Re: [PATCH v7 10/24] drm/rockchip: dw_hdmi: Add support for hclk

[Sascha Hauer <s.hauer@pengutronix.de>]

On Wed, Mar 02, 2022 at 12:25:28PM +0100, Sascha Hauer wrote:
> On Tue, Mar 01, 2022 at 01:39:31PM +0000, Robin Murphy wrote:
> > On 2022-02-28 14:19, Sascha Hauer wrote:
> > > On Fri, Feb 25, 2022 at 02:11:54PM +0100, Sascha Hauer wrote:
> > > > On Fri, Feb 25, 2022 at 12:41:23PM +0000, Robin Murphy wrote:
> > > > > On 2022-02-25 11:10, Dmitry Osipenko wrote:
> > > > > > 25.02.2022 13:49, Sascha Hauer пишет:
> > > > > > > On Fri, Feb 25, 2022 at 01:26:14PM +0300, Dmitry Osipenko wrote:
> > > > > > > > 25.02.2022 10:51, Sascha Hauer пишет:
> > > > > > > > > The rk3568 HDMI has an additional clock that needs to be enabled for the
> > > > > > > > > HDMI controller to work. The purpose of that clock is not clear. It is
> > > > > > > > > named "hclk" in the downstream driver, so use the same name.
> > > > > > > > > 
> > > > > > > > > Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
> > > > > > > > > ---
> > > > > > > > > 
> > > > > > > > > Notes:
> > > > > > > > >       Changes since v5:
> > > > > > > > >       - Use devm_clk_get_optional rather than devm_clk_get
> > > > > > > > > 
> > > > > > > > >    drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c | 16 ++++++++++++++++
> > > > > > > > >    1 file changed, 16 insertions(+)
> > > > > > > > > 
> > > > > > > > > diff --git a/drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c b/drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c
> > > > > > > > > index fe4f9556239ac..c6c00e8779ab5 100644
> > > > > > > > > --- a/drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c
> > > > > > > > > +++ b/drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c
> > > > > > > > > @@ -76,6 +76,7 @@ struct rockchip_hdmi {
> > > > > > > > >    	const struct rockchip_hdmi_chip_data *chip_data;
> > > > > > > > >    	struct clk *ref_clk;
> > > > > > > > >    	struct clk *grf_clk;
> > > > > > > > > +	struct clk *hclk_clk;
> > > > > > > > >    	struct dw_hdmi *hdmi;
> > > > > > > > >    	struct regulator *avdd_0v9;
> > > > > > > > >    	struct regulator *avdd_1v8;
> > > > > > > > > @@ -229,6 +230,14 @@ static int rockchip_hdmi_parse_dt(struct rockchip_hdmi *hdmi)
> > > > > > > > >    		return PTR_ERR(hdmi->grf_clk);
> > > > > > > > >    	}
> > > > > > > > > +	hdmi->hclk_clk = devm_clk_get_optional(hdmi->dev, "hclk");
> > > > > > > > > +	if (PTR_ERR(hdmi->hclk_clk) == -EPROBE_DEFER) {
> > > > > > > > 
> > > > > > > > Have you tried to investigate the hclk? I'm still thinking that's not
> > > > > > > > only HDMI that needs this clock and then the hardware description
> > > > > > > > doesn't look correct.
> > > > > > > 
> > > > > > > I am still not sure what you mean. Yes, it's not only the HDMI that
> > > > > > > needs this clock. The VOP2 needs it as well and the driver handles that.
> > > > > > 
> > > > > > I'm curious whether DSI/DP also need that clock to be enabled. If they
> > > > > > do, then you aren't modeling h/w properly AFAICS.
> > > > > 
> > > > > Assuming nobody at Rockchip decided to make things needlessly inconsistent
> > > > > with previous SoCs, HCLK_VOP should be the clock for the VOP's AHB slave
> > > > > interface. Usually, if that affected anything other than accessing VOP
> > > > > registers, indeed it would smell of something being wrong in the clock tree,
> > > > > but in this case I'd also be suspicious of whether it might have ended up
> > > > > clocking related GRF registers as well (either directly, or indirectly via
> > > > > some gate that the clock driver hasn't modelled yet).
> > > > 
> > > > Ok, I am beginning to understand. I verified that hdmi, mipi and dp are
> > > > hanging when HCLK_VOP is disabled by disabling that clock via sysfs
> > > > using CLOCK_ALLOW_WRITE_DEBUGFS. When it's disabled then the registers
> > > > of that units can't be accessed. However, when I disable HCLK_VOP by
> > > > directly writing to the gate bit RK3568_CLKGATE_CON(20) then only
> > > > accessing VOP registers hangs, the other units stay functional.
> > > > So it seems it must be the parent clock which must be enabled. The
> > > > parent clock is hclk_vo. This clock should be handled as part of the
> > > > RK3568_PD_VO power domain:
> > > > 
> > > > 	power-domain@RK3568_PD_VO {
> > > >                  reg = <RK3568_PD_VO>;
> > > >                  clocks = <&cru HCLK_VO>,
> > > >                           <&cru PCLK_VO>,
> > > >                           <&cru ACLK_VOP_PRE>;
> > > >                   pm_qos = <&qos_hdcp>,
> > > >                            <&qos_vop_m0>,
> > > >                            <&qos_vop_m1>;
> > > >                   #power-domain-cells = <0>;
> > > >          };
> > > 
> > > Forget this. The clocks in this node are only enabled during enabling or
> > > disabling the power domain, they are disabled again immediately afterwards.
> > > 
> > > OK, I need HCLK_VO to access the HDMI registers. I verified that by
> > > disabling HCLK_VO at register level (CRU_GATE_CON(20) BIT(1)). The
> > > HDMI registers become inaccessible then. This means I'll replace
> > > HCLK_VOP in the HDMI node with HCLK_VO. Does this sound sane?
> > 
> > Well, it's still a mystery hack overall, and in some ways it seems even more
> > suspect to be claiming a whole branch of the clock tree rather than a leaf
> > gate with a specific purpose. I'm really starting to think that the
> > underlying issue here is a bug in the clock driver, or a hardware mishap
> > that should logically be worked around by the clock driver, rather than
> > individual the consumers.
> > 
> > Does it work if you hack the clock driver to think that PCLK_VO is a child
> > of HCLK_VO? Even if that's not technically true, it would seem to
> > effectively match the observed behaviour (i.e. all 3 things whose register
> > access apparently *should* be enabled by a gate off PCLK_VO, seem to also
> > require HCLK_VO).
> 
> Yes, that works as expected. I am not sure though if we really want to
> go that path. The pclk rates will become completely bogus with this and
> should we have to play with the rates in the future we might regret this
> step.

How do we proceed here? I can include a patch which makes PCLK_VO a
child of HCLK_VO if that's what we agree upon.

Sascha

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