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

[Jagan Teki <jagan@amarulasolutions.com>]

On Tue, Jan 29, 2019 at 8:43 PM Maxime Ripard <maxime.ripard@bootlin.com> wrote:
>
> On Mon, Jan 28, 2019 at 03:06:10PM +0530, Jagan Teki wrote:
> > On Sat, Jan 26, 2019 at 2:54 AM Maxime Ripard <maxime.ripard@bootlin.com> wrote:
> > >
> > > On Fri, Jan 25, 2019 at 01:28:49AM +0530, Jagan Teki wrote:
> > > > Minimum PLL used for MIPI is 500MHz, as per manual, but
> > > > lowering the min rate by 300MHz can result proper working
> > > > nkms divider with the help of desired dclock rate from
> > > > panel driver.
> > > >
> > > > Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
> > > > Acked-by: Stephen Boyd <sboyd@kernel.org>
> > >
> > > Going 200MHz below the minimum doesn't seem really reasonable. What
> > > is the issue that you are trying to fix here?
> > >
> > > It looks like it's picking bad dividers, but if that's the case, this
> > > isn't the proper fix.
> >
> > As I stated in earlier patches, the whole idea is pick the desired
> > dclk divider based dclk rate. So the dotclock, sun4i_dclk_round_rate
> > is unable to get the proper dclk divider at the end, so it eventually
> > picking up wrong divider value and fired vblank timeout.
> >
> > So, we come-up with optimal and working min_rate 300MHz in pll-mipi to
> > get the desired clock something like below.
> > [    2.415773] [drm] No driver support for vblank timestamp query.
> > [    2.424116] sun4i_dclk_round_rate: min_div = 4 max_div = 127, rate = 55000000
> > [    2.424172] ideal = 220000000, rounded = 0
> > [    2.424176] ideal = 275000000, rounded = 0
> > [    2.424194] ccu_nkm_round_rate: rate = 330000000
> > [    2.424197] ideal = 330000000, rounded = 330000000
> > [    2.424201] sun4i_dclk_round_rate: div = 6 rate = 55000000
> > [    2.424205] sun4i_dclk_round_rate: min_div = 4 max_div = 127, rate = 55000000
> > [    2.424209] ideal = 220000000, rounded = 0
> > [    2.424213] ideal = 275000000, rounded = 0
> > [    2.424230] ccu_nkm_round_rate: rate = 330000000
> > [    2.424233] ideal = 330000000, rounded = 330000000
> > [    2.424236] sun4i_dclk_round_rate: div = 6 rate = 55000000
> > [    2.424253] ccu_nkm_round_rate: rate = 330000000
> > [    2.424270] ccu_nkm_round_rate: rate = 330000000
> > [    2.424278] sun4i_dclk_recalc_rate: val = 1, rate = 330000000
> > [    2.424281] sun4i_dclk_recalc_rate: val = 1, rate = 330000000
> > [    2.424306] ccu_nkm_set_rate: rate = 330000000, parent_rate = 297000000
> > [    2.424309] ccu_nkm_set_rate: _nkm.n = 5
> > [    2.424311] ccu_nkm_set_rate: _nkm.k = 2
> > [    2.424313] ccu_nkm_set_rate: _nkm.m = 9
> > [    2.424661] sun4i_dclk_set_rate div 6
> > [    2.424668] sun4i_dclk_recalc_rate: val = 6, rate = 55000000
> >
> > But look like this wouldn't valid for all other dclock rates, say BPI
> > panel has 30MHz clock that would failed with this logic.
> >
> > On the other side Allwinner BSP calculating dclk divider based on the
> > SoC's. for A33 [1] it is fixed dclk divider of 4 and for A64 is is
> > calculated based on the bpp/lanes.
>
> It looks like the A64 has the same divider of 4:
> https://github.com/BPI-SINOVOIP/BPI-M64-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp2/disp/de/lowlevel_sun50iw1/de_dsi.c#L12
>
> I think you're confusing it with the ratio between the pixel clock and
> the dotclock, called dsi_div:
> https://github.com/BPI-SINOVOIP/BPI-M64-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp2/disp/de/lowlevel_sun50iw1/disp_al.c#L198

Ahh.. I thought this initially but as far as DSI clock computation is
concern, the L12 tcon_div is local variable which is used for edge0
computation in burst mode and not for the dsi clock computation. Since
the BSP is unable to get the tcon_div during edge0 computation, they
defined it locally I think.

You can see the lcd_clk_config() code [2], where we can see DSI clock
computation using dsi_div value.

Here is dump after the in Line 792 which is after computation[3]
[   10.800737] lcd_clk_config: dsi_div = 6, tcon_div = 4, lcd_div = 1
[   10.800743] lcd_clk_config: lcd_dclk_freq = 55, dclk_rate = 55000000
[   10.800749] lcd_clk_config: lcd_rate = 330000000, pll_rate = 330000000

The above dump the lcd_rate 330MHz is computed with panel clock, 55MHz
into dsi_div 6. So this can be our actual divider values dclk_min_div,
dclk_max_div in sun4i_dclk_round_rate (from
drivers/gpu/drm/sun4i/sun4i_dotclock.c)

We can even confirm this from Mainline code:
[    1.866128] sun4i_dclk_round_rate: min_div = 6 max_div = 6, rate = 55000000
[    1.873112] round_rate, parent = 330000000
[    1.877351] round_rate, rate = 330000000
[    1.881338] ideal = 330000000, rounded = 330000000, div = 6
[    1.887232] sun4i_dclk_round_rate: div = 6 rate = 55000000
[    1.887239] sun4i_dclk_round_rate: min_div = 6 max_div = 6, rate = 55000000
[    1.887243] round_rate, parent = 330000000
[    1.887259] round_rate, rate = 330000000
[    1.887264] ideal = 330000000, rounded = 330000000, div = 6
[    1.887267] sun4i_dclk_round_rate: div = 6 rate = 55000000
[    1.887270] round_rate, parent = 330000000
[    1.887286] round_rate, rate = 330000000
[    1.887292] round_rate, parent = 330000000
[    1.887307] round_rate, rate = 330000000
[    1.887320] sun4i_dclk_recalc_rate: val = 1, rate = 330000000
[    1.887324] sun4i_dclk_recalc_rate: val = 1, rate = 330000000
[    1.887350] rate = 330000000
[    1.887353] parent_rate = 297000000
[    1.887355] reg = 0x80c00000
[    1.887359] _nkm.n = 5, nkm->n.offset = 0x1, nkm->n.shift = 8
[    1.887362] _nkm.k = 2, nkm->k.offset = 0x1, nkm->k.shift = 4
[    1.887365] _nkm.m = 9, nkm->m.offset = 0x1, nkm->m.shift = 0
[    1.887712] sun4i_dclk_set_rate div 6
[    1.887720] sun4i_dclk_recalc_rate: val = 6, rate = 55000000

So, the dsi_div from AW BSP is our dclk_mini_div(and dclk_max_div) and
that can be computed as format/lanes in A64.

Hope this explaining clears the diff, let me know if I miss anything.

[2] https://github.com/BPI-SINOVOIP/BPI-M64-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp2/disp/de/disp_lcd.c#L781
[3] https://github.com/BPI-SINOVOIP/BPI-M64-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp2/disp/de/disp_lcd.c#L792

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