linux-kernel - Re: [linux-sunxi] [PATCH 10/13] [NOT FOR REVIEW NOW] clk: sunxi: Add CLK_SET_RATE

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Date:   Fri, 04 Aug 2017 10:59:03 +0200
From:   Jernej Škrabec <jernej.skrabec@...l.net>
To:     linux-sunxi@...glegroups.com, wens@...e.org
Cc:     Icenowy Zheng <icenowy@...c.io>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>
Subject: Re: [linux-sunxi] [PATCH 10/13] [NOT FOR REVIEW NOW] clk: sunxi: Add CLK_SET_RATE_PARENT flag for H3 HDMI clock

Hi Chen-Yu,

Dne petek, 04. avgust 2017 ob 06:29:50 CEST je Chen-Yu Tsai napisal(a):
> On Fri, Aug 4, 2017 at 12:16 PM, Icenowy Zheng <icenowy@...c.io> wrote:
> > 于 2017年8月4日 GMT+08:00 下午12:15:27, Chen-Yu Tsai <wens@...e.org> 写到:
> >>Hi,
> >>
> >>On Tue, Aug 1, 2017 at 9:13 PM, Icenowy Zheng <icenowy@...c.io> wrote:
> >>> From: Jernej Skrabec <jernej.skrabec@...l.net>
> >>> 
> >>> When setting the HDMI clock of H3, the PLL_VIDEO clock needs to be
> >>
> >>set.
> >>
> >>> Add CLK_SET_RATE_PARENT flag for H3 HDMI clock.
> >>> 
> >>> Signed-off-by: Jernej Skrabec <jernej.skrabec@...l.net>
> >>> Signed-off-by: Icenowy Zheng <icenowy@...c.io>
> >>> ---
> >>> 
> >>>  drivers/clk/sunxi-ng/ccu-sun8i-h3.c | 2 +-
> >>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>> 
> >>> diff --git a/drivers/clk/sunxi-ng/ccu-sun8i-h3.c
> >>
> >>b/drivers/clk/sunxi-ng/ccu-sun8i-h3.c
> >>
> >>> index b1127e8629d9..2ebb3d865b01 100644
> >>> --- a/drivers/clk/sunxi-ng/ccu-sun8i-h3.c
> >>> +++ b/drivers/clk/sunxi-ng/ccu-sun8i-h3.c
> >>> @@ -474,7 +474,7 @@ static SUNXI_CCU_GATE(avs_clk,
> >>
> >>"avs",          "osc24M",
> >>
> >>>  static const char * const hdmi_parents[] = { "pll-video" };
> >>>  static SUNXI_CCU_M_WITH_MUX_GATE(hdmi_clk, "hdmi", hdmi_parents,
> >>> 
> >>> -                                0x150, 0, 4, 24, 2, BIT(31), 0);
> >>> +                                0x150, 0, 4, 24, 2, BIT(31),
> >>
> >>CLK_SET_RATE_PARENT);
> >>
> >>Line is longer than 80 characters.
> >>
> >>This looks independent enough so I've merged this for 4.14 with the
> >>offending line wrapped and the following tag added:
> >>
> >>Fixes: 0577e4853bfb ("clk: sunxi-ng: Add H3 clocks")
> >>
> > Please don't merge this now until Jernej send it.
> 
> (Dropped Rob, devicetree and dri mailing lists)
> 
> Hi Jernej,
> 
> Is it OK if we take this patch for the next release? Or rather,
> if there anything blocking this patch?

I just made last check now and this patch is indeed OK. Before merging, please 
read explanation below.

Background:
According to H3 datasheet and BSP driver, HDMI clock has M factor (divider) to 
correctly set pixel clock to desired value. However, Jens Kuske discovered 
that this factor doesn't play any role whatsoever and instead, division factor 
set in PHY registers is the important one. I confirmed that on BSP kernel by 
tying M factor to 0. Both, HDMI video and audio, still worked correctly.

So that flag is necessary to set pll-video to pixel clock * div factor. I can 
also change HDMI clock type to SUNXI_CCU_GATE (without M factor) and document 
discrepancy with datasheet in ccu-sun8i-h3.c. Alternatively to this patch, 
just in case, to be on the safe side, I can add pll-video clock phandle to the 
dt node. However, as far as I know, that might prevent selecting another 
parent on SoCs where HDMI clock has multiple parents.

Regards,
Jernej

> 
> Thanks
> ChenYu
> 
> >>ChenYu
> >>
> >>>  static SUNXI_CCU_GATE(hdmi_ddc_clk,    "hdmi-ddc",     "osc24M",
> >>>  
> >>>                       0x154, BIT(31), 0);
> >>> 
> >>> --
> >>> 2.13.0
> >>> 
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