[PATCH 2/2] USB: EHCI: Add alias for Broadcom INSNREG

[Kees Cook]

Refactor struct ehci_regs to avoid accessing beyond the end of
port_status. This change results in no difference in the resulting
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 is
confusing. If "USB_EHCI_INSNREG00" is at port_status[0x0f], its offset
would be 0x80 (not 0x90). The code uses port_status[0x10], so is that
not using "USB_EHCI_INSNREG00"?

Perhaps port_status[0x10] is USB_EHCI_INSNREG01 and port_status[0x12]
is USB_EHCI_INSNREG03? If so, the union could be adjusted to better
represent the layout.

Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Al Cooper <alcooperx@xxxxxxxxx>
Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Cc: linux-usb@xxxxxxxxxxxxxxx
Cc: bcm-kernel-feedback-list@xxxxxxxxxxxx
Suggested-by: Arnd Bergmann <arnd@xxxxxxxx>
Fixes: 9df231511bd6 ("usb: ehci: Add new EHCI driver for Broadcom STB SoC's")
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 drivers/usb/host/ehci-brcm.c | 11 +++++------
 include/linux/usb/ehci_def.h | 16 ++++++++++++++--
 2 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/drivers/usb/host/ehci-brcm.c b/drivers/usb/host/ehci-brcm.c
index 3e0ebe8cc649..5d232d3701f9 100644
--- a/drivers/usb/host/ehci-brcm.c
+++ b/drivers/usb/host/ehci-brcm.c
@@ -110,8 +110,8 @@ static int ehci_brcm_reset(struct usb_hcd *hcd)
 	 *   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[0]);
+	ehci_writel(ehci, 0x00000001, &ehci->regs->brcm_insnreg[2]);
 
 	return ehci_setup(hcd);
 }
@@ -223,11 +223,10 @@ 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
+	 * 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[0]);
+	ehci_writel(ehci, 0x00000001, &ehci->regs->brcm_insnreg[2]);
 
 	ehci_resume(hcd, false);
 
diff --git a/include/linux/usb/ehci_def.h b/include/linux/usb/ehci_def.h
index 5398f571113b..86f0909cab99 100644
--- a/include/linux/usb/ehci_def.h
+++ b/include/linux/usb/ehci_def.h
@@ -182,11 +182,23 @@ struct ehci_regs {
  * its EHCI controller has both TT and LPM support. HOSTPCx are extensions to
  * PORTSCx
  */
-	/* HOSTPC: offset 0x84 */
-	u32		hostpc[HCS_N_PORTS_MAX];
+	union {
+		/* 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 */
 
+		/*
+		 * This was originally documented as:
+		 * "port_status[0x0f] = Broadcom-proprietary USB_EHCI_INSNREG00 @ 0x90"
+		 * but this doesn't make sense: the code was using
+		 * port_status[0x10]. port_status[0x0f] would be reserved4.
+		 * Also, none of these are near 0x90. port_status[0x10] is
+		 * offset 0x84, and port_status[0x0f] would be 0x80.
+		 */
+		u32	brcm_insnreg[3];
+	};
+
 	u32		reserved5[2];
 
 	/* USBMODE_EX: offset 0xc8 */
-- 
2.30.2