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SubjectRe: [PATCH 1/3] mailbox: sprd: Introduce refcnt when clients requests/free channels
On Mon, Feb 08, 2021 at 10:06:47PM +0800, Baolin Wang wrote:
> Hi Orson,
>
> On Mon, Feb 8, 2021 at 7:52 PM Orson Zhai <orsonzhai@gmail.com> wrote:
> >
> > From: Orson Zhai <orson.zhai@unisoc.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@unisoc.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.

Yes, atomic could make refcnt itself safe. But mutex lock is to make whole processing of
reading/writing registers safe.

Consider case like this:

channel #1 channel #2
-------------------------------------
startup
.....
shutdown startup
|-refcnt==0 |
| |-retcnt+1
| |-enable mailbox
|-disable mailbox

Mailbox will be wrongly disabled after client requests channel #2's startup.

>
> >
> > 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.

Right, will remove at next version.

Thanks for reviewing!

-Orson

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