[PATCH] RFC: include/usb/ch9.h: pad usb_endpoint_descriptor with 1 byte

[Peter Mamonov <pmamonov@gmail.com>]

This patch fixes "Ooops, address error on load or ifetch!",
caused by "usb" command on MIPS architecture.

To reproduce the problem follow the following steps:

1. Build barebox for MIPS target with -O0 optimization flag:

diff --git a/Makefile b/Makefile
index 5a7fd5f..da9a8be 100644
--- a/Makefile
+++ b/Makefile
@@ -301,7 +301,7 @@ CPPFLAGS        := -D__KERNEL__ -D__BAREBOX__ $(LINUXINCLUDE) -fno-builtin -ffre

 CFLAGS          := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
                    -Werror-implicit-function-declaration \
-                   -fno-strict-aliasing -fno-common -Os -pipe
+                   -fno-strict-aliasing -fno-common -O0 -pipe
 AFLAGS          := -D__ASSEMBLY__

 LDFLAGS_barebox        := -Map barebox.map

2. Plug in a usb flash drive.

3. Run the "usb" command:

	barebox@QEMU DUNA:/ usb -s
	USB: scanning bus for devices...
	&(dev->config.interface[0].ep_desc[0].wMaxPacketSize) = a042732a
	Bus 001 Device 001: ID 0000:0000 EHCI Host Controller
	&(dev->config.interface[0].ep_desc[0].wMaxPacketSize) = a0429f02
	&(dev->config.interface[0].ep_desc[1].wMaxPacketSize) = a0429f0b

	Ooops, address error on load or ifetch!

	$ 0   : 00000000 00000000 a0429f0b a0429de4
	$ 4   : 00000000 0000000a 00000000 000687e0
	$ 8   : 00000000 00000000 00000000 fa000000
	$12   : 00000001 00000004 00000000 00000000
	$16   : 00000000 00000000 00000000 00000000
	$20   : 00000000 00000000 00000000 00000000
	$24   : 00000000 00000000
	$28   : 00000000 a03ffb40 a03ffb40 a082e9f4
	Hi    : 00000000
	Lo    : 00000000
	epc   : a082ea38
	ra    : a082e9f4
	Status: b4000002
	Cause : 00008010
	Config: 88d0c083

	### ERROR ### Please RESET the board ###

The source of the error is the following line of code from the usb_parse_config() function:

			le16_to_cpus(&(dev->config.interface[ifno].ep_desc[epno].\
							       wMaxPacketSize));

Which tries to load half-word from an un-aligned address 0xa0429f0b stored in v0:

a082ea38:       94420000        lhu     v0,0(v0)

0xa0429f0b is an address of wMaxPacketSize member of a struct usb_endpoint_descriptor at offset 4:

struct usb_endpoint_descriptor {
	__u8  bLength;
	__u8  bDescriptorType;
	__u8  bEndpointAddress;
	__u8  bmAttributes;
	__le16 wMaxPacketSize;
	__u8  bInterval;
	__u8  bRefresh;
	__u8  bSynchAddress;
} __attribute__ ((packed));

The instances of the usb_endpoint_descriptor are stored in a "ep_desc" array:

struct usb_interface {
	...
	struct usb_endpoint_descriptor ep_desc[USB_MAXENDPOINTS];
};

Since the size of the usb_endpoint_descriptor is odd (9 bytes),
the second element of the ep_desc array is un-aligned,
as well as it's member wMaxPacketSize:

Bus 001 Device 001: ID 0000:0000 EHCI Host Controller
&(dev->config.interface[0].ep_desc[0].wMaxPacketSize) = a0429f02
&(dev->config.interface[0].ep_desc[1].wMaxPacketSize) = a0429f0b

A possible fix to this problem is to make the size of the usb_endpoint_descriptor even.
---
 include/usb/ch9.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/usb/ch9.h b/include/usb/ch9.h
index ab5d531..5b261e6 100644
--- a/include/usb/ch9.h
+++ b/include/usb/ch9.h
@@ -379,6 +379,7 @@ struct usb_endpoint_descriptor {
 	/* use USB_DT_ENDPOINT*_SIZE in bLength, not sizeof. */
 	__u8  bRefresh;
 	__u8  bSynchAddress;
+	__u8  fill;
 } __attribute__ ((packed));
 
 #define USB_DT_ENDPOINT_SIZE		7
-- 
2.1.4


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