Error on TX descriptor free

DISCUSSION Thomas Petazzoni 2 participants 2 messages Oct 22, 2004 MIPS

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Thomas Petazzoni

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2004-10-22 13:12 UTC #0 lore raw

Hello,

I'm currently using the MV643xx Ethernet driver on my board. When I run the command :

# ifconfig eth0 down

I see the following message :

eth0: Error on Tx descriptor free - could not free 1 descriptors

I went through the code, and saw that this message is displayed in mv64340_eth_free_tx_rings(). This function frees all remaining skbs (registered in the mp->tx_skb array), and decrement mp->tx_ring_skbs. Then, it checks if it reached 0. In my case, it is still 1.

In fact, mp->tx_ring_skbs is initialized to 0 and then incremented in mv64340_eth_start_xmit() (when a transmission starts), and is decremented in mv64340_eth_free_tx_queue (when the transmission is done). But the decrementation only occurs if mp->tx_ring_skbs is different from one. I don't understand why.

At the end of mv64340_eth_free_tx_queue(), the following code makes sure that the number of skbs did not reach 0 :

    if (mp->tx_ring_skbs == 0)
      panic("ERROR - TX outstanding SKBs counter is corrupted");

Well, my question is simply : why can't we decrement the mp->tx_ring_skbs counter to 0 ?

What needs to be fixed ? The decrementation of the counter, or the function that frees the TX queue when the interface is stopped ?

I've seen similar code in the Titan GE driver.

Do not hesitate to ask for further details,

Thanks,

Thomas

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PETAZZONI Thomas - [email protected]
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Manish Lachwani

2004-10-22 16:59 UTC #1 lore raw

Hello Thomas

Thats a bug. I dont have a board to try this on. But, can you?

Quoted 14 lines · Thomas Petazzoni

Hello,
I'm currently using the MV643xx Ethernet driver on my board. When I run the command :
# ifconfig eth0 down
I see the following message :
eth0: Error on Tx descriptor free - could not free 1 descriptors
I went through the code, and saw that this message is displayed in mv64340_eth_free_tx_rings(). This function frees all remaining skbs (registered in the mp->tx_skb array), and decrement mp->tx_ring_skbs. Then, it checks if it reached 0. In my case, it is still 1.
In fact, mp->tx_ring_skbs is initialized to 0 and then incremented in mv64340_eth_start_xmit() (when a transmission starts), and is decremented in mv64340_eth_free_tx_queue (when the transmission is done). But the decrementation only occurs if mp->tx_ring_skbs is different from one. I don't understand why.

Quoted 8 lines

At the end of mv64340_eth_free_tx_queue(), the following code makes sure that the number of skbs did not reach 0 :
    if (mp->tx_ring_skbs == 0)
      panic("ERROR - TX outstanding SKBs counter is corrupted");
Well, my question is simply : why can't we decrement the mp->tx_ring_skbs counter to 0 ?
What needs to be fixed ? The decrementation of the counter, or the function that frees the TX queue when the interface is stopped ?

Decrement the counter to zero as you suggested. And remove the panic("..") in mv64340_eth_free_tx_queue(). Let me know if it works fine

Thanks
Manish Lachwani

Quoted 8 lines

I've seen similar code in the Titan GE driver.
Do not hesitate to ask for further details,
Thanks,
Thomas