Date:	Fri, 06 May 2011 08:41:31 +0400
From:	Igor Plyatov <plyatov@...il.com>
To:	James Nuss <jamesnuss@...ometrics.ca>
CC:	Alexander Gordeev <lasaine@....cs.msu.su>,
	Rodolfo Giometti <rodolfo.giometti@...eenne.com>,
	linuxpps@...enneenne.com, linux-kernel@...r.kernel.org
Subject: Re: [LinuxPPS] [PATCH 2/2] pps: new client driver using IRQs

Hi James!

> Hi Igor,
>
> I agree, platform_data is a good candidate for this type of parameter.
> Where is the appropriate place to keep the header file containing the
> struct declaration(s)? e.g in your case "struct
> pps_client_gpio_platform_data" and "struct pps_client_gpio" Presumably
> it needs to be in a readily accessible header file so the board setup
> code can use it.

This header file must be "include/linux/pps-client-gpio.h".
Here is its content:

/*
  * pps-client-gpio.h -- PPS client for IRQ capable GPIO
  *
  *
  * Copyright (C) 2011 Igor Plyatov <plyatov@...il.com>
  *
  *   This program is free software; you can redistribute it and/or modify
  *   it under the terms of the GNU General Public License as published by
  *   the Free Software Foundation; either version 2 of the License, or
  *   (at your option) any later version.
  *
  *   This program is distributed in the hope that it will be useful,
  *   but WITHOUT ANY WARRANTY; without even the implied warranty of
  *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  *   GNU General Public License for more details.
  *
  *   You should have received a copy of the GNU General Public License
  *   along with this program; if not, write to the Free Software
  *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */

#ifndef _PPS_CLIENT_GPIO_H
#define _PPS_CLIENT_GPIO_H

struct pps_client_gpio {
     /* Configuration parameters */
     unsigned gpio;
     unsigned active_low;
     const char *desc;
     unsigned char decoder_type;
};

struct pps_client_gpio_platform_data {
     struct pps_client_gpio *pclient;
     int num_gpios;
};

#endif

> cheers,
> James
>
>> This way can lead to problems when developer tries to debug PPS subsystem
>> with some specific signal parameters.
>> In my opinion it much safer to explicitly declare ".active_low = 0" or
>> ".active_low = 1" in the platform initialization code.
>> See example:
>>
>> /*
>>   * pps client gpio
>>   */
>> static struct pps_client_gpio pps_client_gpios[] = {
>>     {
>>         .gpio            = GPI_PPS0_IN,
>>         .active_low        = 0, /* ASSERT is a _/ */
>>         .desc            = "pps0 source",
>>         .decoder_type        = PPS_DECODER_GEOSIG_T1PPS,
>>     },
>>     {
>>         .gpio            = GPI_PPS1_IN,
>>         .active_low        = 1, /* ASSERT is a \_ */
>>         .desc            = "pps1 source",
>>     }
>> };
>>
>> static struct pps_client_gpio_platform_data pps_client_gpios_data = {
>>     .pclient    = pps_client_gpios,
>>     .num_gpios    = ARRAY_SIZE(pps_client_gpios),
>> };
>>
>> static struct platform_device pps_client_gpio_device = {
>>     .name        = "pps-client-gpio",
>>     .id        = 0,
>>     .dev        = {
>>         .platform_data    =&pps_client_gpios_data,
>>     }
>> };
>>
>>
>>> If I was to implement the driver this way then you would have exactly
>>> 3 ways to register a device to use this driver:
>>>
>>> 1) Register an IRQ with only IORESOURCE_IRQ_HIGHEDGE set:
>>> This will generate an ASSERT event on rising edges (no CLEAR events)
>>>
>>> 2) Register an IRQ with only IORESOURCE_IRQ_LOWEDGE set:
>>> This will generate an ASSERT event on falling edges (no CLEAR events)
>>>
>>> 3) Register an IRQ with both IORESOURCE_IRQ_LOWEDGE and
>>> IORESOURCE_IRQ_HIGHEDGE set:
>>> This will generate ASSERT and CLEAR events with the driver dynamically
>>> determining which edge is the ASSERT based on the logic above.
>>>
>>> I hope this covers all the potential use cases.
>>>
>>> cheers,
>>> James
>>>
>>>
>>> On Fri, Apr 29, 2011 at 4:26 AM, Rodolfo Giometti<giometti@...eenne.com>
>>>   wrote:
>>>> On Fri, Apr 29, 2011 at 08:29:55AM +0400, Igor Plyatov wrote:
>>>>
>>>>>>> The latter will definitely mess things up, right?
>>>>>> I mean, one surely can register an IRQ resource with both flags set.
>>>>>> And
>>>>>> if the underlying hardware works as it is described (i.e. raises an irq
>>>>>> on both edges) then it will be a problem.
>>>>> Please don't try to abandon one of ASSERT or CLEAR events!
>>>>> It is very useful to register both of them, because in this case its
>>>>> possible to measure pulse width and decode PPS signals like DCF77.
>>>> At this point I suppose we should add both ASSERT and CLEAR events...
>>>>
>>>> Ciao,
>>>>
>>>> Rodolfo
>>>>
>>>> --
>>>>
>>>> GNU/Linux Solutions                  e-mail: giometti@...eenne.com
>>>> Linux Device Driver                          giometti@...ux.it
>>>> Embedded Systems                     phone:  +39 349 2432127
>>>> UNIX programming                     skype:  rodolfo.giometti
>>>> Freelance ICT Italia - Consulente ICT Italia - www.consulenti-ict.it
>>>> --
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>>>> Please read the FAQ at  http://www.tux.org/lkml/
>>>>
>> Best regards!
>>
>> --
>> Igor Plyatov
>>
>>

Best regards!
-- 

Igor Plyatov

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