0_DCLK_REG, &tcon_div);
> > > tcon_div &= GENMASK(6, 0);
> > > - block_space = mode->htotal * bpp / (tcon_div * lanes);
> > > + block_space = mode->htotal * tcon_div * tcon_mul;
> > > block_space -= mode->hdisplay + 40;
> > >
> > > regmap_write(tcon->regs, SUN4I_TCON0_CPU_TRI0_REG,
> > > @@ -408,7 +410,7 @@ static void sun4i_tcon0_mode_set_lvds(struct
> > > sun4i_tcon *tcon,
> > >
> > > tcon->dclk_min_div = 7;
> > > tcon->dclk_max_div = 7;
> > > - sun4i_tcon0_mode_set_common(tcon, mode);
> > > + sun4i_tcon0_mode_set_common(tcon, mode, 1);
> > >
> > > /* Set dithering if needed */
> > > sun4i_tcon0_mode_set_dithering(tcon, sun4i_tcon_get_connector(encoder));
> > > @@ -487,7 +489,7 @@ static void sun4i_tcon0_mode_set_rgb(struct
> > > sun4i_tcon *tcon,
> > >
> > > tcon->dclk_min_div = 6;
> > > tcon->dclk_max_div = 127;
> > > - sun4i_tcon0_mode_set_common(tcon, mode);
> > > + sun4i_tcon0_mode_set_common(tcon, mode, 1);
> > >
> > > /* Set dithering if needed */
> > > sun4i_tcon0_mode_set_dithering(tcon, connector);
> > > diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.h
> > > b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.h
> > > index 5c3ad5be0690..a07090579f84 100644
> > > --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.h
> > > +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.h
> > > @@ -13,8 +13,6 @@
> > > #include <drm/drm_encoder.h>
> > > #include <drm/drm_mipi_dsi.h>
> > >
> > > -#define SUN6I_DSI_TCON_DIV 4
> > > -
> > > struct sun6i_dsi {
> > > struct drm_connector connector;
> > > struct drm_encoder encoder;
> >
> > I had more something like this in mind:
> > http://code.bulix.org/nlp5a4-803511
>
> Worth to look at it. was it working on your panel? meanwhile I will check it.

I haven't tested it.

> We have updated with below change [1], seems working on but is
> actually checking the each divider as before start with 4... till 127.
>
> This new approach, is start looking the best divider from 4.. based on
> the idea vs rounded it will ended up best divider like [2]

But why?

I mean, it's not like it's the first time I'm asking this...

If the issue is what Micheal described, then the divider has nothing
to do with it. We've had that discussion over and over again.

So you need to come with some argument and proof that the divider of
that clock need to change. Otherwise, stop trying to make that happen:
it won't.

Maxime

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Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering