Hi,
On 16.02.2017 17:37, David Laight wrote:
> From: Lino Sanfilippo
>> Sent: 16 February 2017 16:02
> ...
>> I was referring to the copy of tx descriptors, not the frames/fragments
>> itself.
>> I wrote "tx buffers" because in this driver a descriptor is represented as
>> a struct "aq_ring_buff_s". I cannot see a reason why this descriptor copy
>> should be necessary.
>
> Not unless the descriptor memory is on the card.
>
> Actually it might be worse than that.
> The transmit descriptor probably has an 'owner' bit.
> The write of the word containing that bit must be last and
> preceded by the appropriate barrier (probably dma_wmb()).
> Another barrier is needed before the 'doorbell' io write that kicks
> the hardware.
>
After taking a look at the concerning code parts, I can say that there is
at least no barrier to ensure dma flush before the doorbell.
What about the patch below to fix this?
Regards,
Lino
Subject: [PATCH] net: aquantia: add memory barrier before tx descriptors are
passed to the hardware
Add a memory barrier to ensure that tx descriptors are written completely
before the descriptors are passed to the hardware.
Signed-off-by: Lino Sanfilippo <linosanfili...@gmx.de>
Suggested-by: David Laight <david.lai...@aculab.com>
---
drivers/net/ethernet/aquantia/atlantic/hw_atl/hw_atl_llh.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/net/ethernet/aquantia/atlantic/hw_atl/hw_atl_llh.c
b/drivers/net/ethernet/aquantia/atlantic/hw_atl/hw_atl_llh.c
index 3de651a..c3d73e7 100644
--- a/drivers/net/ethernet/aquantia/atlantic/hw_atl/hw_atl_llh.c
+++ b/drivers/net/ethernet/aquantia/atlantic/hw_atl/hw_atl_llh.c
@@ -526,6 +526,8 @@ void reg_tx_dma_desc_base_addressmswset(struct aq_hw_s
*aq_hw,
void reg_tx_dma_desc_tail_ptr_set(struct aq_hw_s *aq_hw,
u32 tx_dma_desc_tail_ptr, u32 descriptor)
{
+ /* make sure writes to dma descriptors are completed */
+ wmb();
aq_hw_write_reg(aq_hw, tx_dma_desc_tail_ptr_adr(descriptor),
tx_dma_desc_tail_ptr);
}
--
2.7.4
