linux-kernel - Re: SPI read problem

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Date:	Thu, 21 Apr 2011 10:15:14 +0900
From:	"Murali K. Vemuri" <vemuri.muralikrishna@...il.com>
To:	Jonathan Cameron <jic23@....ac.uk>
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 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
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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.

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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