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From: Stephen Warren <swarren-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
To: Simon Glass <sjg-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
Cc: U-Boot Mailing List
	<u-boot-0aAXYlwwYIKGBzrmiIFOJg@public.gmane.org>,
	Devicetree Discuss
	<devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org>,
	Tom Warren <TWarren-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>,
	Albert ARIBAUD
	<albert.u.boot-LhW3hqR2+23R7s880joybQ@public.gmane.org>
Subject: Re: [PATCH 02/14] fdt: Add functions to access phandles, arrays and bools
Date: Fri, 02 Dec 2011 08:55:41 -0700	[thread overview]
Message-ID: <4ED8F4FD.4030002@nvidia.com> (raw)
In-Reply-To: <CAPnjgZ29tsNXd1+1eXdTHRjgh_MQJrXoc23_oqO9UPJ73mu7ZA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>

On 12/01/2011 06:01 PM, Simon Glass wrote:
> Hi Stephen,
> 
> On Mon, Nov 28, 2011 at 10:41 AM, Stephen Warren <swarren-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org> wrote:
>> On 11/23/2011 08:54 PM, Simon Glass wrote:
>>> Add a function to lookup a property which is a phandle in a node, and
>>> another to read a fixed-length integer array from an fdt property.
>>> Also add a function to read boolean properties.
>>>
>>> Signed-off-by: Simon Glass <sjg-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>

>>> +/**
>>> + * Look up a boolean property in a node and return it.
>>> + *
>>> + * A boolean properly is true if present in the device tree and false if not
>>> + * present, or present with a 0 value.
>>> + *
>>> + * @param blob       FDT blob
>>> + * @param node       node to examine
>>> + * @param prop_name  name of property to find
>>> + * @return 1 if the properly is present; 0 if it isn't present or is 0
>>> + */
>>> +int fdtdec_get_bool(const void *blob, int node, const char *prop_name);
>>
>> Does U-Boot allow use of the "bool" type here?
> 
> Which bool type? It is returning an int.

I was asking if the return type could be changed to bool.

>>> +int fdtdec_get_bool(const void *blob, int node, const char *prop_name)
>>> +{
>>> +     const s32 *cell;
>>> +     int len;
>>> +
>>> +     debug("%s: %s\n", __func__, prop_name);
>>> +     cell = fdt_getprop(blob, node, prop_name, &len);
>>> +     if (!cell)
>>> +             return 0;
>>> +     if (len >= sizeof(u32) && *cell == 0)
>>> +             return 0;
>>> +
>>> +     return 1;
>>> +}
>>
>> In the kernel, I believe that property existence is all that's usually
>> checked. Is that wrong? Did the definition of a boolean property's value
>> in the function description above come from the specification? If a
>> property had a length of 0/1/2/3 with a zero value, it seems very odd to
>> treat that as true.
> 
> It is useful to be able to set the value to 0 or 1 (with fdtget/put),
> rather than remove or add the property. A value with a length of less
> than one cell is considered illegal here.
> 
> The basic idea is that the presence of the property means that it is
> 'true'. If it happens to have a value, then we allow that to specify
> 'false' if it is zero.

Well, it's more up to standard device tree practice, not me. I've
certainly sent patches that used a property with 0/1 value as a bool
and received review feedback from DT experts that DT represents bools
as present/absent properties, both with no value, so I assume zero
length.

