USB: EHCI: Add alias for Broadcom INSNREG

Refactor struct ehci_regs to avoid accessing beyond the end of
port_status. This change results in no difference in the final
object code.

Avoids several warnings when building with -Warray-bounds:

drivers/usb/host/ehci-brcm.c: In function 'ehci_brcm_reset':
drivers/usb/host/ehci-brcm.c:113:32: warning: array subscript 16 is above array bounds of 'u32[15]' {aka 'unsigned int[15]'} [-Warray-bounds]
  113 |  ehci_writel(ehci, 0x00800040, &ehci->regs->port_status[0x10]);
      |                                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from drivers/usb/host/ehci.h:274,
                 from drivers/usb/host/ehci-brcm.c:15:
./include/linux/usb/ehci_def.h:132:7: note: while referencing 'port_status'
  132 |   u32 port_status[HCS_N_PORTS_MAX];
      |       ^~~~~~~~~~~

Note that the documentation around this proprietary register was
confusing. If "USB_EHCI_INSNREG00" is at port_status[0x0f], its offset
would be 0x80 (not 0x90). The comments have been adjusted to fix this
apparent typo.

Fixes: 9df23151 ("usb: ehci: Add new EHCI driver for Broadcom STB SoC's")
Cc: Al Cooper <alcooperx@gmail.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-usb@vger.kernel.org
Cc: bcm-kernel-feedback-list@broadcom.com
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210818173018.2259231-3-keescook@chromium.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/ehci-brcm.c

@@ -108,10 +108,9 @@ static int ehci_brcm_reset(struct usb_hcd *hcd)
 	/*
 	 * SWLINUX-1705: Avoid OUT packet underflows during high memory
 	 *   bus usage
-	 * port_status[0x0f] = Broadcom-proprietary USB_EHCI_INSNREG00 @ 0x90
 	 */
-	ehci_writel(ehci, 0x00800040, &ehci->regs->port_status[0x10]);
-	ehci_writel(ehci, 0x00000001, &ehci->regs->port_status[0x12]);
+	ehci_writel(ehci, 0x00800040, &ehci->regs->brcm_insnreg[1]);
+	ehci_writel(ehci, 0x00000001, &ehci->regs->brcm_insnreg[3]);
 
 	return ehci_setup(hcd);
 }
@@ -223,11 +222,9 @@ static int __maybe_unused ehci_brcm_resume(struct device *dev)
 	/*
 	 * SWLINUX-1705: Avoid OUT packet underflows during high memory
 	 *   bus usage
-	 * port_status[0x0f] = Broadcom-proprietary USB_EHCI_INSNREG00
-	 * @ 0x90
 	 */
-	ehci_writel(ehci, 0x00800040, &ehci->regs->port_status[0x10]);
-	ehci_writel(ehci, 0x00000001, &ehci->regs->port_status[0x12]);
+	ehci_writel(ehci, 0x00800040, &ehci->regs->brcm_insnreg[1]);
+	ehci_writel(ehci, 0x00000001, &ehci->regs->brcm_insnreg[3]);
 
 	ehci_resume(hcd, false);
 

include/linux/usb/ehci_def.h

@@ -176,16 +176,23 @@ struct ehci_regs {
 #define USBMODE_CM_HC	(3<<0)		/* host controller mode */
 #define USBMODE_CM_IDLE	(0<<0)		/* idle state */
 	};
-	u32		reserved4;
 
 /* Moorestown has some non-standard registers, partially due to the fact that
  * its EHCI controller has both TT and LPM support. HOSTPCx are extensions to
  * PORTSCx
  */
-	/* HOSTPC: offset 0x84 */
-	u32		hostpc[HCS_N_PORTS_MAX];
+	union {
+		struct {
+			u32	reserved4;
+			/* HOSTPC: offset 0x84 */
+			u32	hostpc[HCS_N_PORTS_MAX];
 #define HOSTPC_PHCD	(1<<22)		/* Phy clock disable */
 #define HOSTPC_PSPD	(3<<25)		/* Port speed detection */
+		};
+
+		/* Broadcom-proprietary USB_EHCI_INSNREG00 @ 0x80 */
+		u32	brcm_insnreg[4];
+	};
 
 	u32		reserved5[2];