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    SubjectRe: [linux-sunxi] Re: [PATCH v2 11/27] drm/sun4i: tcon: Add support for tcon-top gate
    On Sat, Jun 16, 2018 at 1:33 AM, Jernej Škrabec <jernej.skrabec@siol.net> wrote:
    > Dne petek, 15. junij 2018 ob 19:13:17 CEST je Chen-Yu Tsai napisal(a):
    >> On Sat, Jun 16, 2018 at 12:41 AM, Jernej Škrabec
    >>
    >> <jernej.skrabec@siol.net> wrote:
    >> > Hi,
    >> >
    >> > Dne petek, 15. junij 2018 ob 10:31:10 CEST je Maxime Ripard napisal(a):
    >> >> Hi,
    >> >>
    >> >> On Tue, Jun 12, 2018 at 10:00:20PM +0200, Jernej Skrabec wrote:
    >> >> > TV TCONs connected to TCON TOP have to enable additional gate in order
    >> >> > to work.
    >> >> >
    >> >> > Add support for such TCONs.
    >> >> >
    >> >> > Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
    >> >> > ---
    >> >> >
    >> >> > drivers/gpu/drm/sun4i/sun4i_tcon.c | 11 +++++++++++
    >> >> > drivers/gpu/drm/sun4i/sun4i_tcon.h | 4 ++++
    >> >> > 2 files changed, 15 insertions(+)
    >> >> >
    >> >> > diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c
    >> >> > b/drivers/gpu/drm/sun4i/sun4i_tcon.c index 08747fc3ee71..0afb5a94a414
    >> >> > 100644
    >> >> > --- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
    >> >> > +++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
    >> >> > @@ -688,6 +688,16 @@ static int sun4i_tcon_init_clocks(struct device
    >> >> > *dev,
    >> >> >
    >> >> > dev_err(dev, "Couldn't get the TCON bus clock\n");
    >> >> > return PTR_ERR(tcon->clk);
    >> >> >
    >> >> > }
    >> >> >
    >> >> > +
    >> >> > + if (tcon->quirks->has_tcon_top_gate) {
    >> >> > + tcon->top_clk = devm_clk_get(dev, "tcon-top");
    >> >> > + if (IS_ERR(tcon->top_clk)) {
    >> >> > + dev_err(dev, "Couldn't get the TCON TOP bus
    >> >> > clock\n");
    >> >> > + return PTR_ERR(tcon->top_clk);
    >> >> > + }
    >> >> > + clk_prepare_enable(tcon->top_clk);
    >> >> > + }
    >> >> > +
    >> >>
    >> >> Is it required for the TCON itself to operate, or does the TCON
    >> >> requires the TCON TOP, which in turn requires that clock to be
    >> >> functional?
    >> >>
    >> >> I find it quite odd to have a clock that isn't meant for a particular
    >> >> device to actually be wired to another device. I'm not saying this
    >> >> isn't the case, but it would be a first.
    >> >
    >> > Documentation doesn't say much about that gate. I did few tests and TCON
    >> > registers can be read and written even if TCON TOP TV TCON gate is
    >> > disabled. However, there is no image, as expected.
    >>
    >> The R40 manual does include it in the diagram, on page 504. There's also a
    >> mux to select whether the clock comes directly from the CCU or the TV
    >> encoder (a feedback mode?). I assume this is the gate you are referring to
    >> here, in which case it is not a bus clock, but rather the TCON module or
    >> channel clock, strangely routed.
    >>
    >> > More interestingly, I enabled test pattern directly in TCON to eliminate
    >> > influence of the mixer. As soon as I disabled that gate, test pattern on
    >> > HDMI screen was gone, which suggest that this gate influences something
    >> > inside TCON.
    >> >
    >> > Another test I did was that I moved enable/disable gate code to
    >> > sun4i_tcon_channel_set_status() and it worked just as well.
    >> >
    >> > I'll ask AW engineer what that gate actually does, but from what I saw, I
    >> > would say that most appropriate location to enable/disable TCON TOP TV
    >> > TCON
    >> > gate is TCON driver. Alternatively, TCON TOP driver could check if any TV
    >> > TCON is in use and enable appropriate gate. However, that doesn't sound
    >> > right to me for some reason.
    >>
    >> If what I said above it true, then yes, the appropriate location to enable
    >> it is the TCON driver, but moreover, the representation of the clock tree
    >> should be fixed such that the TCON takes the clock from the TCON TOP as its
    >> channel/ module clock instead. That way you don't need this patch, but
    >> you'd add another for all the clock routing.
    >
    > Can you be more specific? I not sure what you mean here.

    For clock related properties in the device tree:

    &tcon_top {
    clocks = <&ccu CLK_BUS_TCON_TOP>,
    <&ccu CLK_TCON_TV0>,
    <&tve0>,
    <&ccu CLK_TCON_TV1>,
    <&tve1>;
    clock-names = "bus", "tcon-tv0", "tve0", "tcon-tv1", "tve1";
    clock-output-names = "tcon-top-tv0", "tcon-top-tv1";
    };

    &tcon_tv0 {
    clocks = <&ccu CLK_BUS_TCON_TV0>, <&tcon_top 0>'
    clock-names = "ahb", "tcon-ch1";
    };

    A diagram would look like:

    | This part is TCON TOP |
    v v
    CCU CLK_TCON_TV0 --|----\ |
    | mux ---- gate ----|-- TCON_TV0
    TVE0 --------------|----/ |

    And the same goes for TCON_TV1 and TVE1.

    The user manual is a bit lacking on how TVE outputs a clock though.

    ChenYu

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