-- 
nvpublic

  parent reply	other threads:[~2011-12-02 15:55 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-11-24  3:54 [PATCH 01/14] fdt: Tidy up a few fdtdec problems Simon Glass
2011-11-24  3:54 ` [PATCH 03/14] arm: fdt: Ensure that an embedded fdt is word-aligned Simon Glass
2011-11-24  3:54 ` [PATCH 06/14] tegra: fdt: Add device tree file for Tegra2 Seaboard Simon Glass
     [not found] ` <1322106896-23054-2-git-send-email-sjg-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
2011-11-24  3:54   ` [PATCH 02/14] fdt: Add functions to access phandles, arrays and bools Simon Glass
     [not found]     ` <1322106896-23054-3-git-send-email-sjg-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
2011-11-28 18:41       ` Stephen Warren
     [not found]         ` <4ED3D5DC.10502-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
2011-11-29  5:12           ` David Gibson
2011-12-02  1:01         ` Simon Glass
     [not found]           ` <CAPnjgZ29tsNXd1+1eXdTHRjgh_MQJrXoc23_oqO9UPJ73mu7ZA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2011-12-02 15:55             ` Stephen Warren [this message]
2011-12-02 16:38               ` Simon Glass
2011-12-02  3:33         ` Jerry Van Baren
2011-12-02  4:58           ` Simon Glass
2011-12-02 17:22             ` Jerry Van Baren
2011-12-02 18:12               ` Simon Glass
2011-11-24  3:54   ` [PATCH 04/14] arm: fdt: Add skeleton device tree file Simon Glass
2011-11-24  3:54   ` [PATCH 05/14] tegra: fdt: Add Tegra2x " Simon Glass
     [not found]     ` <1322106896-23054-6-git-send-email-sjg-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
2011-11-28 18:56       ` Stephen Warren
2011-12-02  1:24         ` Simon Glass
     [not found]           ` <CAPnjgZ11cFm15E9MHXno_YGp0NxdOHhGBavYbQBP5Nu_TOtx7A-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2011-12-02 15:58             ` Stephen Warren
2011-12-02 16:47               ` Simon Glass
2011-11-24  3:54   ` [PATCH 07/14] tegra: fdt: Add initial device tree definitions for USB ports Simon Glass
2011-11-24  3:54   ` [PATCH 14/14] tegra: fdt: Enable FDT support for Seaboard Simon Glass
2011-11-28 18:33   ` [PATCH 01/14] fdt: Tidy up a few fdtdec problems Stephen Warren
     [not found]     ` <4ED3D3F2.8070302-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
2011-11-29  1:10       ` David Gibson
2011-12-01 20:59     ` Simon Glass
     [not found] ` <1322106896-23054-11-git-send-email-sjg@chromium.org>
     [not found]   ` <4ED3DF1D.6080009@nvidia.com>
     [not found]     ` <CAPnjgZ1-yxq-O-vsy1gNJ8AOzh7Sz9j5PG9Tx1sKpnAxhApJAQ@mail.gmail.com>
     [not found]       ` <4EDD38AC.30908@nvidia.com>
     [not found]         ` <CAPnjgZ0MTaPa4pq1VXk_XbmuDyWTfy-H33W4deNVn2ALUrcW_A@mail.gmail.com>
     [not found]           ` <4EDD429E.8010507@nvidia.com>
     [not found]             ` <CAPnjgZ2G220G-i3PPtS4XJYY0ornWFOoK3=b93jG-6GE_g2O5w@mail.gmail.com>
     [not found]               ` <4EDD5F1B.5060205@nvidia.com>
     [not found]                 ` <CAPnjgZ2h7F228q=pXuf7M9vTASurY3R5an_QV-mrETLf8nzA1A@mail.gmail.com>
     [not found]                   ` <4EDE7E1C.2090203@nvidia.com>
     [not found]                     ` <CAPnjgZ1G+mv6uv8SrdMm7DoqFjeeyVHYv6nbQxn9qixfbQMGvA@mail.gmail.com>
     [not found]                       ` <CAPnjgZ1G+mv6uv8SrdMm7DoqFjeeyVHYv6nbQxn9qixfbQMGvA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2011-12-07 23:46                         ` [PATCH 10/14] tegra: usb: Add support for USB peripheral Stephen Warren
2011-12-08 21:24                           ` Simon Glass
     [not found]                             ` <CAPnjgZ0AuBNkYKN0JHQyc7DdzwUSZivR+Dv2BkiFsKQBNMeP8A-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2011-12-12 18:18                               ` Stephen Warren
2011-12-12 18:42                                 ` Simon Glass

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