linux-kernel - Re: SPI read problem

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Message-ID: <4DAEE410.8020000@cam.ac.uk>
Date:	Wed, 20 Apr 2011 14:48:00 +0100
From:	Jonathan Cameron <jic23@....ac.uk>
To:	"Murali K. Vemuri" <vemuri.muralikrishna@...il.com>
CC:	徐建辉 <xujianhui168@...il.com>,
	linux-kernel@...r.kernel.org,
	spi-devel-general@...ts.sourceforge.net,
	Grant Likely <grant.likely@...retlab.ca>
Subject: Re: SPI read problem

On 04/20/11 05:40, Murali K. Vemuri wrote:
> On Wed, Apr 20, 2011 at 12:19 PM, 徐建辉 <xujianhui168@...il.com> wrote:
>> you can use tasklet.
>>
>> 2011/4/19 Murali K. Vemuri <vemuri.muralikrishna@...il.com>
>>>
>>> Hello there,
>>> I have a device which is Written_to/Read_from using SPI Bus.
>>>
>>> I initialize the device like this:
>>>
>>> static int __init myDEV_init(void)
>>> {
>>>    return spi_register_driver(&myDEV_driver);
>>> }
>>> module_init(myDEV_init);
>>>
>>> My myDEV_probe() function looks like this:
>>>
>>> static int __devinit myDEV_probe(struct spi_device *spi)
>>> {
>>> .....
>>> .....
>>> /*when my CPU receives a particular IRQ, I have to do a spi_read() and
>>> do couple of spi_write(), I am using like this:*/
>>> err = request_threaded_irq (MY_DEV_IRQ, NULL, myDEV_irq_thread,
>>>            IRQF_TRIGGER_RISING, "MYDEV", NULL);
This should be fine.  The thread can sleep just fine. We do this
all over the place.  Could be something to do with the irq
handling on the device.
>>>
>>> return 0;
>>> }
>>>
>>> When the Interrupt is received by the CPU, myDEV_irq_thread is being
>>> called.
>>> However, in the ISR I have to do  spi_read(). This is always returning
>>> "Timed out".
That's very suspicious.  What spi controller are we dealing with here?
>>>
>>> To verify if the device is not at all working, along with registering
>>> for the IRQ, I also created a char device through I did a IOCTL.
>>> The IOCTL command in turn does spi_read(). In this case spi_read() is
>>> successful.
>>>
>>> Since it is necessary to do spi_read() in my ISR, I searched around
>>> and found some information that
>>> spi_read() is callable only from contexts that can sleep.
>>>
>>> How can I make my ISR sleep? or is there any other way of doing this?
>>>
>>> Any help is highly appreciated.
>>> Thanks & regards
>>> Murali
>>> --
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>>
>>
> 
> Hi there,
> 
> I tried using "tasklet", "workqueue" and semaphore ... all my attempts failed.
> if there is any other method I should try, please let me know.
Something nastier is happening here.  It's not a problem with what you've
presented in this email.  Perhaps a minimum example of the full code surrounding
the problem may help us diagnose it.  
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