Subject: [PATCH v4 3/3] ARM: imx6: Fix procedure to switch the parent of LDB_DI_CLK

From: [email-masked] (Akshay Bhat)
Date: Tue, 1 Mar 2016 16:41:36 -0500

Hi Philipp,

On 02/26/2016 03:51 AM, Philipp Zabel wrote:
> From: Fabio Estevam <[email-masked]>
>

<snip>

> +static void init_ldb_clks(struct device_node *np, void __iomem *ccm_base)
> +{
> +	unsigned int reg;
> +	unsigned int sel[2][4];
> +	int i;
> +
> +	reg = readl_relaxed(ccm_base + CCM_CS2CDR);
> +	sel[0][0] = (reg >> CS2CDR_LDB_DI0_CLK_SEL_SHIFT) & 7;
> +	sel[1][0] = (reg >> CS2CDR_LDB_DI1_CLK_SEL_SHIFT) & 7;
> +
> +	sel[0][3] = sel[0][2] = sel[0][1] = sel[0][0];
> +	sel[1][3] = sel[1][2] = sel[1][1] = sel[1][0];
> +
> +	of_assigned_ldb_sels(np, &sel[0][3], &sel[1][3]);
> +
> +	for (i = 0; i < 2; i++) {
> +		/* Warn if a glitch might have been introduced already */
> +		if (sel[i][0] != 3) {
> +			pr_warn("ccm: ldb_di%d_sel already changed from reset value: %d\n",
> +				i, sel[i][0]);
> +		}
> +
> +		if (sel[i][0] == sel[i][3])
> +			continue;
> +
> +		/* Only switch to or from pll2_pfd2_396m if it is disabled */
> +		if ((sel[i][0] == 2 || sel[i][3] == 2) &&
> +		    (clk_get_parent(clk[IMX6QDL_CLK_PERIPH_PRE]) ==
> +		     clk[IMX6QDL_CLK_PLL2_PFD2_396M])) {
> +			pr_err("ccm: ldb_di%d_sel: couldn't disable pll2_pfd2_396m\n",
> +			       i);
> +			sel[i][3] = sel[i][2] = sel[i][1] = sel[i][0];
> +			continue;
> +		}
> +
> +		/*
> +		 * It is unclear whether the procedure works for switching from
> +		 * pll3_usb_otg to any other parent than pll5_video_div
> +		 */
> +		if (sel[i][0] > 3 && sel[i][0] != (sel[i][3] | 4)) {
> +			pr_err("ccm: ldb_di%d_sel workaround only for top mux\n",
> +			       i);
> +			sel[i][3] = sel[i][2] = sel[i][1] = sel[i][0];
> +			continue;
> +		}

EB821 doesn't mention the above restriction. My understanding was as 
long as the clock source you are switching from/to is disabled it should 
be ok to do so. Maybe someone from Freescale can comment?

> +
> +		/* First switch to the bottom mux */
> +		sel[i][1] = sel[i][0] | 4;
> +

Not sure if this really matters but as per EB821 Section 4.2, 6 b, the 
recommended setting for sel[i][1] is 7

> +		/* Then configure the top mux before switching back to it */
> +		sel[i][2] = sel[i][3] | 4;
> +

Same goes here, as per EB821, Section 4.2, 6 c, the recommended setting 
for sel[i][2] is 4

Thanks,
Akshay