Am Donnerstag, den 07.03.2019, 12:56 +0000 schrieb Anson Huang:

Hi, Lucas

Best Regards!
Anson Huang

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-----Original Message-----

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From: Lucas Stach [mailto:l.stach@pengutronix.de]

Sent: 2019年3月7日 20:06

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To: Anson Huang <redacted>; shawnguo@kernel.org;

s.hauer@pengutronix.de; kernel@pengutronix.de; Fabio Estevam

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[off-list ref]; robh+dt@kernel.org; mark.rutland@arm.com;

mturquette@baylibre.com; sboyd@kernel.org; Abel Vesa

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[off-list ref]; agx@sigxcpu.org; linux-arm-

kernel@lists.infradead.org; devicetree@vger.kernel.org; linux-

kernel@vger.kernel.org; linux-clk@vger.kernel.org

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Cc: dl-linux-imx <redacted>

Subject: Re: [PATCH 2/3] clk: imx8mq: add hdmi_phy_27m clock as pll's
reference clock

Am Donnerstag, den 07.03.2019, 03:41 +0000 schrieb Anson Huang:

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There is another 27MHz OSC inside i.MX8MQ's display block and it can
be one of reference clocks of all PLLs, add it into clock tree and
also add it as PLL's reference clock.

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Signed-off-by: Anson Huang <redacted>

---
 drivers/clk/imx/clk-imx8mq.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/clk/imx/clk-imx8mq.c

b/drivers/clk/imx/clk-imx8mq.c index a9b3888..bb1bf9b 100644

--- a/drivers/clk/imx/clk-imx8mq.c
+++ b/drivers/clk/imx/clk-imx8mq.c

@@ -26,7 +26,7 @@ static u32 share_count_nand;

 static struct clk *clks[IMX8MQ_CLK_END];

-static const char * const pll_ref_sels[] = { "osc_25m", "osc_27m",
"dummy", "dummy", };
+static const char * const pll_ref_sels[] = { "osc_25m", "osc_27m",
+"osc_hdmi_phy_27m", "dummy", };
 static const char * const arm_pll_bypass_sels[] = {"arm_pll",
"arm_pll_ref_sel", };
 static const char * const gpu_pll_bypass_sels[] = {"gpu_pll",
"gpu_pll_ref_sel", };
 static const char * const vpu_pll_bypass_sels[] = {"vpu_pll",
"vpu_pll_ref_sel", }; @@ -281,6 +281,7 @@ static int

imx8mq_clocks_probe(struct platform_device *pdev)

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 	clks[IMX8MQ_CLK_32K] = of_clk_get_by_name(np, "ckil");
 	clks[IMX8MQ_CLK_25M] = of_clk_get_by_name(np, "osc_25m");
 	clks[IMX8MQ_CLK_27M] = of_clk_get_by_name(np, "osc_27m");
+	clks[IMX8MQ_CLK_HDMI_PHY_27M] = of_clk_get_by_name(np,

+"osc_hdmi_phy_27m");

This is not acceptable. This adds a new required clock input, without
bothering to add the corresponding binding information or thinking about
backwards compatibility. At this point there are existing DTs out there, which
don't provide this required clock, which will cause a full boot regression. This
can only be an optional clock input at this point.

What do you think if we don't get such clock from DT? Just register this fixed clock
in clock driver directly, then there will be no dependency of DT.

I don't think that's a good idea, as there can probably be use-cases
where having the XTAL unpopulated is actually a valid system
configuration, so not having this clock must be valid for the CCM
driver.

Regards,
Lucas

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