Re: [PATCH v8 09/24] drm/rockchip: dw_hdmi: Add support for niu clk

From: Sascha Hauer <s.hauer@pengutronix.de>
To: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Cc: "elaine.zhang" <zhangqing@rock-chips.com>,
	Robin Murphy <robin.murphy@arm.com>,
	devicetree@vger.kernel.org,
	Benjamin Gaignard <benjamin.gaignard@collabora.com>,
	Peter Geis <pgwipeout@gmail.com>,
	Sandy Huang <hjc@rock-chips.com>,
	linux-rockchip@lists.infradead.org,
	Michael Riesch <michael.riesch@wolfvision.net>,
	kernel@pengutronix.de, Andy Yan <andy.yan@rock-chips.com>,
	linux-arm-kernel@lists.infradead.org,
	dri-devel@lists.freedesktop.org
Subject: Re: [PATCH v8 09/24] drm/rockchip: dw_hdmi: Add support for niu clk
Date: Mon, 14 Mar 2022 09:18:35 +0100	[thread overview]
Message-ID: <20220314081834.GK405@pengutronix.de> (raw)
In-Reply-To: <4712e128-8a14-e361-0819-911dc3453372@collabora.com>

On Sun, Mar 13, 2022 at 12:07:56AM +0300, Dmitry Osipenko wrote:
> On 3/11/22 11:33, Sascha Hauer wrote:
> > The rk3568 HDMI has an additional clock that needs to be enabled for the
> > HDMI controller to work. This clock is not needed for the HDMI
> > controller itself, but to make the SoC internal bus logic work. From the
> > reference manual:
> > 
> >> 2.8.6 NIU Clock gating reliance
> >>
> >> A part of niu clocks have a dependence on another niu clock in order to
> >> sharing the internal bus. When these clocks are in use, another niu
> >> clock must be opened, and cannot be gated.  These clocks and the special
> >> clock on which they are relied are as following:
> >>
> >> Clocks which have dependency     The clock which can not be gated
> >> -----------------------------------------------------------------
> >> ...
> >> pclk_vo_niu, hclk_vo_s_niu       hclk_vo_niu
> >> ...
> > The clock framework does not support turning on a clock whenever another
> > clock is turned on, so this patch adds support for the dependent clock
> > to the HDMI driver. We call it "NIU", which is for "Native Interface
> > Unit"
> 
> This still doesn't make sense to me. You're saying that "pclk_vo_niu,
> hclk_vo_s_niu" depend on "hclk_vo_niu", but HDMI doesn't use pclk_vo, it
> uses pclk_hdmi.

pclk_hdmi_host is a child clock of pclk_vo:

     aclk_vo                  2        2        0   300000000          0     0  50000         Y
        aclk_hdcp             0        0        0   300000000          0     0  50000         N
        pclk_vo               2        3        0    75000000          0     0  50000         Y
           pclk_edp_ctrl      0        0        0    75000000          0     0  50000         N
           pclk_dsitx_1       0        0        0    75000000          0     0  50000         N
           pclk_dsitx_0       1        2        0    75000000          0     0  50000         Y
           pclk_hdmi_host     1        2        0    75000000          0     0  50000         Y
           pclk_hdcp          0        0        0    75000000          0     0  50000         N
        hclk_vo               2        5        0   150000000          0     0  50000         Y
           hclk_hdcp          0        0        0   150000000          0     0  50000         N
           hclk_vop           0        2        0   150000000          0     0  50000         N

Sascha

> I don't see how these "niu" clocks are related to HDMI
> from your description. The pclk_vo should remain being disabled for HDMI.
> 
> I already said before that the datasheet suggests that hclk_vo needs to
> be enabled in order to ungate the AHB part of the VO module, which is
> needed for CPU accesses. Elain, could you please confirm this or clarify
> more about why hclk_vo needs to be enabled for HDMI?
> 

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