sfc: Use 64-bit writes for TX push where possible

This was originally done as part of commit
65f0b417 ("sfc: Use write-combining to
reduce TX latency"), but that had to be reverted.
Signed-off-by: NBen Hutchings <bhutchings@solarflare.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/sfc/io.h

@@ -48,9 +48,9 @@
  *   replacing the low 96 bits with zero does not affect functionality.
  * - If the host writes to the last dword address of such a register
  *   (i.e. the high 32 bits) the underlying register will always be
- *   written.  If the collector does not hold values for the low 96
- *   bits of the register, they will be written as zero.  Writing to
- *   the last qword does not have this effect and must not be done.
+ *   written.  If the collector and the current write together do not
+ *   provide values for all 128 bits of the register, the low 96 bits
+ *   will be written as zero.
  * - If the host writes to the address of any other part of such a
  *   register while the collector already holds values for some other
  *   register, the write is discarded and the collector maintains its
@@ -237,12 +237,13 @@ static inline void _efx_writeo_page(struct efx_nic *efx, efx_oword_t *value,
 
 #ifdef EFX_USE_QWORD_IO
 	_efx_writeq(efx, value->u64[0], reg + 0);
+	_efx_writeq(efx, value->u64[1], reg + 8);
 #else
 	_efx_writed(efx, value->u32[0], reg + 0);
 	_efx_writed(efx, value->u32[1], reg + 4);
-#endif
 	_efx_writed(efx, value->u32[2], reg + 8);
 	_efx_writed(efx, value->u32[3], reg + 12);
+#endif
 }
 #define efx_writeo_page(efx, value, reg, page)				\
 	_efx_writeo_page(efx, value,					\