Date:   Mon, 29 Jul 2019 08:59:04 +0200
From:   Michael Nazzareno Trimarchi <michael@...rulasolutions.com>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     Jagan Teki <jagan@...rulasolutions.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, Chen-Yu Tsai <wens@...e.org>,
        Michael Turquette <mturquette@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-amarula <linux-amarula@...rulasolutions.com>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [PATCH v6 11/22] clk: sunxi-ng: a64: Add minimum rate for PLL_MIPI

Hi

On Wed, Jul 24, 2019 at 11:05 AM Maxime Ripard
<maxime.ripard@...tlin.com> wrote:
>
> On Mon, Jul 22, 2019 at 03:51:04PM +0530, Jagan Teki wrote:
> > Hi Maxime,
> >
> > On Sat, Jul 20, 2019 at 3:02 PM Maxime Ripard <maxime.ripard@...tlin.com> wrote:
> > >
> > > 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@...tlin.com> 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.
> >
> > This is what Michael is mentioned in above mail "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. "
>
> Yeah, so we need to change the clock rate.
>
> > He is trying to manage the bpp/lanes into dclk_mul (in last mail)
> > and it can multiply with pixel clock which is rate argument in
> > sun4i_dclk_round_rate.
> >
> > The solution I have mentioned in dclk_min, max is bpp/lanes also
> > multiple rate in dotclock sun4i_dclk_round_rate.
> >
> > In both cases the overall pll_rate depends on dividers, the one that I
> > have on this patch is based on BSP and the Michael one is more generic
> > way so-that it can not to touch other functionalities and looping
> > dividers to find the best one.
> >
> > If dclk_min/max is bpp/lanes then dotclock directly using divider 6
> > (assuming 24-bit and 4 lanes) and return the pll_rate and divider 6
> > associated.
> >
> > if dclk_mul is bpp/lanes, on Michael new change, the dividers start
> > with 4 and end with 127 but the constant ideal rate which rate *
> > bpp/lanes but the loop from sun4i_dclk_round_rate computed the divider
> > as 6 only, ie what I'm mentioned on the above mail.
>
> We've been over this a couple of times already.
>
> The clock is generated like this:
>
> PLL -> TCON Module Clock -> TCON DCLK
>
> You want the TCON DCLK to be at the pixel clock rate * bpp /
> lanes. Fine, that makes sense.
>
> Except that the patch you've sent, instead of changing the rate
> itself, changes the ratio between the module clock and DCLK.
>
> And this is where the issue lies. First, from a logical viewpoint, it
> doesn't make sense. If you want to change the clock rate, then just do
> it. Don't hack around the multipliers trying to fall back to something
> that works for you.
>
> Then, the ratio itself needs to be set to 4. This is the part that
> we've discussed way too many times already, but in the Allwinner BSP,
> that ratio is hardcoded to 4, and we've had panels that need it at
> that value.
>
> So, what you want to do is to have:
>
> TCON DCLK = pixel clock * bpp / lanes
> TCON Module Clock = DCLK * 4
> PLL = Module Clock * Module Clock Divider (which I believe is 1 in most cases)

  pll-mipi                       1        1        1   178200000
   0     0  50000
          tcon0                       2        2        1   178200000
        0     0  50000
             tcon-pixel-clock         1        1        1    29700000
        0     0  50000

This is an english problem from my side:
tcon-pixel-clock is DCLK
tcon0 must be tcon-pixel-clock * bpp / lanes because the logic need to
put a bit every cycle.

One solution can be:
- set_rate_exclusive to tcon0 and calculate as display pixel clock *
bpp  / lanes
- calculate the tcon-pixel-clock using all divider

Problem is that the function that calculate tcon-pixel-clock does not
have any constrain on the ideal value. What you are
suggesting is not correct in my opinion or I'm not following your
suggesstion. What I know is that if we have a pixel-clock
of dvi display of 50Mhz and we have 4 lanes 32bit we need a clock in
the logic of 400Mhz (this is the ideal throughtput).
So tcon-pixel-clock is 50mhz and tcon0 is 400Mhz.

Michael


>
> So you want to increase the PLL. Fortunately for use, this is exactly
> what a call to clk_set_rate will end up doing.
>
> Maxime
>
> --
> Maxime Ripard, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com



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| Michael Nazzareno Trimarchi                     Amarula Solutions BV |
| COO  -  Founder                                      Cruquiuskade 47 |
| +31(0)851119172                                 Amsterdam 1018 AM NL |
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