[PATCH v3] usb: dwc3: core: Prevent USB core invalid event buffer address access

[Selvarasu Ganesan <selvarasu.g@samsung.com>]

This commit addresses an issue where the USB core could access an
invalid event buffer address during runtime suspend, potentially causing
SMMU faults and other memory issues in Exynos platforms. The problem
arises from the following sequence.
        1. In dwc3_gadget_suspend, there is a chance of a timeout when
        moving the USB core to the halt state after clearing the
        run/stop bit by software.
        2. In dwc3_core_exit, the event buffer is cleared regardless of
        the USB core's status, which may lead to an SMMU faults and
        other memory issues. if the USB core tries to access the event
        buffer address.

To prevent this hardware quirk on Exynos platforms, this commit ensures
that the event buffer address is not cleared by software  when the USB
core is active during runtime suspend by checking its status before
clearing the buffer address.

Cc: stable@vger.kernel.org # v6.1+
Signed-off-by: Selvarasu Ganesan <selvarasu.g@samsung.com>
---

Changes in v3:
- Added comment on why we need this fix.
- Included platform name in commit message.
- Removed Fixes tag as no issue on the previous commits, and updated Cc tag.
- Link to v2: https://lore.kernel.org/lkml/20240808120507.1464-1-selvarasu.g@samsung.com/

Changes in v2:
- Added separate check for USB controller status before cleaning the
  event buffer.
- Link to v1: https://lore.kernel.org/lkml/20240722145617.537-1-selvarasu.g@samsung.com/
---
 drivers/usb/dwc3/core.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index 734de2a8bd21..ccc3895dbd7f 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -564,9 +564,17 @@ int dwc3_event_buffers_setup(struct dwc3 *dwc)
 void dwc3_event_buffers_cleanup(struct dwc3 *dwc)
 {
 	struct dwc3_event_buffer	*evt;
+	u32				reg;
 
 	if (!dwc->ev_buf)
 		return;
+	/*
+	 * Exynos platforms may not be able to access event buffer if the
+	 * controller failed to halt on dwc3_core_exit().
+	 */
+	reg = dwc3_readl(dwc->regs, DWC3_DSTS);
+	if (!(reg & DWC3_DSTS_DEVCTRLHLT))
+		return;
 
 	evt = dwc->ev_buf;
 
-- 
2.17.1