Re: SPI read problem

[Pei Lin]

2011/4/21 Murali K. Vemuri <vemuri.muralikrishna@xxxxxxxxx>:
> On Wed, Apr 20, 2011 at 10:48 PM, Jonathan Cameron <jic23@xxxxxxxxx> wrote:
>> On 04/20/11 05:40, Murali K. Vemuri wrote:
>>> On Wed, Apr 20, 2011 at 12:19 PM, 徐建辉 <xujianhui168@xxxxxxxxx> wrote:
>>>> you can use tasklet.
>>>>
>>>> 2011/4/19 Murali K. Vemuri <vemuri.muralikrishna@xxxxxxxxx>
>>>>>
>>>>> 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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>>>>> Please read the FAQ at  http://www.tux.org/lkml/
>>>>
>>>>
>>>
>>> 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.
>>
>
> Thanks a lot for the inputs. this is the read function I have:
> (What  I am trying to do is read register E6 of my device, the
> register width is 16 bits.).
>
> static struct spi_device * my_SPI_DEV; (this is populated in the probe function)
>
> static int myDEV_read(u8 * buf, u16 len)
> {
>    int err;
>    err = spi_read(my_SPI_DEV, buf, len);
>    return err;
> }
> static int read_e6()
> {
>    u8 buf[3];
>    int err;
>    buf[0] = 0xe6;
>    buf[1] = 0x00;
>    buf[2] = 0x00;
>    err = myDEV_read(buf, 3);
>    printk(KERN_ERR "myDEV read returned: %d\n",err);
>    return err;
> }
>
> Now, this function read_e6() is called from the ISR I mentioned above.
>


spi_read will call spi_sync and this call may only be used from a
context that may sleep.  The sleep
 is non-interruptible, and has no timeout. should use in
non-interruptable context.
you should put the spi_read on context which can sleep, as bottom half
"work queue"
Or use spi_async interface.


> 90% of time, the read returns "-5" (I/O Error) and about 10% time it
> gets "0".  However I added a little hexdump to check the content in
> case the return value is "0". The register content is always "0".
>
> Please let me know if I am doing any mistake.
> Thanks & regards
> Murali
> --
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>



-- 
Best Regards
Lin
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