Date:	Thu, 21 Apr 2011 11:33:04 +0900
From:	"Murali K. Vemuri" <vemuri.muralikrishna@...il.com>
To:	Pei Lin <telent997@...il.com>
Cc:	Jonathan Cameron <jic23@....ac.uk>,
	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

2011/4/21 Pei Lin <telent997@...il.com>:
> 2011/4/21 Murali K. Vemuri <vemuri.muralikrishna@...il.com>:
>> On Wed, Apr 20, 2011 at 10:48 PM, Jonathan Cameron <jic23@....ac.uk> wrote:
>>> 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
>>>>>> --
>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
>>>>>> the body of a message to majordomo@...r.kernel.org
>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>> 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.
>
I added "workqueue", and got the same result. Also, I used "tasklet"
and got the same result.
spi_async does not seem to be working for me, returning EINVAL (-22).
spi_sync() seem to be returning 0 (supposed to be success) but no data
coming out ... still investigating why ZEROS are returned instead of
valid data.

if you have any suggestions, please let me know.

Murali
>
>> 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
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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>> Please read the FAQ at  http://www.tux.org/lkml/
>>
>
>
>
> --
> Best Regards
> Lin
>
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