[PATCH v5 2/7] mailbox: arm_mhu: add driver for ARM MHU controller

[arnd@arndb.de (Arnd Bergmann)]

On Tuesday 03 February 2015 14:46:11 Russell King - ARM Linux wrote:
> On Tue, Feb 03, 2015 at 08:09:34PM +0530, Jassi Brar wrote:
> > On 3 February 2015 at 18:02, Russell King - ARM Linux
> > <linux@arm.linux.org.uk> wrote:
> > > On Tue, Feb 03, 2015 at 05:29:23PM +0800, Vincent Yang wrote:
> > >> +static int mhu_send_data(struct mbox_chan *chan, void *data)
> > >> +{
> > >> +     struct mhu_link *mlink = chan->con_priv;
> > >> +
> > >> +     pr_debug("%s:%d\n", __func__, __LINE__);
> > >> +     if (!mhu_last_tx_done(chan)) {
> > >> +             dev_err(chan->mbox->dev, "Last TX(%d) pending!\n", mlink->irq);
> > >> +             return -EBUSY;
> > >> +     }
> > >> +
> > >> +     writel_relaxed((u32)data, mlink->tx_reg + INTR_SET_OFS);
> > >
> > > Doesn't that cause a GCC warning?
> > >
> > I don't see any, but I'll drop the cast.
> 
> A cast is probably needed.  You're right that GCC no longer warns about
> this - I'm pretty sure it used to complain about casting pointers to
> ints, and we used to need to cast to "unsigned long" first.

It definitely warns about converting an u64 to pointer or back,
and it warns on 64-bit machines about this conversion.

On a related note, I wonder why the driver actually converts a pointer to
int. I believe we have discussed this in the past but don't remember the
outcome. I had expected to see here something like:

static int mhu_send_data(struct mbox_chan *chan, void *data)
{
	struct mhu_link *mlink = chan->con_priv;
	u32 *arg = data;

	writel_relaxed(*arg, mlink->tx_reg + INTR_SET_OFS);
}

i.e. dereferencing the pointer instead of using the actual value.

	Arnd