[PATCH] bcmgenet: fix DMA buffer management

[Jason Wessel]

On 7/16/20 7:02 AM, Jason Wessel wrote:
> On 7/9/20 3:11 AM, etienne.duble at gmail.com wrote:
>> From: Etienne Dublé <etienne.duble at imag.fr>
>>
>> This commit fixes a serious issue occuring when several network
>> commands are run on a raspberry pi 4 board: for instance a "dhcp"
>> command and then one or several "tftp" commands. In this case,
>> packet recv callbacks were called several times on the same packets,
>> and send function was failing most of the time.
>>
>> note: if the boot procedure is made of a single network
>> command, the issue is not visible.
>>
>> The issue is related to management of the packet ring buffers
>> (producer / consumer) and DMA.
>> Each time a packet is received, the ethernet device stores it
>> in the buffer and increments an index called RDMA_PROD_INDEX.
>> Each time the driver outputs a received packet, it increments
>> another index called RDMA_CONS_INDEX.
>>
>> Between each pair of network commands, as part of the driver
>> 'start' function, previous code tried to reset both RDMA_CONS_INDEX
>> and RDMA_PROD_INDEX to 0. But RDMA_PROD_INDEX cannot be written from
>> driver side, thus its value was actually not updated, and only
>> RDMA_CONS_INDEX was reset to 0. This was resulting in a major
>> synchronization issue between the driver and the device. Most
>> visible bahavior was that the driver seemed to receive again the
>> packets from the previous commands (e.g. DHCP response packets
>> "received" again when performing the first TFTP command).
>>
>> This fix consists in setting RDMA_CONS_INDEX to the same
>> value as RDMA_PROD_INDEX, when resetting the driver.
>>
>> The same kind of fix was needed on the TX side, and a few variables
>> had to be reset accordingly (c_index, tx_index, rx_index).
> 
> 
> While there is some kind of problem with the driver, because I too
> have observed a problem with multiple requests timing out or failing,
> this patch makes the problem much worse.  I was only able to complete
> a single tftp request. 
> 
> In my case I am using a static IP address and serverip. 
> 
> Also your patch was missing the sign-off line.  Please consider
> running your patches through scripts/checkpatch.pl.
> 
> Cheers,
> Jason.
> 
>> ---
>>  drivers/net/bcmgenet.c | 15 +++++++--------
>>  1 file changed, 7 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/net/bcmgenet.c b/drivers/net/bcmgenet.c
>> index 11b6148ab6..a4facfd63f 100644
>> --- a/drivers/net/bcmgenet.c
>> +++ b/drivers/net/bcmgenet.c
>> @@ -378,8 +378,6 @@ static void rx_descs_init(struct bcmgenet_eth_priv *priv)
>>  	u32 len_stat, i;
>>  	void *desc_base = priv->rx_desc_base;
>>  
>> -	priv->c_index = 0;
>> -
>>  	len_stat = (RX_BUF_LENGTH << DMA_BUFLENGTH_SHIFT) | DMA_OWN;
>>  
>>  	for (i = 0; i < RX_DESCS; i++) {
>> @@ -403,8 +401,10 @@ static void rx_ring_init(struct bcmgenet_eth_priv *priv)
>>  	writel(RX_DESCS * DMA_DESC_SIZE / 4 - 1,
>>  	       priv->mac_reg + RDMA_RING_REG_BASE + DMA_END_ADDR);
>>  
>> -	writel(0x0, priv->mac_reg + RDMA_PROD_INDEX);
>> -	writel(0x0, priv->mac_reg + RDMA_CONS_INDEX);
>> +	/* cannot init RDMA_PROD_INDEX to 0, so align RDMA_CONS_INDEX on it instead */
>> +	priv->c_index = readl(priv->mac_reg + RDMA_PROD_INDEX);
>> +	writel(priv->c_index, priv->mac_reg + RDMA_CONS_INDEX);
>> +	priv->rx_index = priv->c_index;


	printf("before RX_IDX: 0x%x\n", priv->rx_index);

I added a printf() like above for the RX and TX to see what is going on when 
I try and transfer a kernel Image file the second time.


U-Boot> tftp ${loadaddr} bootfs/Image
before RX_IDX: 0x0
before TX_IDX: 0x0
Using ethernet at 7d580000 device
Filename 'bootfs/Image'.
Load address: 0x80000
Loading: ## Warning: gatewayip needed but not set
##################################################  16.8 MiB
         6.1 MiB/s
done
Bytes transferred = 17615360 (10cca00 hex)
U-Boot> tftp ${loadaddr} bootfs/Image
before RX_IDX: 0xe4
before TX_IDX: 0x2ee3
Using ethernet at 7d580000 device
Filename 'bootfs/Image'.
Load address: 0x80000
Loading: ## Warning: gatewayip needed but not set



The TX_IDX is now 0x2ee3 which is definitely not going to work.

According to the driver file there are only 256 (0xFF) slots,
which is why it hangs, with your change. 

Jason.

>>  	writel((RX_DESCS << DMA_RING_SIZE_SHIFT) | RX_BUF_LENGTH,
>>  	       priv->mac_reg + RDMA_RING_REG_BASE + DMA_RING_BUF_SIZE);
>>  	writel(DMA_FC_THRESH_VALUE, priv->mac_reg + RDMA_XON_XOFF_THRESH);
>> @@ -421,8 +421,9 @@ static void tx_ring_init(struct bcmgenet_eth_priv *priv)
>>  	writel(0x0, priv->mac_reg + TDMA_WRITE_PTR);
>>  	writel(TX_DESCS * DMA_DESC_SIZE / 4 - 1,
>>  	       priv->mac_reg + TDMA_RING_REG_BASE + DMA_END_ADDR);
>> -	writel(0x0, priv->mac_reg + TDMA_PROD_INDEX);
>> -	writel(0x0, priv->mac_reg + TDMA_CONS_INDEX);
>> +	/* cannot init TDMA_CONS_INDEX to 0, so align TDMA_PROD_INDEX on it instead */
>> +	priv->tx_index = readl(priv->mac_reg + TDMA_CONS_INDEX);
>> +	writel(priv->tx_index, priv->mac_reg + TDMA_PROD_INDEX);
>>  	writel(0x1, priv->mac_reg + TDMA_RING_REG_BASE + DMA_MBUF_DONE_THRESH);
>>  	writel(0x0, priv->mac_reg + TDMA_FLOW_PERIOD);
>>  	writel((TX_DESCS << DMA_RING_SIZE_SHIFT) | RX_BUF_LENGTH,
>> @@ -469,8 +470,6 @@ static int bcmgenet_gmac_eth_start(struct udevice *dev)
>>  
>>  	priv->tx_desc_base = priv->mac_reg + GENET_TX_OFF;
>>  	priv->rx_desc_base = priv->mac_reg + GENET_RX_OFF;
>> -	priv->tx_index = 0x0;
>> -	priv->rx_index = 0x0;
>>  
>>  	bcmgenet_umac_reset(priv);
>>  
>>