Re: Need to use a I2C EEPROM on normal x86 architecture

[Christian Gmeiner <christian.gmeiner-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

2011/6/23 Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>:
> Hi Christian,
>
> On Tue, 21 Jun 2011 13:54:52 +0200, Christian Gmeiner wrote:
>> Hi community,
>>
>> I am working on an embedded x86 device, which has an at24 based
>> eeprom. I am using
>> the i2c_eg20t driver to access the i2c bus. To be able to access the
>> eeprom in a separated
>> driver I did this:
>>
>> /* technical description of our used EEPROM */
>> static struct at24_platform_data custom_i2c_eeprom_info = {
>>       .byte_len       = EEPROM_BYTE_LEN,
>>       .page_size      = 16,
>>       .flags          = 0,
>
> Note that you don't have to mention struct members with value 0 (or
> NULL), as this is the default.
>

Thanks for this hint.

>>       .setup          = content_read,
>>       .context        = NULL,
>> };
>>
>> /* EEPROM at24 */
>> static struct i2c_board_info __initdata i2c_info[] =  {
>>       {
>>               I2C_BOARD_INFO("24c04", 0x50),
>>               .platform_data  = &custom_i2c_eeprom_info,
>>       },
>> };
>>
>> In the init function of my custom driver I do this:
>>
>>       /* register known devices on i2c bus */
>>       status = i2c_register_board_info(0, i2c_info, ARRAY_SIZE(i2c_info))
>
> Out of curiosity, where did you put this code? Does x86 finally support
> per-machine initialization as e.g. arm does?
>

I have an other x86 based target machine, which runs a 2.6.36.4
kernel, where I created
a new driver under drivers/misc called custom_eeprom.c. The driver is
used to access
some special values stored in eeprom easily from userspace via /proc.

static int __init custom_eeprom_init(void)
{

    ...

	/* register known devices on i2c bus */
	status = i2c_register_board_info(0, i2c_info, ARRAY_SIZE(i2c_info));

	/* create procfs entries */

	...
	
	return ret;
}

It is AMD LX800 based an I use the scx200_acb i2c driver, modified to
use i2c_add_numbered_adapter().
I did a small test with 3.0-rc4 on the LX800 target, but it get an
oops.. so there seems to be some changes in the involved subsystems.

>>
>> Now I run in some troubles... see
>> http://www.spinics.net/lists/linux-i2c/msg02022.html
>
> I see that I already replied to this post...
>
>> What options do I have to get this running? I could use
>> i2c_add_numbered_adapter, but I don't
>> want to touch too much from mainline kernel sources.
>
> It seems difficult to use i2c_add_numbered_adapter() unconditionally, as
> i2c-eg20t is a PCI driver so you don't get to pass platform data to it.
> Furthermore, i2c_add_numbered_adapter() is only suitable if machine
> setup code could be run before any device driver is initialized;
> otherwise odds are that another driver will have picked the i2c bus
> number you wanted. I am unsure if this is possible at all on x86 at the
> moment.
>
> The way I would do it is from i2c-eg20t itself. Take a look at i2c-i801
> for an example: at the end of the probe function, there is
> hardware-specific code to instantiate a few I2C devices. If you have a
> way to uniquely, reliably detect that you are running on your specific
> target system, you can do the same.
>
> I don't think it is particularly nice, BTW, but this is the only way I
> found so far with what the i2c subsystem core offers. If anyone has
> suggestions how to improve this, please speak up.
>
> If you want to be able to use i2c_add_numbered_adapter() conditionally
> without the help of platform data, then you need a hint from i2c-core.
> Would the following patch help you? If it does, and others show
> interest, and there are no objections, this could go upstream in kernel
> 3.1.
>

I get an oops quite early in kernel bootup... I will try to catch it
and if you are
interested I will post it here.

> ---
>  drivers/i2c/busses/i2c-eg20t.c |    7 ++++++-
>  drivers/i2c/i2c-boardinfo.c    |   20 ++++++++++++++++++++
>  include/linux/i2c.h            |    5 +++++
>  3 files changed, 31 insertions(+), 1 deletion(-)
>
> --- linux-3.0-rc4.orig/drivers/i2c/i2c-boardinfo.c      2011-05-20 10:42:40.000000000 +0200
> +++ linux-3.0-rc4/drivers/i2c/i2c-boardinfo.c   2011-06-23 10:15:56.000000000 +0200
> @@ -90,3 +90,23 @@ i2c_register_board_info(int busnum,
>
>        return status;
>  }
> +
> +/**
> + * i2c_adapter_is_static - let drivers know if their bus is static
> + * @busnum: identifies the bus
> + *
> + * After calling this function, i2c bus drivers can decide whether
> + * to call i2c_add_adapter or i2c_add_numbered_adapter.
> + */
> +int
> +i2c_adapter_is_static(int busnum)
> +{
> +       int is_static;
> +
> +       down_write(&__i2c_board_lock);
> +       is_static = busnum < __i2c_first_dynamic_bus_num;
> +       up_write(&__i2c_board_lock);
> +
> +       return is_static;
> +}
> +EXPORT_SYMBOL_GPL(i2c_adapter_is_static);
> --- linux-3.0-rc4.orig/include/linux/i2c.h      2011-06-21 10:32:32.000000000 +0200
> +++ linux-3.0-rc4/include/linux/i2c.h   2011-06-23 09:58:21.000000000 +0200
> @@ -306,6 +306,7 @@ extern void i2c_unregister_device(struct
>  extern int
>  i2c_register_board_info(int busnum, struct i2c_board_info const *info,
>                        unsigned n);
> +extern int i2c_adapter_is_static(int busnum);
>  #else
>  static inline int
>  i2c_register_board_info(int busnum, struct i2c_board_info const *info,
> @@ -313,6 +314,10 @@ i2c_register_board_info(int busnum, stru
>  {
>        return 0;
>  }
> +static inline int i2c_adapter_is_static(int busnum)
> +{
> +       return 0;
> +}
>  #endif /* I2C_BOARDINFO */
>
>  /*
> --- linux-3.0-rc4.orig/drivers/i2c/busses/i2c-eg20t.c   2011-05-30 20:45:09.000000000 +0200
> +++ linux-3.0-rc4/drivers/i2c/busses/i2c-eg20t.c        2011-06-23 10:48:26.000000000 +0200
> @@ -787,7 +787,12 @@ static int __devinit pch_i2c_probe(struc
>
>                pch_adap->dev.parent = &pdev->dev;
>
> -               ret = i2c_add_adapter(pch_adap);
> +               if (i2c_adapter_is_static(i)) {
> +                       /* We assume that a single PCI device is present */
> +                       pch_adap->nr = i;
> +                       ret = i2c_add_numbered_adapter(pch_adap);
> +               } else
> +                       ret = i2c_add_adapter(pch_adap);
>                if (ret) {
>                        pch_pci_err(pdev, "i2c_add_adapter[ch:%d] FAILED\n", i);
>                        goto err_i2c_add_adapter;
>
>
>
> --
> Jean Delvare
>

--
Christian Gmeiner, MSc