Re: r8712u driver - on ARM

[Larry Finger <Larry.Finger@lwfinger.net>]

On 10/01/2011 11:22 AM, Christian Lamparter wrote:
> On Saturday 01 October 2011 18:01:08 Larry Finger wrote:
>> Ian,
>>
>> Most of the skb assignments in r8712u are aligned OK and most aligned on
>> 512-byte boundaries, but there was one that had the minimal offset of 14 bytes.
>> The attached patch should fix it. Does it help?
> Interesting, this "patch" goes in a completely different direction.
> Can you tell me where the driver aligns the frames which will be
> xmitted by the device [i.e.: which is passed to the usb subsystem
> by usb_submit_urb]? Because that's what actually matters.

In this driver, all references are to _usb_submit_urb(), which is defined to be 
usb_submit_urb() in one of the header files. That made it easy to insert a test 
for misalignment of the DMA buffer as follows:

Index: wireless-testing-new/drivers/staging/rtl8712/osdep_service.h
===================================================================
--- wireless-testing-new.orig/drivers/staging/rtl8712/osdep_service.h
+++ wireless-testing-new/drivers/staging/rtl8712/osdep_service.h
@@ -34,7 +34,7 @@
  #include <linux/if_arp.h>
  #include <linux/firmware.h>
  #define   _usb_alloc_urb(x, y)       usb_alloc_urb(x, y)
-#define   _usb_submit_urb(x, y)     usb_submit_urb(x, y)
+//#define   _usb_submit_urb(x, y)     usb_submit_urb(x, y)

  struct __queue {
         struct  list_head       queue;
@@ -232,5 +232,13 @@ static inline u32 _RND512(u32 sz)
         return ((sz >> 9) + ((sz & 511) ? 1 : 0)) << 9;
  }

+static inline int _usb_submit_urb(struct urb *urb, gfp_t mem_flags)
+{
+       if (urb->transfer_dma & 3) {
+               pr_info("Transfer_dma 0x%x not on 4-byte boundary\n", 
(uint)urb->transfer_dma);
+               dump_stack();
+       }
+       return usb_submit_urb(urb, mem_flags);
+}
  #endif

I never hit the pr_info() and the associated dump_stack(). If that test is 
sufficient, then buffer misalignment is not the source of the problem.

Larry