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SubjectRe: [PATCH] can: c_can: Speed up rx_poll function
On Mon, Oct 28, 2013 at 10:12:16AM -0700, Joe Perches wrote:
> On Mon, 2013-10-28 at 17:59 +0100, Markus Pargmann wrote:
> > This patch speeds up the rx_poll function by reducing the number of
> > register reads.
>
> trivial notes:
>
> > diff --git a/drivers/net/can/c_can/c_can.c b/drivers/net/can/c_can/c_can.c
> []
> > @@ -259,6 +259,12 @@ static u32 c_can_read_reg32(struct c_can_priv *priv, enum reg index)
> > +u16 c_can_read_reg16(struct c_can_priv *priv, enum reg index)
> > +{
> > + u16 val = priv->read_reg(priv, index);
> > + return val;
> > +}
>
> This function doesn't seem useful at all.
> It's not exported and it's not static.

Oh right, should be static.

>
> Why not use an in-place priv->read_reg(priv, index)?

No reason for that. Especially with a u16 as mentioned below, it is
clear enough that we have a 16bit value, so I will change it.

>
> > +
> > static void c_can_enable_all_interrupts(struct c_can_priv *priv,
> > int enable)
> > {
> > @@ -798,17 +804,21 @@ static int c_can_do_rx_poll(struct net_device *dev, int quota)
> > u32 num_rx_pkts = 0;
> > unsigned int msg_obj, msg_ctrl_save;
> > struct c_can_priv *priv = netdev_priv(dev);
> > - u32 val = c_can_read_reg32(priv, C_CAN_INTPND1_REG);
> > + unsigned long val = c_can_read_reg16(priv, C_CAN_INTPND1_REG);
>
> Probably better as a u16 as detailed below.
>
> > + /*
> > + * It is faster to read only one 16bit register. This is only possible
> > + * for a maximum number of 16 objects.
> > + */
> > + BUILD_BUG_ON_MSG(C_CAN_MSG_OBJ_RX_LAST > 16,
> > + "Implementation does not support more message objects than 16");
> > +
> > + while (quota > 0 && (val = c_can_read_reg16(priv, C_CAN_INTPND1_REG))) {
> > + msg_obj = 0;
> > + while ((msg_obj = find_next_bit(&val, 16, msg_obj)) < 16 &&
>
> Using ffs instead of find_next_bit would be more standard
> and probably faster too.

I wasn't aware of that. I will change it

Thanks,

Markus Pargmann

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