From: Simon Glass <sjg@chromium.org>
To: Stephen Warren <swarren@wwwdotorg.org>
Cc: Devicetree Discuss <devicetree-discuss@lists.ozlabs.org>,
U-Boot Mailing List <u-boot@lists.denx.de>,
Jerry Van Baren <vanbaren@cideas.com>,
Sean Paul <seanpaul@chromium.org>, Tom Rini <trini@ti.com>
Subject: Re: [PATCH 09/14] fdt: Add polarity-aware gpio functions to fdtdec
Date: Thu, 15 Nov 2012 15:31:49 -0800 [thread overview]
Message-ID: <CAPnjgZ0qt200WSzmYXXCiEZ6d_d8mxVs1MU-byA7-JDM_JR4rQ@mail.gmail.com> (raw)
In-Reply-To: <5091FF8B.7040109@wwwdotorg.org>
Hi Stephen,
On Wed, Oct 31, 2012 at 9:50 PM, Stephen Warren <swarren@wwwdotorg.org> wrote:
> On 10/31/2012 05:59 PM, Simon Glass wrote:
>> Hi,
>>
>> On Fri, Oct 26, 2012 at 12:17 AM, Lucas Stach <dev@lynxeye.de> wrote:
>>> Am Donnerstag, den 25.10.2012, 19:31 -0700 schrieb Simon Glass:
>>>> From: Sean Paul <seanpaul@chromium.org>
>>>>
>>>> Add get and set gpio functions to fdtdec that take into account the
>>>> polarity field in fdtdec_gpio_state.flags.
>>>>
>>> In another thread Stephen Warren and I came to the conclusion that we
>>> most likely should remove this polarity flag from the GPIO bindings.
>>>
>>> Currently it is only for the USB VBUS GPIO which should move over to
>>> regulators once they land in U-Boot. Do you have any other applications
>>> for this flag, so we might reconsider removing it?
>>>
>>
>> Well, any time you have a flag which is inverted in meaning, it can be
>> useful. We have several switches on the board which can be active high
>> or low, and polarity is used for that.
>>
>> In fact, it would be nice IMO to be able to specify input/output as
>> well. I know the exynos bindings do this. There is a noddy function
>> called fdtdec_setup_gpio() in U-Boot which really needs to be sorted
>> out. I discussed with Stephen some time ago how GPIOs should be
>> SOC-specific and it should be possible to set up a GPIO with a single
>> call, as Linux does. The more information there is in the binding, the
>> more it can do automatically.
>>
>> Does the Tegra Linux GPIO binding still have a polarity?
>
> Yes it does, although in practice it can't be used (and hence should
> really be removed), since not all GPIO bindings have such a flag, so
> there is always a need for a separate property to indicate the polarity
> (c.f. fixed-regulator with GPIO control bindings for example).
>
I've had a bit of time to look into this. I see that the regulator
framework in the kernel seems to be used for various control purposes,
and provides useful polarity stuff. I was rather hoping that GPIOs
could be a bit more high level in U-Boot, with information about:
- input/output
- drive strength
- polarity
- pull up/down
In fact most of these are actually supported in most kernel bindings,
but of course it is binding-specific. Would it be useful to ask for a
polarity setting in the GPIO. When it is not available, the polarity
would then always be normal.
This might avoid moving polarity and input/output selecting down into
each client of the gpio, which seems undesirable in general.
Should we consider a second level of indirection for GPIOs to support
these non-binding features? It seems a bit complicated though.
However, if it is too late to do this, or not desirable for some
reason, then we should just drop this patch.
Regards,
Simon
next prev parent reply other threads:[~2012-11-15 23:31 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-26 2:30 [PATCH 0/14] fdt: Add various device tree utilities and features Simon Glass
[not found] ` <1351218671-15228-1-git-send-email-sjg-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
2012-10-26 2:30 ` [PATCH 01/14] fdt: Add function to get config int from device tree Simon Glass
2012-10-26 2:30 ` [PATCH 02/14] fdt: Add function to get a config string " Simon Glass
2012-10-26 2:31 ` [PATCH 03/14] fdt: Add fdtdec_decode_region() to decode memory region Simon Glass
2012-10-26 2:31 ` [PATCH 04/14] fdt: Add function for decoding multiple gpios globally available Simon Glass
2012-10-26 2:31 ` [PATCH 05/14] fdt: Export fdtdec_find_alias_node() function Simon Glass
[not found] ` <1351218671-15228-6-git-send-email-sjg-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
2012-10-26 4:24 ` David Gibson
2012-10-31 23:50 ` Simon Glass
2012-10-26 2:31 ` [PATCH 06/14] fdt: Export fdtdec_lookup() and fix the name Simon Glass
2012-10-26 2:31 ` [PATCH 07/14] fdt: Add function to read boolean property Simon Glass
2012-10-26 2:31 ` [PATCH 08/14] fdt: Add fdtdec_get_uint64 to decode a 64-bit value from a property Simon Glass
2012-10-26 2:31 ` [PATCH 09/14] fdt: Add polarity-aware gpio functions to fdtdec Simon Glass
2012-10-26 7:17 ` Lucas Stach
2012-10-31 23:59 ` Simon Glass
2012-11-01 4:50 ` Stephen Warren
2012-11-15 23:31 ` Simon Glass [this message]
2012-11-15 23:46 ` Stephen Warren
2012-11-16 0:01 ` Simon Glass
2012-10-26 2:31 ` [PATCH 11/14] fdt: Tell the FDT library where the device tree is Simon Glass
2012-10-26 2:31 ` [PATCH 12/14] fdt: Allow device tree to specify secure booting Simon Glass
2012-10-26 2:31 ` [PATCH 10/14] fdt: Load boot command from device tree Simon Glass
2012-10-26 2:31 ` [PATCH 13/14] fdt: Add option to default to most compatible conf in a fit image Simon Glass
2012-10-26 2:31 ` [PATCH 14/14] fdt: Set kernaddr if fdt indicates a kernel is present Simon Glass
[not found] ` <1351218671-15228-15-git-send-email-sjg-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
2012-11-28 14:30 ` [U-Boot] " Dennis Lan (dlan)
2012-11-18 1:35 ` [PATCH 0/14] fdt: Add various device tree utilities and features Jerry Van Baren
2012-11-19 17:08 ` Simon Glass
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