[PATCH] usb: dwc2: wa for isoc packet tx fifo flush at periodic frame boundary

[PATCH] usb: dwc2: wa for isoc packet tx fifo flush at periodic frame boundary

[Fabrice Gasnier]

If an isochronous packet is still being transmitted, when the end of
periodic frame interval elapses, using dma desc on dwc2 controller,
the device wrongly flushes the pending packets from the tx fifo.
This can lead to a huge packet is sent on the bus, leading to the host
finally reset the bus, and re-enumerate it.

Workaround it by tuning the periodic frame interval limit from 80% to 95%,
on the affected cores (2.70a to 4.00a). It makes the issue very unlikely
to occur.

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
---
 drivers/usb/dwc2/core.h   |  1 +
 drivers/usb/dwc2/gadget.c | 13 +++++++++++++
 2 files changed, 14 insertions(+)

diff --git a/drivers/usb/dwc2/core.h b/drivers/usb/dwc2/core.h
index 767251aa1aa3..3bce41b4dfa6 100644
--- a/drivers/usb/dwc2/core.h
+++ b/drivers/usb/dwc2/core.h
@@ -1108,6 +1108,7 @@ struct dwc2_hsotg {
 
 	/* DWC OTG HW Release versions */
 #define DWC2_CORE_REV_4_30a	0x4f54430a
+#define DWC2_CORE_REV_2_70a	0x4f54270a
 #define DWC2_CORE_REV_2_71a	0x4f54271a
 #define DWC2_CORE_REV_2_72a     0x4f54272a
 #define DWC2_CORE_REV_2_80a	0x4f54280a
diff --git a/drivers/usb/dwc2/gadget.c b/drivers/usb/dwc2/gadget.c
index 102169b40419..9f02075ba15b 100644
--- a/drivers/usb/dwc2/gadget.c
+++ b/drivers/usb/dwc2/gadget.c
@@ -3449,6 +3449,19 @@ void dwc2_hsotg_core_init_disconnected(struct dwc2_hsotg *hsotg,
 	if (hsotg->params.ipg_isoc_en)
 		dcfg |= DCFG_IPG_ISOC_SUPPORDED;
 
+	/*
+	 * WA for Device Flushes Ongoing ISOC IN Packet at End-of-Periodic-Frame Boundary.
+	 * Once passed the end of periodic frame, and the controller is transmitting an
+	 * ISOC IN packet, the device fulshes the transmit FIFO. Tune periodic frame
+	 * interval to 95% instead of 80% to avoid it.
+	 */
+	if (using_desc_dma(hsotg) &&
+	    (hsotg->hw_params.snpsid >= DWC2_CORE_REV_2_70a &&
+	     hsotg->hw_params.snpsid <= DWC2_CORE_REV_4_00a)) {
+		dcfg &= ~DCFG_PERFRINT_MASK;
+		dcfg |= ((DCFG_PERFRINT_LIMIT << DCFG_PERFRINT_SHIFT) & DCFG_PERFRINT_MASK);
+	}
+
 	dwc2_writel(hsotg, dcfg,  DCFG);
 
 	/* Clear any pending OTG interrupts */

---
base-commit: 24a19b953e2a3d0ea5a8c4951a0ab8f32720c907
change-id: 20261014-dwc2-fix-wa-isoc-63a80e937000

Best regards,
--  
Fabrice Gasnier <fabrice.gasnier@foss.st.com>

Re: [PATCH] usb: dwc2: wa for isoc packet tx fifo flush at periodic frame boundary

[sashiko-bot]

> If an isochronous packet is still being transmitted, when the end of
> periodic frame interval elapses, using dma desc on dwc2 controller,
> the device wrongly flushes the pending packets from the tx fifo.
> This can lead to a huge packet is sent on the bus, leading to the host
> finally reset the bus, and re-enumerate it.
> 
> Workaround it by tuning the periodic frame interval limit from 80% to 95%,
> on the affected cores (2.70a to 4.00a). It makes the issue very unlikely
> to occur.
> 
> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261014-dwc2-fix-wa-isoc-v1-1-f261ce0852bd@foss.st.com?part=1