Subject: Re: [PATCH net v2] gianfar: Fix dma check map error when DMA_API_DEBUG is enabled

From: Claudiu Manoil <[email-masked]>
Date: Thu, 11 Dec 2014 19:05:54 +0200

On 12/11/2014 8:08 AM, Kevin Hao wrote:
> We need to use dma_mapping_error() to check the dma address returned
> by dma_map_single/page(). Otherwise we would get warning like this:
>    WARNING: at lib/dma-debug.c:1140
>    Modules linked in:
>    CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.18.0-rc2-next-20141029 #196
>    task: c0834300 ti: effe6000 task.ti: c0874000
>    NIP: c02b2c98 LR: c02b2c98 CTR: c030abc4
>    REGS: effe7d70 TRAP: 0700   Not tainted  (3.18.0-rc2-next-20141029)
>    MSR: 00021000 <CE,ME>  CR: 22044022  XER: 20000000
>
>    GPR00: c02b2c98 effe7e20 c0834300 00000098 00021000 00000000 c030b898 00000003
>    GPR08: 00000001 00000000 00000001 749eec9d 22044022 1001abe0 00000020 ef278678
>    GPR16: ef278670 ef278668 ef278660 070a8040 c087f99c c08cdc60 00029000 c0840d44
>    GPR24: c08be6e8 c0840000 effe7e78 ef041340 00000600 ef114e10 00000000 c08be6e0
>    NIP [c02b2c98] check_unmap+0x51c/0x9e4
>    LR [c02b2c98] check_unmap+0x51c/0x9e4
>    Call Trace:
>    [effe7e20] [c02b2c98] check_unmap+0x51c/0x9e4 (unreliable)
>    [effe7e70] [c02b31d8] debug_dma_unmap_page+0x78/0x8c
>    [effe7ed0] [c03d1640] gfar_clean_rx_ring+0x208/0x488
>    [effe7f40] [c03d1a9c] gfar_poll_rx_sq+0x3c/0xa8
>    [effe7f60] [c04f8714] net_rx_action+0xc0/0x178
>    [effe7f90] [c00435a0] __do_softirq+0x100/0x1fc
>    [effe7fe0] [c0043958] irq_exit+0xa4/0xc8
>    [effe7ff0] [c000d14c] call_do_irq+0x24/0x3c
>    [c0875e90] [c00048a0] do_IRQ+0x8c/0xf8
>    [c0875eb0] [c000ed10] ret_from_except+0x0/0x18
>
> For TX, we need to unmap the pages which has already been mapped and
> free the skb before return.
>
> For RX, move the dma mapping and error check to gfar_new_skb(). We
> would reuse the original skb in the rx ring when either allocating
> skb failure or dma mapping error.
>
> Signed-off-by: Kevin Hao <[email-masked]>
> ---
> v2: Just update the RX path to reuse the original skb when dma mapping error
>      occurs as suggested by David.
>

Very nice refactoring of gfar_new_skb(), removing gfar_new_rxbdp() in 
the process.  (Did not have the time to test it yet.)
Thanks.

Reviewed-by: Claudiu Manoil <[email-masked]>