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

On Tue, Jul 21, 2015 at 11:18 PM, Lee Jones [off-list ref] wrote:

On Tue, 21 Jul 2015, Jassi Brar wrote:

quoted

On Tue, Jul 21, 2015 at 9:22 PM, Lee Jones [off-list ref] wrote:

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On Tue, 21 Jul 2015, Jassi Brar wrote:

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+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 :)

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+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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