linux-kernel - Re: [PATCH 3/6] mailbox: Add support for ST's Mailbox IP

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Date:	Tue, 21 Jul 2015 21:39:04 +0530
From:	Jassi Brar <jassisinghbrar@...il.com>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	kernel@...inux.com, Devicetree List <devicetree@...r.kernel.org>
Subject: Re: [PATCH 3/6] mailbox: Add support for ST's Mailbox IP

On Tue, Jul 21, 2015 at 9:22 PM, Lee Jones <lee.jones@...aro.org> wrote:
> On Tue, 21 Jul 2015, Jassi Brar wrote:
>
>> >
>> >> > +static int sti_mbox_send_data(struct mbox_chan *chan, void *data)
>> >> > +{
>> >> > +       struct sti_channel *chan_info = chan->con_priv;
>> >> > +       struct sti_mbox_device *mdev = chan_info->mdev;
>> >> > +       struct sti_mbox_pdata *pdata = dev_get_platdata(mdev->dev);
>> >> > +       unsigned int instance = chan_info->instance;
>> >> > +       unsigned int channel = chan_info->channel;
>> >> > +       void __iomem *base;
>> >> > +
>> >> > +       if (!sti_mbox_tx_is_ready(chan))
>> >> > +               return -EBUSY;
>> >> This is the first thing I look out for in every new driver :)  this
>> >> check is unnecessary.
>> >
>> > In what way?  What if the channel is disabled or there is an IRQ
>> > already pending?
>> >
>> API calls send_data() only if last_tx_done() returned true.
>
> I know for a fact that the 'catchers' in sti_mbox_tx_is_ready() to
> fire, because I have triggered them.  I'd really rather keep this
> harmless check in.
>
If you put some printk in send_data() and last_tx_done() you'll see
what I mean :)

>> >> > +static const struct sti_mbox_pdata mbox_stih407_pdata = {
>> >> > +       .num_inst       = 4,
>> >> > +       .num_chan       = 32,
>> >> > +       .irq_val        = 0x04,
>> >> > +       .irq_set        = 0x24,
>> >> > +       .irq_clr        = 0x44,
>> >> > +       .ena_val        = 0x64,
>> >> > +       .ena_set        = 0x84,
>> >> > +       .ena_clr        = 0xa4,
>> >> >
>> >> Register offsets are parameters of the controller
>> >
>> > And this is a controller driver?  Not sure I get the point.
>> >
>> Platform_data usually carries board/platform specific parameters.
>> Register offset "properties" are as fixed as the behavior of the
>> controller, so they should stay inside the code, not come via
>> platform_data.
>
> That's not the case for this controller.  There is nothing preventing
> these values from changing on a new board revisions.
>
Hmm ... interesting! Can't see how enable/disable channel and irq
set/clear could be effected by writing to random, but agreed upon,
location between two processors. There ought to be some controller
listening there?  Now I am more interested in knowing this IP :)

thnx.
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