Re: [PATCH 2/3 v8] mailbox: Enable BCM2835 mailbox support

[Noralf TrÃnnes]

Den 08.05.2015 10:33, skrev Alexander Stein:
> On Thursday 07 May 2015, 12:54:20 wrote Eric Anholt:
> > Noralf TrÃnnes <noralf@xxxxxxxxxxx> writes:
> >
> > > Den 05.05.2015 22:27, skrev Eric Anholt:
> > > > From: Lubomir Rintel <lkundrak@xxxxx>
> > > >
> > > > This mailbox driver provides a single mailbox channel to write 32-bit
> > > > values to the VPU and get a 32-bit response.  The Raspberry Pi
> > > > firmware uses this mailbox channel to implement firmware calls, while
> > > > Roku 2 (despite being derived from the same firmware tree) doesn't.
> > > >
> > > > The driver was originally submitted by Lubomir, based on the
> > > > out-of-tree 2708 mailbox driver.  Eric Anholt fixed it up for
> > > > upstreaming, with the major functional change being that it now has no
> > > > notion of multiple channels (since that is a firmware-dependent
> > > > concept) and instead the raspberrypi-firmware driver will do that
> > > > bit-twiddling in its own messages.
> > > ...
> > > > +static struct platform_driver bcm2835_mbox_driver = {
> > > > +	.driver = {
> > > > +		.name = "bcm2835-mbox",
> > > > +		.owner = THIS_MODULE,
> > > > +		.of_match_table = bcm2835_mbox_of_match,
> > > > +	},
> > > > +	.probe		= bcm2835_mbox_probe,
> > > > +	.remove		= bcm2835_mbox_remove,
> > > > +};
> > > > +module_platform_driver(bcm2835_mbox_driver);
> > > I have tested this driver and the firmware driver booting directly
> > > from the VideoCore bootloader (no uboot).
> > > The mailbox driver loads too late to turn on USB power:
> > Yeah, I have a patch on my branches that returns -EPROBE_DEFER when
> > trying to get a power domain and not finding the provider.  It was
> > rejected by the maintainers in favor of a proposed solution whose
> > description I didn't quite follow.
> Do you have a link for this thread?
>
> > > This silences the warning:
> > > struct raspberrypi_power_domain raspberrypi_power_domain_usb = {
> > >       .base = {
> > >           .power_on_latency_ns = 600000000,
> > Oh, nice.  Thanks!
> Well, Using a timeout for dependencies seems odd to me.

I can only find one place where power_on_latency_ns is set,
arch/arm/mach-imx/gpc.c:
static struct pu_domain imx6q_pu_domain = {
    .base = {
        .name = "PU",
        .power_off = imx6q_pm_pu_power_off,
        .power_on = imx6q_pm_pu_power_on,
        .power_off_latency_ns = 25000,
        .power_on_latency_ns = 2000000,
    },
};

power_on_latency_ns is not set by the core, so it defaults to zero.
So in the default case, genpd_power_on() will always issue a warning on
the first power on.

I would say that power_on_latency_ns is a characteristic of the power
domain, like enable_time for regulators.


Noralf.

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