linux-kernel - Re: [patch 02/12] can: c_can: Fix hardware raminit function

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Date:	Tue, 18 Mar 2014 19:38:52 +0100
From:	Marc Kleine-Budde <mkl@...gutronix.de>
To:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>
CC:	Wolfgang Grandegger <wg@...ndegger.com>,
	Markus Pargmann <mpa@...gutronix.de>,
	Benedikt Spranger <b.spranger@...utronix.de>,
	linux-can@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [patch 02/12] can: c_can: Fix hardware raminit function

On 03/18/2014 06:19 PM, Thomas Gleixner wrote:
> The function is broken in several ways:
> 
>     - The function does not wait for the init to complete.
>       That can take quite some microseconds.
> 
>     - No protection against being called for two chips at the same
>       time. SMP is such a new thing, right?
> 
> Clear the start and the init done bit unconditionally and wait for
> both bits to be clear.
> 
> In the enable path set the init bit and wait
> for the init done bit.
> 
> Add proper locking.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  drivers/net/can/c_can/c_can_platform.c |   48 ++++++++++++++++++++++++++-------
>  1 file changed, 39 insertions(+), 9 deletions(-)
> 
> Index: linux/drivers/net/can/c_can/c_can_platform.c
> ===================================================================
> --- linux.orig/drivers/net/can/c_can/c_can_platform.c
> +++ linux/drivers/net/can/c_can/c_can_platform.c
> @@ -37,8 +37,10 @@
>  
>  #include "c_can.h"
>  
> -#define CAN_RAMINIT_START_MASK(i)	(1 << (i))
> -
> +#define CAN_RAMINIT_START_MASK(i)	(0x001 << (i))
> +#define CAN_RAMINIT_DONE_MASK(i)	(0x100 << (i))
> +#define CAN_RAMINIT_ALL_MASK(i)		(0x101 << (i))
> +static DEFINE_SPINLOCK(raminit_lock);
>  /*
>   * 16-bit c_can registers can be arranged differently in the memory
>   * architecture of different implementations. For example: 16-bit
> @@ -69,16 +71,44 @@ static void c_can_plat_write_reg_aligned
>  	writew(val, priv->base + 2 * priv->regs[index]);
>  }
>  
> +static void c_can_hw_raminit_wait(const struct c_can_priv *priv, u32 mask,
> +				  u32 val)
> +{
> +	/* We look only at the bits of our instance. */
> +	val &= mask;
> +	while ((readl(priv->raminit_ctrlreg) & mask) != val)
> +		udelay(1);

Do we have to add a timeout here, or is it "safe" to have a potential
endless loop here? As you have probably tortured the hardware and driver
a lot (or have been tortured by them), I assume you would have added a
timeout check if you had seen a lockup here.

> +}
> +
>  static void c_can_hw_raminit(const struct c_can_priv *priv, bool enable)
>  {
> -	u32 val;
> +	u32 mask = CAN_RAMINIT_ALL_MASK(priv->instance);
> +	u32 ctrl;
> +
> +	spin_lock(&raminit_lock);
>  
> -	val = readl(priv->raminit_ctrlreg);
> -	if (enable)
> -		val |= CAN_RAMINIT_START_MASK(priv->instance);
> -	else
> -		val &= ~CAN_RAMINIT_START_MASK(priv->instance);
> -	writel(val, priv->raminit_ctrlreg);
> +	ctrl = readl(priv->raminit_ctrlreg);
> +	/*
> +	 * We clear the done and start bit first. The start bit is
> +	 * looking at the 0 -> transition, but is not self clearing;
> +	 * And we clear the init done bit as well.
> +	 */

nitpick: In the driver/net tree multi line comments look different, the
text starts right after the /*. No need to resend, I'll adjust this
while applying the patch.

> +	ctrl &= ~CAN_RAMINIT_START_MASK(priv->instance);
> +	ctrl |= CAN_RAMINIT_DONE_MASK(priv->instance);
> +	writel(ctrl, priv->raminit_ctrlreg);
> +	ctrl &= ~CAN_RAMINIT_DONE_MASK(priv->instance);
> +	c_can_hw_raminit_wait(priv, ctrl, mask);
> +
> +	if (enable) {
> +		/*
> +		 * Set start bit and wait for the done bit.
> +		 */
> +		ctrl |= CAN_RAMINIT_START_MASK(priv->instance);
> +		writel(ctrl, priv->raminit_ctrlreg);
> +		ctrl |= CAN_RAMINIT_DONE_MASK(priv->instance);
> +		c_can_hw_raminit_wait(priv, ctrl, mask);
> +	}
> +	spin_unlock(&raminit_lock);
>  }
>  
>  static struct platform_device_id c_can_id_table[] = {

Marc

-- 
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