Re: [PATCH v2 04/11] ARM: davinci: da8xx: add usb phy clocks

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On 03/23/2016 11:56 AM, Sekhar Nori wrote:

+static struct clk usb_ref_clk = {
+	.name		= "usb_ref_clk",
+	.rate		= 48000000,
+	.set_rate	= davinci_simple_set_rate,
+};

can we call this usb_refclkin so it matches the TRM name? Also, should
this node be not be coming through individual board files as the rate
depends on what is connected to the usb_refclkin pin? Or is the
expectation that boards will call clk_set_rate() on this clock to the
correct value? If yes, I think it is misleading to populate the .rate here.

You are right. When I did this, I was looking at USB 1.1 only, which MUST be 48MHz. However, this can be used for USB 2.0 which can accept a number of rates.

However, even the main reference oscillator in da850.c has the rate hard coded in da850.c (DA850_REF_FREQ).

The clock initialization will fail if a clock does not have a parent or a rate, so we have to give it a default rate since it is an external clock and has no parent. So, I think 48MHz makes sense for a default value. Most boards will probably not be using this clock anyway, but rather the PLL in the USB 2.0 PHY.


+
+	pr_info("Waiting for USB 2.0 PHY clock good...\n");
+	while (!(readl(DA8XX_SYSCFG0_VIRT(DA8XX_CFGCHIP2_REG))
+						& CFGCHIP2_PHYCLKGD))
+		cpu_relax();

I guess this is copying some earlier code, but still, it will be nice to
see a timeout mechanism here, rather than loop endlessly.

Do you have a suggestion on how to do this?

+
+	/*
+	 * Can't use DA8XX_SYSCFG0_VIRT() here since this can be called before
+	 * da8xx_syscfg0_base is initialized.
+	 */
+	cfgchip2 = ioremap(DA8XX_SYSCFG0_BASE + DA8XX_CFGCHIP2_REG, 4);

Again, not sure if this is juts a theoretical possibility. If yes, I
would rather see you bail out if syscfg0_base is not initialized by the
time you get here than do an ioremap() again.


Will rework clock registration so that this is not necessary.


+
+static struct clk usb20_phy_clk = {
+	.name		= "usb20_phy",
+	.parent		= &pll0_aux_clk,
+	.clk_enable	= usb20_phy_clk_enable,
+	.clk_disable	= usb20_phy_clk_disable,
+	.set_parent	= usb20_phy_clk_set_parent,
+};

I hope you have checked that all boards in mainline use the AUXCLK as
the reference USB 2.0 frequency?


After sending this patch set, I realized that I missed updating existing boards. Will include this in v3.

+
+static struct clk usb11_phy_clk = {
+	.name		= "usb11_phy",
+	.parent		= &usb20_phy_clk,
+	.set_parent	= usb11_phy_clk_set_parent,
+};

Same thing here. I hope all current boards use USB2.0 clk as reference
for USB 1.1 phy


Ditto. Will check on this.


+static void usb20_phy_clk_enable(struct clk *clk)
+{
+	u32 val;
+
+	val = readl(DA8XX_SYSCFG0_VIRT(DA8XX_CFGCHIP2_REG));
+
+	/*
+	 * Turn on the USB 2.0 PHY, but just the PLL, and not OTG. The USB 1.1
+	 * host may use the PLL clock without USB 2.0 OTG being used.
+	 */
+	val &= ~(CFGCHIP2_RESET | CFGCHIP2_PHYPWRDN);
+	val |= CFGCHIP2_PHY_PLLON;
+
+	writel(val, DA8XX_SYSCFG0_VIRT(DA8XX_CFGCHIP2_REG));
+
+	pr_info("Waiting for USB 2.0 PHY clock good...\n");
+	while (!(readl(DA8XX_SYSCFG0_VIRT(DA8XX_CFGCHIP2_REG))
+						& CFGCHIP2_PHYCLKGD))
+		cpu_relax();
+}

Looks like this is pretty much going to be the same code repeated for
DA850 and DA830. So can we move these to a common file like da8xx-usb.c?
You can even register these USB clocks from that file by using
clkdev_add() and clk_register(). This way they can remain to be file local.



I knew someone was going to say that. ;-) Thanks for the suggestion of clkdev_add() and clk_register(), I had not considered that but it sounds like a good idea and will take care of the ioremap problem too.


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