From mboxrd@z Thu Jan  1 00:00:00 1970
From: Joe Perches <joe@perches.com>
Subject: Re: [PATCH] can: c_can: Speed up rx_poll function
Date: Mon, 28 Oct 2013 10:12:16 -0700
Message-ID: <1382980336.30941.40.camel@joe-AO722>
References: <1382979582-10352-1-git-send-email-mpa@pengutronix.de>
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Cc: Marc Kleine-Budde <mkl@pengutronix.de>,
	Wolfgang Grandegger <wg@grandegger.com>,
	linux-can@vger.kernel.org, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org, kernel@pengutronix.de
To: Markus Pargmann <mpa@pengutronix.de>
Return-path: <linux-can-owner@vger.kernel.org>
In-Reply-To: <1382979582-10352-1-git-send-email-mpa@pengutronix.de>
Sender: linux-can-owner@vger.kernel.org
List-Id: netdev.vger.kernel.org

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.

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

> +
>  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.