USB: xhci: Remove packed attribute from structures.

The packed attribute allows gcc to muck with the alignment of data
structures, which may lead to byte-wise writes that break atomicity of
writes.  Packed should only be used when the compile may add undesired
padding to the structure.  Each element of the structure will be aligned
by C based on its size and the size of the elements around it.  E.g. a u64
would be aligned on an 8 byte boundary, the next u32 would be aligned on a
four byte boundary, etc.

Since most of the xHCI structures contain only u32 bit values, removing
the packed attribute for them should be harmless.  (A future patch will
change some of the twin 32-bit address fields to one 64-bit field, but all
those places have an even number of 32-bit fields before them, so the
alignment should be correct.)  Add BUILD_BUG_ON statements to check that
the compiler doesn't add padding to the data structures that have a
hardware-defined layout.

While we're modifying the registers, change the name of intr_reg to
xhci_intr_reg to avoid global conflicts.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 19 insertions, 0 deletions

diff --git a/drivers/usb/host/xhci-hcd.c b/drivers/usb/host/xhci-hcd.c
index c6b921994b28..59ee61d2a198 100644
--- a/drivers/usb/host/xhci-hcd.c
+++ b/drivers/usb/host/xhci-hcd.c
@@ -1243,6 +1243,25 @@ static int __init xhci_hcd_init(void)
 		return retval;
 	}
 #endif
+	/*
+	 * Check the compiler generated sizes of structures that must be laid
+	 * out in specific ways for hardware access.
+	 */
+	BUILD_BUG_ON(sizeof(struct xhci_doorbell_array) != 256*32/8);
+	BUILD_BUG_ON(sizeof(struct xhci_slot_ctx) != 8*32/8);
+	BUILD_BUG_ON(sizeof(struct xhci_ep_ctx) != 8*32/8);
+	/* xhci_device_control has eight fields, and also
+	 * embeds one xhci_slot_ctx and 31 xhci_ep_ctx
+	 */
+	BUILD_BUG_ON(sizeof(struct xhci_device_control) != (8+8+8*31)*32/8);
+	BUILD_BUG_ON(sizeof(struct xhci_stream_ctx) != 4*32/8);
+	BUILD_BUG_ON(sizeof(union xhci_trb) != 4*32/8);
+	BUILD_BUG_ON(sizeof(struct xhci_erst_entry) != 4*32/8);
+	BUILD_BUG_ON(sizeof(struct xhci_cap_regs) != 7*32/8);
+	BUILD_BUG_ON(sizeof(struct xhci_intr_reg) != 8*32/8);
+	/* xhci_run_regs has eight fields and embeds 128 xhci_intr_regs */
+	BUILD_BUG_ON(sizeof(struct xhci_run_regs) != (8+8*128)*32/8);
+	BUILD_BUG_ON(sizeof(struct xhci_doorbell_array) != 256*32/8);
 	return 0;
 }
 module_init(xhci_hcd_init);