linux-kernel - Re: [PATCH 1/3] staging:iio:magnetometer:ak8975 Don't use irq_to

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Date:	Thu, 01 Sep 2011 10:24:11 +0100
From:	Jonathan Cameron <jic23@....ac.uk>
To:	Jonathan Cameron <jic23@....ac.uk>
CC:	Stephen Warren <swarren@...dia.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Russell King <linux@....linux.org.uk>,
	Andrew Chew <achew@...dia.com>, Arnd Bergmann <arnd@...db.de>,
	linux-iio@...r.kernel.org, devel@...verdev.osuosl.org,
	linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH 1/3] staging:iio:magnetometer:ak8975 Don't use irq_to_gpio()

On 09/01/11 10:07, Jonathan Cameron wrote:
> On 08/31/11 20:40, Stephen Warren wrote:
>> Tegra doesn't have irq_to_gpio() any more, and ak8975 is included in
>> tegra_defconfig. This causes a build failure. Solve this with a heavy-handed
>> method for now.
>>
>> I suspect the long-term solution is to pass both the IRQ and GPIO IDs
>> to the driver; the GPIO ID coming from either platform data, or perhaps
>> enhancing struct i2c_client to add a gpio field alongside irq.
> Definitely on the platform data front. We need some means of doing this now
> hence my patch putting most trivial form of that in.

Actually taking the time to look at the code...

Can someone explain to me (I have a feeling I may just have forgotten this)
why we aren't using an interrupt here?  It looks like a bus transaction triggered
read.  So why not do a enable_irq followed by triggering the read and use a
waitqueue to wait for an interrupt handler to signal it is done?

Having found the datahsheeting lying around on the net I can't see why this
won't work and be somewhat cleaner than current polling approach.

Jonathan
>> Signed-off-by: Stephen Warren <swarren@...dia.com>
> Acked-by: Jonathan Cameron <jic23@....ac.uk>
>> ---
>> Russell, now that irq_to_gpio() is going away, can you comment on how
>> you'd like to fix drivers that do this kind of thing? Thanks.
>>
>>  drivers/staging/iio/magnetometer/ak8975.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/staging/iio/magnetometer/ak8975.c b/drivers/staging/iio/magnetometer/ak8975.c
>> index a17fa9f..bd40e32 100644
>> --- a/drivers/staging/iio/magnetometer/ak8975.c
>> +++ b/drivers/staging/iio/magnetometer/ak8975.c
>> @@ -477,7 +477,7 @@ static int ak8975_probe(struct i2c_client *client,
>>  	int err;
>>  
>>  	/* Grab and set up the supplied GPIO. */
>> -	eoc_gpio = irq_to_gpio(client->irq);
>> +	eoc_gpio = -1; /* FIXME: irq_to_gpio(client->irq) */
>>  
>>  	/* We may not have a GPIO based IRQ to scan, that is fine, we will
>>  	   poll if so */
> 
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