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

[Robin Murphy <robin.murphy@arm.com>]

On 2022-02-25 13:11, 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>;
>          };
> 
> The HDMI controller is part of that domain, so I think this should work,
> but it doesn't. That's where I am now, I'll have a closer look.

Ah, interesting. Looking at the clock driver, I'd also be suspicious 
whether pclk_vo is somehow messed up such that we're currently relying 
on hclk_vo to keep the common grandparent enabled. Seems like the DSI 
and eDP (and HDCP if anyone ever used it) registers would be similarly 
affected if so, and sure enough they both have a similarly suspect extra 
"hclk" in the downstream DT too.

Robin.

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