[rtc-linux] Re: [PATCH] rtc: sunxi: use external oscillator
From: Maxime Ripard <hidden>
Date: 2016-07-06 20:20:01
On Wed, Jul 06, 2016 at 10:43:00AM +0200, Stephan Roslen wrote:
We noticed some serious drift problems in Allwinner A20 RTCs. I found out, that the oscillator source needs to be set to an external 32.768 KHz oscillator instead of the internal 32.000 KHz oscillator.
You should wrap the commit description.
quoted hunk ↗ jump to hunk
Signed-off-by: Stephan Roslen <redacted> --- drivers/rtc/rtc-sunxi.c | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+)diff --git a/drivers/rtc/rtc-sunxi.c b/drivers/rtc/rtc-sunxi.c index abada60..001256e 100644 --- a/drivers/rtc/rtc-sunxi.c +++ b/drivers/rtc/rtc-sunxi.c@@ -34,9 +34,19 @@ #include <linux/types.h> #define SUNXI_LOSC_CTRL 0x0000 + +/* magic number required to set bit 0 */ +#define SUNXI_LOSC_CTRL_KEY 0x16AA0000 + +#define SUNXI_LOSC_CTRL_AUTO_SWT_EN BIT(14) + #define SUNXI_LOSC_CTRL_RTC_HMS_ACC BIT(8) #define SUNXI_LOSC_CTRL_RTC_YMD_ACC BIT(7) +#define SUNXI_LOSC_CTRL_EXT_GSM1 BIT(3) +#define SUNXI_LOSC_CTRL_EXT_GSM0 BIT(2) +#define SUNXI_LOSC_CTRL_SRC_SEL BIT(0) + #define SUNXI_RTC_YMD 0x0004 #define SUNXI_RTC_HMS 0x0008@@ -438,6 +448,8 @@ static int sunxi_rtc_probe(struct platform_device *pdev) struct resource *res; int ret; + uint32_t loscctrl; + chip = devm_kzalloc(&pdev->dev, sizeof(*chip), GFP_KERNEL); if (!chip) return -ENOMEM;@@ -468,6 +480,19 @@ static int sunxi_rtc_probe(struct platform_device *pdev) return -ENODEV; } + loscctrl = readl(chip->base + SUNXI_LOSC_CTRL); + loscctrl &= ~(SUNXI_LOSC_CTRL_AUTO_SWT_EN); + loscctrl |= (SUNXI_LOSC_CTRL_SRC_SEL | SUNXI_LOSC_CTRL_KEY); + loscctrl |= SUNXI_LOSC_CTRL_EXT_GSM1; + writel(loscctrl, chip->base + SUNXI_LOSC_CTRL); + udelay(100);
Why is that udelay needed?
+
+ loscctrl = readl(chip->base + SUNXI_LOSC_CTRL);
+ if (!(loscctrl & SUNXI_LOSC_CTRL_SRC_SEL)) {
+ dev_err(&pdev->dev, "Error: Set LOSC to external failed.\n");
+ dev_err(&pdev->dev, "Warning: RTC time will be wrong!\n");
+ }
+This isn't needed The issue is actually worse than that. That register controls the losc source for the whole clock tree, so it will affect every clock in the system. In order to have that correctly propagated, you should register a new mux here in the clock framework, and have all the other clocks using that mux as a parent. That's going to be tricky, because the clocks usually probe way earlier than the RTC driver. So I'm guessing you could do a clock driver that maps the registers, register its clock, and then when the RTC probes just takes over what has been setup already by the clock driver. This also means removing the ability for the RTC to be compiled as a module. Maxime -- Maxime Ripard, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com -- You received this message because you are subscribed to "rtc-linux". Membership options at http://groups.google.com/group/rtc-linux . Please read http://groups.google.com/group/rtc-linux/web/checklist before submitting a driver. --- You received this message because you are subscribed to the Google Groups "rtc-linux" group. To unsubscribe from this group and stop receiving emails from it, send an email to rtc-linux+unsubscribe@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
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