usb: dwc3: qcom: Add delays in UTMI clock selection for Qscratch

Added delays before and after setting the PIPE_UTMI_CLK_SEL and
PIPE3_PHYSTATUS_SW bits in the Qscratch GENERAL_CFG register
during UTMI clock selection for DWC3 on Qualcomm platforms.

These delays help ensure proper timing and stability of the UTMI
clock switching sequence, potentially avoiding race conditions or
unstable PHY behavior during initialization.

Tested on platforms using Qscratch-based DWC3 PHY configuration.

This change is taken from this Linux kernel implementation:
https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/usb/dwc3/dwc3-qcom.c?id=a4333c3a6ba9ca9cff50a3c1d1bf193dc5489e1c

Signed-off-by: Balaji Selvanathan <balaji.selvanathan@oss.qualcomm.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@kernel.org>
Link: https://patch.msgid.link/20250627045244.2225303-1-balaji.selvanathan@oss.qualcomm.com
Signed-off-by: Casey Connolly <casey.connolly@linaro.org>

diff --git a/drivers/usb/dwc3/dwc3-generic.c b/drivers/usb/dwc3/dwc3-generic.c
index bb11613a58759f122228b0b511c5b4c7cf99df73..02c02b1d80e4f5299c285268e4af6bf97c4c8e0f 100644 (file)
--- a/drivers/usb/dwc3/dwc3-generic.c
+++ b/drivers/usb/dwc3/dwc3-generic.c
@@ -461,9 +461,13 @@ static void dwc3_qcom_select_utmi_clk(void __iomem *qscratch_base)
        setbits_le32(qscratch_base + QSCRATCH_GENERAL_CFG,
                          PIPE_UTMI_CLK_DIS);
 
+       udelay(100);
+
        setbits_le32(qscratch_base + QSCRATCH_GENERAL_CFG,
                          PIPE_UTMI_CLK_SEL | PIPE3_PHYSTATUS_SW);
 
+       udelay(100);
+
        clrbits_le32(qscratch_base + QSCRATCH_GENERAL_CFG,
                          PIPE_UTMI_CLK_DIS);
 }