On 21.8.2019 6.18, Peter Chen wrote:
According to xHCI 1.1 CH4.19.4 Port Power:
While Chip Hardware Reset or HCRST is asserted,
the value of PP is undefined. If the xHC supports
power switches (PPC = ‘1’) then VBus may be deasserted
during this time. PP (and VBus) shall be enabled immediately
upon exiting the reset condition.
The VBus glitch may cause some USB devices work abnormal, we observe
it at NXP LS1012AFWRY/LS1043ARDB/LX2160AQDS/LS1088ARDB platforms. To
avoid this Vbus glitch, we could set PP as 0 before HCRST, and the PP
will back to 1 after HCRST according to spec.
Is this glitch causing issues already at the first xHC reset when we are
loading the xhci driver, or only later resets, like xHC reset at resume?
Reported-by: Ran Wang <ran.wang_1@xxxxxxx>
Signed-off-by: Peter Chen <peter.chen@xxxxxxx>
---
drivers/usb/host/xhci.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)
diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 6b34a573c3d9..f5a7b5d63031 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -167,7 +167,8 @@ int xhci_reset(struct xhci_hcd *xhci)
{
u32 command;
u32 state;
- int ret;
+ int ret, i;
+ u32 portsc;
state = readl(&xhci->op_regs->status);
@@ -181,6 +182,18 @@ int xhci_reset(struct xhci_hcd *xhci)
return 0;
}
+ /*
+ * Keep PORTSC.PP as 0 before HCRST to eliminate
+ * Vbus glitch, see CH 4.19.4.
+ */
+ for (i = 0; i < HCS_MAX_PORTS(xhci->hcs_params1); i++) {
+ __le32 __iomem *port_addr = &xhci->op_regs->port_status_base +
+ NUM_PORT_REGS * i;
+ portsc = readl(port_addr);
+ portsc &= ~PORT_POWER;
+ writel(portsc, port_addr);
Not all bits read from PORTSC should be written back, you might need
portsc = xhci_port_state_to_neutral(portsc) here.
Normally I'd recommend using the xhci_set_port_power() helper instead, but
if this is is needed at driver load time then port arrays may not be set up yet.
xhci_set_port_power() would take care of possible ACPI method calls, and add some debugging.
Not sure if this will impact some other platforms, maybe it would be better to move this to
a separate function, and call it before xhci_reset() if a quirk is set.
-Mathias
