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

From: Michael Nazzareno Trimarchi
Date: Thu Aug 15 2019 - 08:26:14 EST

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In reply to: Maxime Ripard: "Re: [PATCH v6 11/22] clk: sunxi-ng: a64: Add minimum rate for PLL_MIPI"
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Hi Maxime

On Tue, Aug 13, 2019 at 8:05 AM Maxime Ripard <maxime.ripard@xxxxxxxxxxx> wrote:
>
> On Mon, Jul 29, 2019 at 08:59:04AM +0200, Michael Nazzareno Trimarchi wrote:
> > Hi
> >
> > On Wed, Jul 24, 2019 at 11:05 AM Maxime Ripard
> > <maxime.ripard@xxxxxxxxxxx> 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@xxxxxxxxxxx> 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@xxxxxxxxxxx> 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
>
> Is this before or after your patches?
>

This is just an example of clock tree to be clear to everyone how they
are connected

> > 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.
>
> Again, I'm not saying this is wrong, but each time I've looked at it
> the BSP was using a 4 divider between the tcon module clock and the
> dotclock.
>

We have tested on 4-5 displays. Well I don't care on bsp but I care
about if it works
and if other SoC has similar approach on clock calculation.

> So, please prove me wrong here.
>

Having only 10 pages of documentation is a bit difficult.

> > One solution can be:
> > - set_rate_exclusive to tcon0 and calculate as display pixel clock *
> > bpp / lanes
>
> I'm not sure what set_rate_exclusive has to do with it. I mean, it's a
> good idea to use it, but it shouldn't really change anything to the
> discussion.

Well, this will just do a minimal change on source code and put the constrains
to the tcon0

>
> > - calculate the tcon-pixel-clock using all divider
>
> I'm not sure what you mean by that.
>
> > Problem is that the function that calculate tcon-pixel-clock does not
> > have any constrain on the ideal value.
>
> It does have constraints, but you're right that it will not try to
> find an exact match and bail out if it can't do it, but will find the
> closest match.
>

We need to find the closest divider that match the pixel clock and be close
to the ideal tcon0 rate.

> > What you are suggesting is not correct in my opinion or I'm not
> > following your suggesstion.
>
> Then prove me wrong.
>
> > 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.
>
> There's one thing to keep in mind though. The TCON dotclock in the
> MIPI-DSI case isn't directly tied to the Bit Clock, it's simply an
> internal clock in the pipeline to feed the FIFO of the MIPI-DSI
> controller. The MIPI-DSI controller itself will generate that clock,
> and only that one will have those constraints.
>

I have done the same thinking but because it works for us seems that
somehow is used
to internal logic too

Michael

> Maxime
>
> --
> Maxime Ripard, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com

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In reply to: Maxime Ripard: "Re: [PATCH v6 11/22] clk: sunxi-ng: a64: Add minimum rate for PLL_MIPI"
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