Re: [PATCH v2 RFC net-next 09/18] net: mvpp2: add FCA RXQ non occupied descriptor threshold

Russell King - ARM Linux admin
2021-01-24T13:02:43Z

On Sun, Jan 24, 2021 at 01:43:58PM +0200, stefanc@marvell.com wrote:
> diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> index 9d69752..0f5069f 100644
> --- a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> +++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> @@ -1154,6 +1154,9 @@ static void mvpp2_interrupts_mask(void *arg)
> mvpp2_thread_write(port->priv,
> mvpp2_cpu_to_thread(port->priv, smp_processor_id()),
> MVPP2_ISR_RX_TX_MASK_REG(port->id), 0);
> + mvpp2_thread_write(port->priv,
> + mvpp2_cpu_to_thread(port->priv, smp_processor_id()),
> + MVPP2_ISR_RX_ERR_CAUSE_REG(port->id), 0);

I wonder if this should be refactored:

u32 thread = mvpp2_cpu_to_thread(port->priv, smp_processor_id());

mvpp2_thread_write(port->priv, thread,
MVPP2_ISR_RX_TX_MASK_REG(port->id), 0);
mvpp2_thread_write(port->priv, thread,
MVPP2_ISR_RX_ERR_CAUSE_REG(port->id), 0);

to avoid having to recompute mvpp2_cpu_to_thread() for each write?

However, looking deeper...

static void mvpp2_interrupts_mask(void *arg)
{
struct mvpp2_port *port = arg;
u32 thread;
int cpu;

cpu = smp_processor_id();
if (cpu > port->priv->nthreads)
return

thread = mvpp2_cpu_to_thread(port->priv, cpu);
...

and I wonder about that condition - "cpu > port->priv->nthreads". If
cpu == port->priv->nthreads, then mvpp2_cpu_to_thread() will return
zero, just like the cpu=0 case. This leads me to suspect that this
comparison off by one.

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