linux-kernel - Re: [PATCH 4/9] PCI: mvebu: add support for reset on GPIO

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Date:	Tue, 13 Aug 2013 11:19:01 +0200
From:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
To:	Kumar Gala <galak@...eaurora.org>
CC:	Russell King <linux@....linux.org.uk>,
	Jason Cooper <jason@...edaemon.net>,
	Andrew Lunn <andrew@...n.ch>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-pci@...r.kernel.org, Rob Herring <rob.herring@...xeda.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Ian Campbell <ian.campbell@...rix.com>
Subject: Re: [PATCH 4/9] PCI: mvebu: add support for reset on GPIO

[Added DT maintainers directly for a question below]

On 08/13/13 02:56, Kumar Gala wrote:
> On Aug 12, 2013, at 1:46 PM, Sebastian Hesselbarth wrote:
>
>> This patch adds a check for DT passed reset-gpios property and deasserts/
>> asserts reset pin on probe/remove with configurable delay. Corresponding
>> binding documentation is also updated.
>>
>> Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
[...]
>> diff --git a/Documentation/devicetree/bindings/pci/mvebu-pci.txt b/Documentation/devicetree/bindings/pci/mvebu-pci.txt
>> index 638673a..f2fa261 100644
>> --- a/Documentation/devicetree/bindings/pci/mvebu-pci.txt
>> +++ b/Documentation/devicetree/bindings/pci/mvebu-pci.txt
>> @@ -76,6 +76,8 @@ and the following optional properties:
>> - marvell,pcie-lane: the physical PCIe lane number, for ports having
>>    multiple lanes. If this property is not found, we assume that the
>>    value is 0.
>> +- reset-gpios: optional gpio to PERST#
>> +- reset-delay-ms: delay in ms to wait after reset de-assertion
>
> Both of these should probably be marvell,reset...

Kumar,

as Thomas already mentioned, non-prefixed "foo-gpios" are quite common.
As reset gpios are likely to be common among SoC pci controller setups,
I though I'd stick with the non-prefixed property. But I have no strong
opinion about it - but let's see how DT jurisdiction will vote :)

> Does reset-delay-ms vary per board? I can't remember where the
discussion got to about configuration info.

Hmm, for Dove SoC, I only have one board to test - but the driver
currently is for 4 different SoCs. I just did some quick evaluation
of the reset delay required to bring up the device on the D3Plug.
Using 10ms was too short, 20ms worked.

I guess there will be other SoC/boards requiring different delays
but I am fine with hardcoded 20ms and re-introduce reset-delay property
only if it is really required. The driver's default is 20ms anyway.

>>
>> Example:
>
> It's usually good to update example to show all optional properties.

Ok, will add the properties to one of the example ports.

Thanks,

Sebastian

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