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

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Message-ID: <554D1EB1.4070404@tronnes.org>
Date:	Fri, 08 May 2015 22:38:09 +0200
From:	Noralf Trønnes <noralf@...nnes.org>
To:	Alexander Stein <alexanders83@....de>,
	linux-rpi-kernel@...ts.infradead.org
CC:	Eric Anholt <eric@...olt.net>,
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
	Jassi Brar <jassisinghbrar@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3 v8] mailbox: Enable BCM2835 mailbox support


Den 08.05.2015 10:33, skrev Alexander Stein:
> On Thursday 07 May 2015, 12:54:20 wrote Eric Anholt:
>> Noralf Trønnes <noralf@...nnes.org> writes:
>>
>>> Den 05.05.2015 22:27, skrev Eric Anholt:
>>>> From: Lubomir Rintel <lkundrak@...sk>
>>>>
>>>> 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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