linux-kernel - Re: [PATCH 1/3] mailbox: sprd: Introduce refcnt when clients requests/free channels

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Message-ID: <CADBw62qiUG2dunB_i1iOp_srkAJP4CrVJX9mU25no++_b10hpg@mail.gmail.com>
Date:   Mon, 8 Feb 2021 22:06:47 +0800
From:   Baolin Wang <baolin.wang7@...il.com>
To:     Orson Zhai <orsonzhai@...il.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Jassi Brar <jassisinghbrar@...il.com>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Devicetree List <devicetree@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Haidong Yao <haidong.yao@...soc.com>,
        Orson Zhai <orson.zhai@...soc.com>
Subject: Re: [PATCH 1/3] mailbox: sprd: Introduce refcnt when clients
 requests/free channels

Hi Orson,

On Mon, Feb 8, 2021 at 7:52 PM Orson Zhai <orsonzhai@...il.com> wrote:
>
> From: Orson Zhai <orson.zhai@...soc.com>
>
> Unisoc mailbox has no way to be enabled/disabled for any single channel.
> They can only be set to startup or shutdown as a whole device at same time.
>
> Add a variable to count references to avoid mailbox FIFO being reset
> unexpectedly when clients are requesting or freeing channels.
>
> Also add a lock to dismiss possible conflicts from register r/w in
> different startup or shutdown threads.
>
> Fixes: ca27fc26cd22 ("mailbox: sprd: Add Spreadtrum mailbox driver")
> Signed-off-by: Orson Zhai <orson.zhai@...soc.com>
> ---
>  drivers/mailbox/sprd-mailbox.c | 38 +++++++++++++++++++++++++-------------
>  1 file changed, 25 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/mailbox/sprd-mailbox.c b/drivers/mailbox/sprd-mailbox.c
> index f6fab24..e606f52 100644
> --- a/drivers/mailbox/sprd-mailbox.c
> +++ b/drivers/mailbox/sprd-mailbox.c
> @@ -60,6 +60,8 @@ struct sprd_mbox_priv {
>         struct clk              *clk;
>         u32                     outbox_fifo_depth;
>
> +       struct mutex            lock;
> +       u32                     refcnt;
>         struct mbox_chan        chan[SPRD_MBOX_CHAN_MAX];
>  };
>
> @@ -215,18 +217,22 @@ static int sprd_mbox_startup(struct mbox_chan *chan)
>         struct sprd_mbox_priv *priv = to_sprd_mbox_priv(chan->mbox);
>         u32 val;
>
> -       /* Select outbox FIFO mode and reset the outbox FIFO status */
> -       writel(0x0, priv->outbox_base + SPRD_MBOX_FIFO_RST);
> +       mutex_lock(&priv->lock);
> +       if (priv->refcnt++ == 0) {
> +               /* Select outbox FIFO mode and reset the outbox FIFO status */
> +               writel(0x0, priv->outbox_base + SPRD_MBOX_FIFO_RST);
>
> -       /* Enable inbox FIFO overflow and delivery interrupt */
> -       val = readl(priv->inbox_base + SPRD_MBOX_IRQ_MSK);
> -       val &= ~(SPRD_INBOX_FIFO_OVERFLOW_IRQ | SPRD_INBOX_FIFO_DELIVER_IRQ);
> -       writel(val, priv->inbox_base + SPRD_MBOX_IRQ_MSK);
> +               /* Enable inbox FIFO overflow and delivery interrupt */
> +               val = readl(priv->inbox_base + SPRD_MBOX_IRQ_MSK);
> +               val &= ~(SPRD_INBOX_FIFO_OVERFLOW_IRQ | SPRD_INBOX_FIFO_DELIVER_IRQ);
> +               writel(val, priv->inbox_base + SPRD_MBOX_IRQ_MSK);
>
> -       /* Enable outbox FIFO not empty interrupt */
> -       val = readl(priv->outbox_base + SPRD_MBOX_IRQ_MSK);
> -       val &= ~SPRD_OUTBOX_FIFO_NOT_EMPTY_IRQ;
> -       writel(val, priv->outbox_base + SPRD_MBOX_IRQ_MSK);
> +               /* Enable outbox FIFO not empty interrupt */
> +               val = readl(priv->outbox_base + SPRD_MBOX_IRQ_MSK);
> +               val &= ~SPRD_OUTBOX_FIFO_NOT_EMPTY_IRQ;
> +               writel(val, priv->outbox_base + SPRD_MBOX_IRQ_MSK);
> +       }
> +       mutex_unlock(&priv->lock);

I think using the atomic_add/sub_and_test() related APIs can remove
the mutex lock.

>
>         return 0;
>  }
> @@ -235,9 +241,13 @@ static void sprd_mbox_shutdown(struct mbox_chan *chan)
>  {
>         struct sprd_mbox_priv *priv = to_sprd_mbox_priv(chan->mbox);
>
> -       /* Disable inbox & outbox interrupt */
> -       writel(SPRD_INBOX_FIFO_IRQ_MASK, priv->inbox_base + SPRD_MBOX_IRQ_MSK);
> -       writel(SPRD_OUTBOX_FIFO_IRQ_MASK, priv->outbox_base + SPRD_MBOX_IRQ_MSK);
> +       mutex_lock(&priv->lock);
> +       if (--priv->refcnt == 0) {
> +               /* Disable inbox & outbox interrupt */
> +               writel(SPRD_INBOX_FIFO_IRQ_MASK, priv->inbox_base + SPRD_MBOX_IRQ_MSK);
> +               writel(SPRD_OUTBOX_FIFO_IRQ_MASK, priv->outbox_base + SPRD_MBOX_IRQ_MSK);
> +       }
> +       mutex_unlock(&priv->lock);
>  }
>
>  static const struct mbox_chan_ops sprd_mbox_ops = {
> @@ -266,6 +276,8 @@ static int sprd_mbox_probe(struct platform_device *pdev)
>                 return -ENOMEM;
>
>         priv->dev = dev;
> +       priv->refcnt = 0;

No need to do this, the priv structure is already cleared to 0.

> +       mutex_init(&priv->lock);
>
>         /*
>          * The Spreadtrum mailbox uses an inbox to send messages to the target
> --
> 2.7.4
>


-- 
Baolin Wang