Message-ID: <CABb+yY3==_XJYs=Q8v3fAQbh0SLrgMNP0t048OJroUCcJw0Bgg@mail.gmail.com>
Date:	Wed, 22 Jul 2015 00:06:58 +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 11:18 PM, Lee Jones <lee.jones@...aro.org> wrote:
> On Tue, 21 Jul 2015, Jassi Brar wrote:
>
>> 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 :)
>
> High level
> ----------
>
>           MB0       MB1       MB2       MB3       MB4
>       +---------+---------+---------+---------+---------+
> INST0 |         |         |         |         |         |
>       +---------+---------+---------+---------+---------+
> INST1 |         |         |         |         |         |
>       +---------+---------+---------+---------+---------+
> INST2 |         |         |         |         |         |
>       +---------+---------+---------+---------+---------+
> INST3 |         |         |         |         |         |
>       +---------+---------+---------+---------+---------+
>
> Low level [each box above looks like this)
> ------------------------------------------
>
>          1                                                             32
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> IRQ_VAL | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> IRQ_SET | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> IRQ_CLR | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> ENB_VAL | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> ENB_SET | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> ENB_CLR | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
> That's it.  That's the entirety of the "IP".
>
Thanks for taking time out to draw it. Reading code I did get the idea
that mailbox registers are interleaved rather than usual separate
regions. But that doesn't change anything.
   Regardless of the organisation, the registers do have to be at a
particular address... I mean when you set some bit in ENB_SET
'register' there has to be "something" beneath it that triggers the
interrupt. That "something" is the controller, which can't see such
writes to other locations. Right?  I mean this is just like any other
device controller which may have register space at different offsets
but relative addresses of registers won't change across platforms.

thanks.
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