linux-kernel - Re: [PATCH v2 2/9] mailbox: Add NVIDIA Tegra XUSB mailbox driver

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Date:	Wed, 27 Aug 2014 11:13:47 -0700
From:	Andrew Bresticker <abrestic@...omium.org>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Jassi Brar <jassisinghbrar@...il.com>,
	Thierry Reding <thierry.reding@...il.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Linus Walleij <linus.walleij@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mathias Nyman <mathias.nyman@...el.com>,
	Grant Likely <grant.likely@...aro.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Arnd Bergmann <arnd@...db.de>,
	Kishon Vijay Abraham I <kishon@...com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: [PATCH v2 2/9] mailbox: Add NVIDIA Tegra XUSB mailbox driver

On Wed, Aug 27, 2014 at 10:50 AM, Stephen Warren <swarren@...dotorg.org> wrote:
> On 08/27/2014 11:38 AM, Andrew Bresticker wrote:
>>
>> On Mon, Aug 25, 2014 at 12:01 PM, Stephen Warren <swarren@...dotorg.org>
>> wrote:
>>>
>>> On 08/18/2014 11:08 AM, Andrew Bresticker wrote:
>>>>
>>>> +static int tegra_xusb_mbox_probe(struct platform_device *pdev)
>>>
>>>
>>>
>>>> +       res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>>>>
>>>> +       if (!res)
>>>> +               return -ENODEV;
>>>
>>>
>>>
>>> Should devm_request_mem_region() be called here to claim the region?
>>
>>
>> No, the xHCI host driver also needs to map these registers, so they
>> cannot be mapped exclusively here.
>
>
> That's unfortunate. Having multiple drivers with overlapping register
> regions is not a good idea. Can we instead have a top-level driver map all
> the IO regions, then instantiate the various different sub-components
> internally, and divide up the address space. Probably via MFD or similar.
> That would prevent multiple drivers from touching the same register region.

Perhaps I'm misunderstanding, but I don't see how MFD would prevent us
from having to map this register space in two different locations -
the XUSB FPCI address space cannot be divided cleanly between host and
mailbox registers.  Or are you saying that there should be a separate
device driver that exposes an API for accessing this register space,
like the Tegra fuse or PMC drivers?
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