netdev - Re: [net v3 PATCH 1/1] net: mvpp2: clear BM pool before initialization

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Message-ID: <20240118155053.6c1bc52a@device-28.home>
Date: Thu, 18 Jan 2024 15:50:53 +0100
From: Maxime Chevallier <maxime.chevallier@...tlin.com>
To: Jenishkumar Maheshbhai Patel <jpatel2@...vell.com>
Cc: <marcin.s.wojtas@...il.com>, <linux@...linux.org.uk>,
 <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
 <pabeni@...hat.com>, <netdev@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, Antoine Tenart <atenart@...nel.org>
Subject: Re: [net v3 PATCH 1/1] net: mvpp2: clear BM pool before
 initialization

Hello,

On Thu, 18 Jan 2024 00:14:47 -0800
Jenishkumar Maheshbhai Patel <jpatel2@...vell.com> wrote:

> Register value persist after booting the kernel using
> kexec which results in kernel panic. Thus clear the
> BM pool registers before initialisation to fix the issue.

[...]

> +/* Cleanup pool before actual initialization in the OS */
> +static void mvpp2_bm_pool_cleanup(struct mvpp2 *priv, int pool_id)
> +{
> +	u32 val;
> +	int i;
> +	unsigned int thread = mvpp2_cpu_to_thread(priv, get_cpu());

Please sort these lines with the longest line at the top, following the
reverse christmas-tree style.

> +
> +	/* Drain the BM from all possible residues left by firmware */
> +	for (i = 0; i < MVPP2_BM_POOL_SIZE_MAX; i++)
> +		mvpp2_thread_read(priv, thread, MVPP2_BM_PHY_ALLOC_REG(pool_id));

Since you don't need to use the thread-based accessors after this, you
can call put_cpu() right now to avoid keeping preemption disabled
unnecessarily for too long.

> +	/* Stop the BM pool */
> +	val = mvpp2_read(priv, MVPP2_BM_POOL_CTRL_REG(pool_id));
> +	val |= MVPP2_BM_STOP_MASK;
> +	mvpp2_write(priv, MVPP2_BM_POOL_CTRL_REG(pool_id), val);
> +
> +	/* Mask BM all interrupts */
> +	mvpp2_write(priv, MVPP2_BM_INTR_MASK_REG(pool_id), 0);
> +
> +	/* Clear BM cause register */
> +	mvpp2_write(priv, MVPP2_BM_INTR_CAUSE_REG(pool_id), 0);

These two registers dealing with interrupt masking and cause are
already cleared in mvpp2_bm_init(), not shown in the diff context, so
either you can remove these or the ones in mvpp2_bm_init().

> +	put_cpu();
> +}
> +
>  static int mvpp2_bm_init(struct device *dev, struct mvpp2 *priv)
>  {
>  	enum dma_data_direction dma_dir = DMA_FROM_DEVICE;
>  	int i, err, poolnum = MVPP2_BM_POOLS_NUM;
>  	struct mvpp2_port *port;
>  
> +	if (priv->percpu_pools)
> +		poolnum = mvpp2_get_nrxqs(priv) * 2;
> +
> +	/* Clean up the pool state in case it contains stale state */
> +	for (i = 0; i < poolnum; i++)
> +		mvpp2_bm_pool_cleanup(priv, i);
> +
>  	if (priv->percpu_pools) {
>  		for (i = 0; i < priv->port_count; i++) {
>  			port = priv->port_list[i];
> @@ -629,7 +661,6 @@ static int mvpp2_bm_init(struct device *dev, struct mvpp2 *priv)
>  			}
>  		}
>  
> -		poolnum = mvpp2_get_nrxqs(priv) * 2;
>  		for (i = 0; i < poolnum; i++) {
>  			/* the pool in use */
>  			int pn = i / (poolnum / 2);

Thanks,

Maxime