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

From: Michael Nazzareno Trimarchi
Date: Fri Aug 02 2019 - 04:38:59 EST

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Hi Maxime

On Mon, Jul 29, 2019 at 8:59 AM Michael Nazzareno Trimarchi
<michael@xxxxxxxxxxxxxxxxxxxx> 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
>
> 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.
>

diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c
b/drivers/gpu/drm/sun4i/sun4i_tcon.c
index 94f24c5e2dc5..ffb7906054e5 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
@@ -338,8 +338,9 @@ static void sun4i_tcon0_mode_set_cpu(struct
sun4i_tcon *tcon,
u32 block_space, start_delay;
u32 tcon_div;

- tcon->dclk_min_div = bpp/lanes;
- tcon->dclk_max_div = bpp/lanes;
+ tcon->dclk_min_div = 4;
+ tcon->dclk_max_div = 127;
+ clk_set_rate_exclusive(tcon->sclk0, mode->crtc_clock * 1000 * bpp / lanes);

sun4i_tcon0_mode_set_common(tcon, mode);

Something like this on top of jagan proposal

Michael

> 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
>
>
>
> --
> | Michael Nazzareno Trimarchi Amarula Solutions BV |
> | COO - Founder Cruquiuskade 47 |
> | +31(0)851119172 Amsterdam 1018 AM NL |
> | [`as] http://www.amarulasolutions.com |

--
| Michael Nazzareno Trimarchi Amarula Solutions BV |
| COO - Founder Cruquiuskade 47 |
| +31(0)851119172 Amsterdam 1018 AM NL |
| [`as] http://www.amarulasolutions.com |

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