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

[Antony Pavlov]

On Mon, 24 Aug 2015 17:10:55 +0200
Lucas Stach <l.stach at pengutronix.de> wrote:

> Am Montag, den 24.08.2015, 17:35 +0300 schrieb Antony Pavlov:
> > On Mon, 24 Aug 2015 10:49:10 +0200
> > Sascha Hauer <s.hauer at pengutronix.de> wrote:
> > 
> > > On Thu, Aug 20, 2015 at 06:22:18PM +0300, Peter Mamonov wrote:
> > > > 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 at 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));
> > > 
> > > This doesn't look very nice since we modify a ch9 defined struct just for
> > > the sake of using it in an array somewhere else. We can fix it like
> > > this, but please add a comment why we need this.
> > 
> > We need some fix here to make EHCI works on MIPS architecture.
> > On the other hand the ch9 header file is used in linux kernel and in U-boot.
> > I don't know, does U-boot EHCI driver works on mips (though AFAIR there was a USB MIPS-related
> > patch several days ago), but linux kernel work with this ch9 header succesfully on MIPS.
> > So another way to fix the problem is to port some code from modern U-boot or linux.
> > 
> The question here is: why isn't the compiler emitting the correct
> instruction?
> 
> Apparently MIPS has a "ulh" instruction to load (possibly) unaligned
> halfwords. The placement of the wMaxPacketSize member is static and the
> compiler should be able to figure out that it may be placed at an
> unaligned position, as requested per the packed attribute attached to
> struct usb_endpoint_descriptor.
> 
> This isn't a problem we should fix in the barebox code unless we know
> exactly why the compiler is doing the wrong thing.

wMaxPacketSize unaligned access is the most simple EHCI problem on MIPS :)
I have my private AR9331 big-endian EHCI branch.
I'll try to check it in several days and submit the patches.

-- 
Best regards,
  Antony Pavlov