Re: [PATCH RESEND V4 2/9] mailbox: Add NVIDIA Tegra XUSB mailbox driver

[Andrew Bresticker]

>> +     for (i = 0; i < ARRAY_SIZE(mbox->vchan_allocated); i++) {
>> +             if (mbox->vchan_allocated[i])
>> +                     mbox_chan_received_data(&mbox->mbox.chans[i], &msg);
>> +     }
>
> It seems like the only reason why you need to explicitly check for an
> allocated channel is that mbox_chan_received_data() would otherwise
> crash. Are mailbox drivers really supposed to keep track of whether a
> channel has been requested by a client? Isn't that something that should
> be done in the core?

Yeah, I'd agree that this is something that should be handled by the core.

>> +static int tegra_xusb_mbox_probe(struct platform_device *pdev)
>> +{
>> +     struct tegra_xusb_mbox *mbox;
>> +     struct resource *res;
>> +     int ret;
>> +
>> +     mbox = devm_kzalloc(&pdev->dev, sizeof(*mbox), GFP_KERNEL);
>> +     if (!mbox)
>> +             return -ENOMEM;
>> +     platform_set_drvdata(pdev, mbox);
>> +     spin_lock_init(&mbox->lock);
>> +
>> +     mbox->mbox.dev = &pdev->dev;
>> +     mbox->mbox.chans = devm_kcalloc(&pdev->dev, TEGRA_XUSB_MBOX_NUM_CHANS,
>> +                                     sizeof(*mbox->mbox.chans), GFP_KERNEL);
>> +     if (!mbox->mbox.chans)
>> +             return -ENOMEM;
>> +     mbox->mbox.num_chans = TEGRA_XUSB_MBOX_NUM_CHANS;
>> +     mbox->mbox.ops = &tegra_xusb_mbox_chan_ops;
>> +     mbox->mbox.txdone_poll = true;
>> +     mbox->mbox.txpoll_period = 0; /* no need to actually poll */
>
> Does the core perhaps need special handling for this? It seems like
> poll_txdone() will always rearm the timer used to do the polling,
> irrespective of whether the transfer is actually done or not.

Yeah, that doesn't seem quite right...

> Maybe something like this patch would be more correct in handling
> this:
>
> diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
> index afcb430508ec..85691a7d8ca6 100644
> --- a/drivers/mailbox/mailbox.c
> +++ b/drivers/mailbox/mailbox.c
> @@ -117,10 +117,11 @@ static void poll_txdone(unsigned long data)
>                 struct mbox_chan *chan = &mbox->chans[i];
>
>                 if (chan->active_req && chan->cl) {
> -                       resched = true;
>                         txdone = chan->mbox->ops->last_tx_done(chan);
>                         if (txdone)
>                                 tx_tick(chan, 0);
> +                       else
> +                               resched = true;
>                 }
>         }

... but we still need to re-arm the timer if tx_tick() submits another
message.  Perhaps the better thing to do is to have msg_submit() arm
the timer.

>> +     res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>> +     if (!res)
>> +             return -ENODEV;
>> +     mbox->regs = devm_ioremap(&pdev->dev, res->start, resource_size(res));
>> +     if (!mbox->regs)
>> +             return -ENOMEM;
>
> This doesn't look right. Upon closer inspection, the reason why you
> don't use devm_request_resource() is because these registers are shared
> with the XHCI controller.
>
> Perhaps a better design would be for the XHCI driver to expose the
> mailbox rather than split it off into a separate driver.

Well that's what I had originally, but then it was suggested I make it
a separate driver.

Stephen also brought this up during review and suggested that some
sort of MFD would be the best way to structure this, but was fine with
the way I have it now.  I can move this driver around (again) if you
feel that strongly about it...

>> diff --git a/include/soc/tegra/xusb.h b/include/soc/tegra/xusb.h
>> new file mode 100644
>> index 0000000..cfe211d
>> --- /dev/null
>> +++ b/include/soc/tegra/xusb.h
>
> Perhaps this should really be named xusb-mbox.h?

I'd prefer to leave it as xusb.h so that any other XUSB-related
definitions can be left here.
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