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

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Date:   Mon, 28 Jan 2019 15:06:10 +0530
From:   Jagan Teki <jagan@...rulasolutions.com>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     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>,
        Michael Trimarchi <michael@...rulasolutions.com>,
        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

On Sat, Jan 26, 2019 at 2:54 AM Maxime Ripard <maxime.ripard@...tlin.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@...rulasolutions.com>
> > Acked-by: Stephen Boyd <sboyd@...nel.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.

Since the above min_rate is not desired for possible panels clock, I
think we can rely on BSP to make a move here. I'm planning to do these
changes in next version.

Let me know if you have any comments here?

[1] https://patchwork.kernel.org/patch/10777519/