RE: [PATCH net v5 1/4] net: ethernet: oa_tc6: Interrupt is active low, level triggered.

[Selvamani Rajagopal]

> -----Original Message-----
> From: Parthiban.Veerasooran@xxxxxxxxxxxxx <Parthiban.Veerasooran@xxxxxxxxxxxxx>
> Subject: Re: [PATCH net v5 1/4] net: ethernet: oa_tc6: Interrupt is active low, level triggered.
> 
> 
> With your above patches, I did a quick test (Test case 2) with two
> Microchip MAC-PHYs and faced a similar issue reported before. Sharing
> the dmesg crash log for your reference.

Root cause seems to be same. When oa_tc6_update_rx_skb function is called, tc6->rx_skb 
seems to be NULL, which may mean, controller seems to be not getting start

I have a theory. Look at line #933. We have the following comment. I am sure this could be true
for the call to oa_tc6_prcs_rx_frame_end at line #926 or oa_tc6_prcs_ongoing_rx_frame at line #950.
               /* After rx buffer overflow error received, there might be a
                 * possibility of getting an end valid of a previously
                 * incomplete rx frame along with the new rx frame start valid.
                 */

Either we change the following line in the function oa_tc6_update_rx_skb
    if ((tc6->rx_skb->tail + length) > tc6->rx_skb->end) {
to
        if (tc6->rx_skb == NULL || (tc6->rx_skb->tail + length) > tc6->rx_skb->end) {

Or add a check 
   If (tc6->rx_skb) before calling above mentioned two functions from the callee function.

I could do. But I have no way of verifying this. I am sure it will fix the crash. I would like to confirm
whether traffic recovers.

> 
> [ 2863.182105] eth1: Receive buffer overflow error
> [ 2863.199905] eth1: Receive buffer overflow error
> [ 2867.669312] Unable to handle kernel NULL pointer dereference at
> virtual address 00000000000000b8