linux-kernel - Re: GPIO support for HTC Dream

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Date:	Mon, 14 Dec 2009 22:40:19 -0800
From:	Arve Hjønnevåg <arve@...roid.com>
To:	H Hartley Sweeten <hartleys@...ionengravers.com>
Cc:	Daniel Walker <dwalker@...eaurora.org>,
	Pavel Machek <pavel@....cz>,
	Ryan Mallon <ryan@...ewatersys.com>,
	Iliyan Malchev <malchev@...gle.com>,
	Brian Swetland <swetland@...gle.com>,
	kernel list <linux-kernel@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: GPIO support for HTC Dream

On Mon, Dec 14, 2009 at 10:12 AM, H Hartley Sweeten
<hartleys@...ionengravers.com> wrote:
> On Monday, December 14, 2009 10:55 AM, Daniel Walker wrote:
>> On Mon, 2009-12-14 at 07:45 +0100, Pavel Machek wrote:
>>> Hi!
>>>
>>>> This looks MUCH better!
>>>
>>> Thanks :-).
>>>
>>>>> arch/arm/Kconfig                     |    1
>>>>> arch/arm/mach-msm/board-dream-gpio.c |  327 +++++++++--------------------------
>>> ...
>>>> Please update (or remove) this diffstat.  It no longer matches the patch.
>>>
>>> I was just showing differences to _previous_ version, not what I was sending.
>>>
>>>> Ok.  The hardware still seems a bit strange. Is there any datasheet
>>>> available?
>>>
>>> I don't think there is one. Daniel, can you help here?
>>
>> I don't know if there is one or not (I'd guess not).. I can't release
>> documents, but I could try to address specific questions or find people
>> to answer specific questions.
>
> Hello Daniel,
>
> My specific question was about the gpio hardware registers.
>
> From Pavel's implementation it appears that the gpio's are organized as a
> number of 8-bit ports.  Each of these ports only have one 8-bit register.
> Writing a '1' to a bit in the register makes the associated pin a high-level
> output.  Writing a '0' makes the pin a low-level output or an input pin.
> Reading the port at this point will return the actual 'input' level of the pin.
>
> The hardware seems a bit strange and I just wanted to verify that this is
> correct.  If it is, this would explain the need to keep the 'shadow' contents
> of the port in order to set the 'direction' of a pin.
>
> I was also wondering if the initial 'shadow' value needs to be written to the
> port at init in order to correctly establish the output value for specific
> pins.
>
> One other thing.  Are the gpio's handled by Pavel's driver actually from the
> MSM chip or from an external CPLD?  The registers are all defined as:
>
> +               .reg = reg_num + DREAM_CPLD_BASE,
>
> If they are external from the MSM chip this driver should probably be renamed
> to something more appropriate since it is probably dream specific and not
> generic to the msm architecture.

These are board specific gpios. I think it would be less confusing if
the msm gpio support was added first.

-- 
Arve Hjønnevåg
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