linux-kernel - [RFC] clk: imx: Let IMX8MN_CLK_DISP

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Date:   Mon, 13 Mar 2023 21:44:49 -0500
From:   Adam Ford <aford173@...il.com>
To:     linux-clk@...r.kernel.org
Cc:     peng.fan@....com, l.stach@...gutronix.de,
        Adam Ford <aford173@...il.com>,
        Abel Vesa <abelvesa@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [RFC] clk: imx: Let IMX8MN_CLK_DISP_PIXEL set parent rate

By default the display pixel clock needs to be evenly divide
down from 594MHz which rules out a significant number of
resolution and refresh rates.
The current clock tree looks something like:

 video_pll                594000000
  video_pll_bypass        594000000
   video_pll_out          594000000
    disp_pixel            148500000
     disp_pixel_clk       148500000

To enable CLK_SET_RATE_PARENT on disp_pixel, a helper function
needs to be added called imx8m_clk_hw_composite_flags which
can pass the additional flag to the clock controller. Letting
disp_pixel set video_pll_out rate should actually lower the
clock rates of video_pll_bypass and video_pll as well, since
those clocks are already configured to enable CLK_SET_RATE_PARENT.

Signed-off-by: Adam Ford <aford173@...il.com>
---

This is an RFC, because even with this patch, the video_pll_out clock
does not drop to 148500000 like I would expect.  The video_pll clock
is a fractional pll, so it should be able to generate a significant
number of optional clock frequencies to facilitate video.

diff --git a/drivers/clk/imx/clk-imx8mn.c b/drivers/clk/imx/clk-imx8mn.c
index af256ade554f..a116cc40d7d0 100644
--- a/drivers/clk/imx/clk-imx8mn.c
+++ b/drivers/clk/imx/clk-imx8mn.c
@@ -470,7 +470,7 @@ static int imx8mn_clocks_probe(struct platform_device *pdev)
 	hws[IMX8MN_CLK_DRAM_ALT] = imx8m_clk_hw_fw_managed_composite("dram_alt", imx8mn_dram_alt_sels, base + 0xa000);
 	hws[IMX8MN_CLK_DRAM_APB] = imx8m_clk_hw_fw_managed_composite_critical("dram_apb", imx8mn_dram_apb_sels, base + 0xa080);
 
-	hws[IMX8MN_CLK_DISP_PIXEL] = imx8m_clk_hw_composite("disp_pixel", imx8mn_disp_pixel_sels, base + 0xa500);
+	hws[IMX8MN_CLK_DISP_PIXEL] = imx8m_clk_hw_composite_flags("disp_pixel", imx8mn_disp_pixel_sels, base + 0xa500, CLK_SET_RATE_PARENT);
 	hws[IMX8MN_CLK_SAI2] = imx8m_clk_hw_composite("sai2", imx8mn_sai2_sels, base + 0xa600);
 	hws[IMX8MN_CLK_SAI3] = imx8m_clk_hw_composite("sai3", imx8mn_sai3_sels, base + 0xa680);
 	hws[IMX8MN_CLK_SAI5] = imx8m_clk_hw_composite("sai5", imx8mn_sai5_sels, base + 0xa780);
diff --git a/drivers/clk/imx/clk.h b/drivers/clk/imx/clk.h
index 689b3ad927c0..9977b512845b 100644
--- a/drivers/clk/imx/clk.h
+++ b/drivers/clk/imx/clk.h
@@ -414,6 +414,10 @@ struct clk_hw *__imx8m_clk_hw_composite(const char *name,
 	_imx8m_clk_hw_composite(name, parent_names, reg, \
 			0, IMX_COMPOSITE_CLK_FLAGS_DEFAULT)
 
+#define imx8m_clk_hw_composite_flags(name, parent_names, reg, flags) \
+	_imx8m_clk_hw_composite(name, parent_names, reg, \
+			0, IMX_COMPOSITE_CLK_FLAGS_DEFAULT |  flags)
+
 #define imx8m_clk_hw_composite_critical(name, parent_names, reg) \
 	_imx8m_clk_hw_composite(name, parent_names, reg, \
 			0, IMX_COMPOSITE_CLK_FLAGS_CRITICAL)
-- 
2.37.2