Hi Robert,
On 1/13/22 11:42 PM, Robert Hancock wrote:
Previously a device tree property was added to allow overriding the
reference clock period parameter if the default value used was incorrect.
However, there is another register field, GFLADJ_REFCLK_FLADJ, which
reflects the fractional nanosecond portion of the reference clock
period. Add a snps,ref-clock-fladj property to allow configuring this
as well.
On the Xilinx ZynqMP platform, the reference clock appears to always
be 20 MHz, giving a clock period of 50 ns. However, the default value
of GFLADJ_REFCLK_FLADJ was 1008 rather than 0 as it should have been,
which prevented many USB devices from functioning properly. The
psu_init code run by the Xilinx first-stage boot loader sets this
value to 0, however when the controller is reset by the dwc3-xilinx
layer, the incorrect default value is restored. This configuration
property allows ensuring that the correct value is always used.
Reviewed-by: Thinh Nguyen <Thinh.Nguyen@xxxxxxxxxxxx>
Signed-off-by: Robert Hancock <robert.hancock@xxxxxxxxxx>
---
drivers/usb/dwc3/core.c | 35 +++++++++++++++++++++++++++++++++++
drivers/usb/dwc3/core.h | 5 +++++
2 files changed, 40 insertions(+)
diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index f4c09951b517..ad224fb8088e 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -359,6 +359,37 @@ static void dwc3_ref_clk_period(struct dwc3 *dwc)
}
+/**
+ * dwc3_ref_clk_fladj - Reference clock period adjustment configuration
+ * @dwc: Pointer to our controller context structure
+ *
+ * GFLADJ_REFCLK_FLADJ should be set based on the fractional portion of the
+ * reference clock period, where the integer portion is set in GUCTL_REFCLKPER.
+ * Calculated as: ((125000/ref_clk_period_integer)-(125000/ref_clk_period)) * ref_clk_period
+ * where ref_clk_period_integer is the period specified in GUCTL_REFCLKPER and
+ * ref_clk_period is the period including fractional value.
+ * This value can be specified in the device tree if the default value is incorrect.
+ * Note that 0 is a valid value.
+ */
+static void dwc3_ref_clk_fladj(struct dwc3 *dwc)
+{
+ u32 reg;
+ u32 reg_new;
+
+ if (DWC3_VER_IS_PRIOR(DWC3, 250A))
+ return;
+
+ if (!dwc->ref_clk_fladj_set)
+ return;
+
+ reg = dwc3_readl(dwc->regs, DWC3_GFLADJ);
+ reg_new = reg & ~DWC3_GFLADJ_REFCLK_FLADJ_MASK;
+ reg_new |= FIELD_PREP(DWC3_GFLADJ_REFCLK_FLADJ_MASK, dwc->ref_clk_fladj);
+ if (reg_new != reg)
+ dwc3_writel(dwc->regs, DWC3_GFLADJ, reg_new);
+}
+
+
/**
* dwc3_free_one_event_buffer - Frees one event buffer
* @dwc: Pointer to our controller context structure
@@ -1033,6 +1064,7 @@ static int dwc3_core_init(struct dwc3 *dwc)
/* Adjust Reference Clock Period */
dwc3_ref_clk_period(dwc);
+ dwc3_ref_clk_fladj(dwc);
dwc3_set_incr_burst_type(dwc);
@@ -1418,6 +1450,9 @@ static void dwc3_get_properties(struct dwc3 *dwc)
&dwc->fladj);
device_property_read_u32(dev, "snps,ref-clock-period-ns",
&dwc->ref_clk_per);
+ if (!device_property_read_u32(dev, "snps,ref-clock-fladj",
+ &dwc->ref_clk_fladj))
+ dwc->ref_clk_fladj_set = true;
dwc->dis_metastability_quirk = device_property_read_bool(dev,
"snps,dis_metastability_quirk");
diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
index e1cc3f7398fb..5011296786de 100644
--- a/drivers/usb/dwc3/core.h
+++ b/drivers/usb/dwc3/core.h
@@ -388,6 +388,7 @@
/* Global Frame Length Adjustment Register */
#define DWC3_GFLADJ_30MHZ_SDBND_SEL BIT(7)
#define DWC3_GFLADJ_30MHZ_MASK 0x3f
+#define DWC3_GFLADJ_REFCLK_FLADJ_MASK 0x3fff00
/* Global User Control Register*/
#define DWC3_GUCTL_REFCLKPER_MASK 0xffc00000
@@ -985,6 +986,8 @@ struct dwc3_scratchpad_array {
* @regs_size: address space size
* @fladj: frame length adjustment
* @ref_clk_per: reference clock period configuration
+ * @ref_clk_fladj_set: whether ref_clk_fladj value is set/valid
+ * @ref_clk_fladj: reference clock period fractional adjustment
* @irq_gadget: peripheral controller's IRQ number
* @otg_irq: IRQ number for OTG IRQs
* @current_otg_role: current role of operation while using the OTG block
@@ -1166,6 +1169,8 @@ struct dwc3 {
u32 fladj;
u32 ref_clk_per;
+ bool ref_clk_fladj_set;
+ u32 ref_clk_fladj;
u32 irq_gadget;
u32 otg_irq;
u32 current_otg_role;
Doesn't this property already exist as snps,quirk-frame-length-adjustment?
---
I realize the cat is already out of the bag, but this seems like
something which could be better modeled with a frequency property, or by
using a clock. With these bindings, the board maintainer has to
determine the reference clock frequency and then manually calculate the
fractional adjustment. If the reference clock is ever changed (e.g. in
a new board revision), the maintainer must then update two properties.
However, Linux could calculate all this automatically.
We already have a clock input for the reference with which we can
determine the frequency (according to bindings/usb/snps,dwc3.yaml,
though I cannot see where it is implemented in the driver). Even on
platforms without a reference clock (such as USB over PCIe [1]), one can
just add a fixed-rate clock to act as the reference.
--Sean
[1] https://lore.kernel.org/all/9f399bdf1ff752e31ab7497e3d5ce19bbb3ff247.1630389452.git.baruch@xxxxxxxxxx/
