linux-kernel - Re: [PATCH 2/7] net: ethernet: ti: cpdma: fix desc re-queuing

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Message-ID: <20161202110321.GA1213@khorivan>
Date:   Fri, 2 Dec 2016 13:03:22 +0200
From:   Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>
To:     Grygorii Strashko <grygorii.strashko@...com>
Cc:     "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Mugunthan V N <mugunthanvnm@...com>,
        Sekhar Nori <nsekhar@...com>, linux-kernel@...r.kernel.org,
        linux-omap@...r.kernel.org
Subject: Re: [PATCH 2/7] net: ethernet: ti: cpdma: fix desc re-queuing

On Thu, Dec 01, 2016 at 05:34:27PM -0600, Grygorii Strashko wrote:
> The currently processing cpdma descriptor with EOQ flag set may
> contain two values in Next Descriptor Pointer field:
> - valid pointer: means CPDMA missed addition of new desc in queue;
It shouldn't happen in normal circumstances, right?
So, why it happens only for egress channels? And Does that mean
there is some resynchronization between submit and process function,
or this is h/w issue?

> - null: no more descriptors in queue.
> In the later case, it's not required to write to HDP register, but now
> CPDMA does it.
> 
> Hence, add additional check for Next Descriptor Pointer != null in
> cpdma_chan_process() function before writing in HDP register.
> 
> Signed-off-by: Grygorii Strashko <grygorii.strashko@...com>
> ---
>  drivers/net/ethernet/ti/davinci_cpdma.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/ti/davinci_cpdma.c b/drivers/net/ethernet/ti/davinci_cpdma.c
> index 0924014..379314f 100644
> --- a/drivers/net/ethernet/ti/davinci_cpdma.c
> +++ b/drivers/net/ethernet/ti/davinci_cpdma.c
> @@ -1152,7 +1152,7 @@ static int __cpdma_chan_process(struct cpdma_chan *chan)
>  	chan->count--;
>  	chan->stats.good_dequeue++;
>  
> -	if (status & CPDMA_DESC_EOQ) {
> +	if ((status & CPDMA_DESC_EOQ) && chan->head) {
>  		chan->stats.requeue++;
>  		chan_write(chan, hdp, desc_phys(pool, chan->head));
>  	}
> -- 
> 2.10.1
>