port_enable and port_reset must change atomically.

I have observed two separate EHCI host bridges that do not tolerate
using C bit-fields to directly manipulate the portsc_t register.  The
reason for this is that the EHCI spec says that port_enable must go
to 0 at the time that port_reset goes to 1.  Naturally this cannot be
done using direct bit-field manipulation.  Instead, we use a temporary
variable, change the bit-fields there, then atomically write the new
value back to the hardware.

Signed-off-by: Steven A. Falco <sfalco@coincident.com>
Change-Id: If138faee43e0293efa203b86f7893fdf1e811269
Reviewed-on: http://review.coreboot.org/101
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>

diff --git a/payloads/libpayload/drivers/usb/ehci_rh.c b/payloads/libpayload/drivers/usb/ehci_rh.c
index 5eaeeb690eeb5104601c6bb735ccb4bbd695c51a..5f0db94b8d2b9792468b541cba06658ca4e6729e 100644 (file)
--- a/payloads/libpayload/drivers/usb/ehci_rh.c
+++ b/payloads/libpayload/drivers/usb/ehci_rh.c
@@ -54,14 +54,19 @@ static void
 ehci_rh_hand_over_port (usbdev_t *dev, int port)
 {
        volatile portsc_t *p = &(RH_INST(dev)->ports[port]);
+       volatile portsc_t tmp;
 
        printf("giving up port %x, it's USB1\n", port+1);
 
        /* Lowspeed device. Hand over to companion */
-       p->port_owner = 1;
+       tmp = *p;
+       tmp.port_owner = 1;
+       *p = tmp;
        do {} while (!p->conn_status_change);
        /* RW/C register, so clear it by writing 1 */
-       p->conn_status_change = 1;
+       tmp = *p;
+       tmp.conn_status_change = 1;
+       *p = tmp;
        return;
 }
 
@@ -69,6 +74,7 @@ static void
 ehci_rh_scanport (usbdev_t *dev, int port)
 {
        volatile portsc_t *p = &(RH_INST(dev)->ports[port]);
+       volatile portsc_t tmp;
        if (RH_INST(dev)->devices[port]!=-1) {
                printf("Unregister device at port %x\n", port+1);
                usb_detach_device(dev->controller, RH_INST(dev)->devices[port]);
@@ -81,10 +87,22 @@ ehci_rh_scanport (usbdev_t *dev, int port)
                        ehci_rh_hand_over_port(dev, port);
                        return;
                }
-               p->port_enable = 0;
-               p->port_reset = 1;
+
+               /* Deassert enable, assert reset.  These must change
+                * atomically.
+                */
+               tmp = *p;
+               tmp.port_enable = 0;
+               tmp.port_reset = 1;
+               *p = tmp;
+
+               /* Wait a bit while reset is active. */
                mdelay(50);
-               p->port_reset = 0;
+
+               /* Deassert reset. */
+               tmp.port_reset = 0;
+               *p = tmp;
+
                /* Wait for flag change to finish. The controller might take a while */
                while (p->port_reset) ;
                if (!p->port_enable) {
@@ -95,7 +113,9 @@ ehci_rh_scanport (usbdev_t *dev, int port)
                RH_INST(dev)->devices[port] = usb_attach_device(dev->controller, dev->address, port, 2);
        }
        /* RW/C register, so clear it by writing 1 */
-       p->conn_status_change = 1;
+       tmp = *p;
+       tmp.conn_status_change = 1;
+       *p = tmp;
 }
 
 static int
@@ -122,6 +142,8 @@ void
 ehci_rh_init (usbdev_t *dev)
 {
        int i;
+       volatile portsc_t *p;
+       volatile portsc_t tmp;
 
        dev->destroy = ehci_rh_destroy;
        dev->poll = ehci_rh_poll;
@@ -135,8 +157,11 @@ ehci_rh_init (usbdev_t *dev)
 
        RH_INST(dev)->devices = malloc(RH_INST(dev)->n_ports * sizeof(int));
        for (i=0; i < RH_INST(dev)->n_ports; i++) {
+               p = &(RH_INST(dev)->ports[i]);
                RH_INST(dev)->devices[i] = -1;
-               RH_INST(dev)->ports[i].pp = 1;
+               tmp = *p;
+               tmp.pp = 1;
+               *p = tmp;
        }
 
        dev->address = 0;