[U-Boot] [RFC PATCH] usb: ehci: do not invalidate a NULL buffer

[Dirk Behme]

Its a valid use case to call ehci_submit_async() with a NULL buffer
with length 0. E.g. from usb_set_configuration().

As invalidate_dcache_range() isn't able to judge if the address
NULL is valid or not (depending on the SoC hardware configuration it
might be valid) do the check in ehci_submit_async() as here we know
that we don't have to invalidate such a buffer.

Signed-off-by: Dirk Behme <dirk.behme at de.bosch.com>

---
Notes:

This was found on an older vendor specific U-Boot on an ARMv8 SoC
with a MMU configuration where address 0x00000000 is invalid.

The callstack I've seen is

usb_set_configuration(), calls
 -> usb_control_msg() with *data == NULL and size == 0
  -> submit_control_msg()
   -> _ehci_submit_control_msg()
    -> ehci_submit_async()

ehci_submit_async() called  __asm_invalidate_dcache_range() from
arch/arm/cpu/armv8/cache.S, then. Resulting in an exception trying
to use address 0 in x0 (dc ivac, x0).

I'm slightly unsure why this hasn't been catched or complained about
previously, already. Maybe I missed anything while working with an older
vendor U-Boot? Sorry in this case.

Best regards

Dirk
---
 drivers/usb/host/ehci-hcd.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
index be3e842dcc..32c661b37e 100644
--- a/drivers/usb/host/ehci-hcd.c
+++ b/drivers/usb/host/ehci-hcd.c
@@ -595,8 +595,9 @@ ehci_submit_async(struct usb_device *dev, unsigned long pipe, void *buffer,
 	 * dangerous operation, it's responsibility of the calling
 	 * code to make sure enough space is reserved.
 	 */
-	invalidate_dcache_range((unsigned long)buffer,
-		ALIGN((unsigned long)buffer + length, ARCH_DMA_MINALIGN));
+	if (buffer != NULL && length > 0)
+		invalidate_dcache_range((unsigned long)buffer,
+			ALIGN((unsigned long)buffer + length, ARCH_DMA_MINALIGN));
 
 	/* Check that the TD processing happened */
 	if (QT_TOKEN_GET_STATUS(token) & QT_TOKEN_STATUS_ACTIVE)
-- 
2.14.1